Mobile cellphone charger

While travelling charging of mobile battery is great problem because power supply source is not generally accessible. Here is a simple project using very common electronics components for charging mobile battery using AA cells.<br /> <h3 style="text-align: center;"> Circuit descriptions of mobile cellphone charger</h3> The main part of the circuit mobile cellphone charger is timer IC NE555, used to charge and monitor the voltage level. IC₁ get control voltage to pin 5 by zener diode ZD₁­. Threshold pin 6 and trigger pin 2 is supplied with a voltage set by VR₁ and VR₂ respectively. The trigger pin 2 of IC₁ is below 1/3V_CC when discharge battery is connected to the circuit as a result flip-flop of IC₁ is switched on to take output pin 3 high. The process is reversed when battery is fully charged of charged battery is connected. Here transistor T₁ used to enhance the charging current from output pin 3 of IC₁. Adjust potentiometer VR₁ and VR₂ as per require.<br /> <br /> <h4 style="text-align: center;"> LED status for different charging conditions</h4> <table border="1" cellpadding="0" cellspacing="0"> <tbody> <tr> <td valign="top" width="213">Load across the output</td> <td valign="top" width="213">Output frequency (at pin 3)</td> <td valign="top" width="213">LED₁</td> </tr> <tr> <td valign="top" width="213">No battery connected</td> <td valign="top" width="213">765 kHz</td> <td valign="top" width="213">On</td> </tr> <tr> <td valign="top" width="213">Charging battery</td> <td valign="top" width="213">4.5 Hz</td> <td valign="top" width="213">Blink</td> </tr> <tr> <td valign="top" width="213">Fully charged battery</td> <td valign="top" width="213">0</td> <td valign="top" width="213">Off</td> </tr> </tbody> </table> <h3 style="text-align: center;"> <div class="separator" style="clear: both; text-align: center;"> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiwh3UDU3rSzeJ_IP779glXl6Y6IoMK3GAZn41V0hFfr7A6S4iSFXrib1gf89q7TmpHVYdXJMJmCVyxiX8Oe05nVo_4sgtf3-xjCqRA06ypYZU8XsTs5WjVB6niG0ODM1BRHM0jfokHaQI/s1600/mobile-battery-charger.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="231" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiwh3UDU3rSzeJ_IP779glXl6Y6IoMK3GAZn41V0hFfr7A6S4iSFXrib1gf89q7TmpHVYdXJMJmCVyxiX8Oe05nVo_4sgtf3-xjCqRA06ypYZU8XsTs5WjVB6niG0ODM1BRHM0jfokHaQI/s1600/mobile-battery-charger.jpg" width="400" /></a></div> </h3> <h3 style="text-align: center;">  PARTS LIST</h3> <div align="center" style="text-align: center;"> <b>Resistors (all ¼-watt, ± 5% Carbon)</b></div> <div style="text-align: center;"> R₁ = 390 Ω</div> <div style="text-align: center;"> R₂ = 680 Ω</div> <div style="text-align: center;"> R₃ = 39 Ω/1W</div> <div style="text-align: center;"> R₄ = 27 KΩ</div> <div style="text-align: center;"> R₅ = 47 KΩ</div> <div style="text-align: center;"> R₆ = 3.3 KΩ</div> <div style="text-align: center;"> R₇ = 100 Ω/1W</div> <div style="text-align: center;"> VR₁, VR₂ = 20 KΩ</div> <h4 style="text-align: center;"> Capacitors</h4> <div style="text-align: center;"> C₁ = 0.001 µF (ceramic disc)</div> <ins style="border: none; display: inline-table; height: 90px; margin: 0; padding: 0; position: relative; visibility: visible; width: 728px;"><ins id="aswift_1_anchor" style="border: none; display: block; height: 90px; margin: 0; padding: 0; position: relative; visibility: visible; width: 728px;"></ins></ins><div style="text-align: center;"> C₂ = 0.01 µF (ceramic disc)</div> <div style="text-align: center;"> C₃ = 4.7 µF/25V (Electrolytic )</div> <h4 style="text-align: center;"> Semiconductors</h4> <div style="text-align: center;"> IC₁ = NE555 timer IC</div> <div style="text-align: center;"> T₁ = SL100</div> <div style="text-align: center;"> ZD₁ = 5.6 V/1W</div> <div style="text-align: center;"> LED₁</div> <ins style="border: none; display: inline-table; height: 90px; margin: 0; padding: 0; position: relative; visibility: visible; width: 728px;"><ins id="aswift_2_anchor" style="border: none; display: block; height: 90px; margin: 0; padding: 0; position: relative; visibility: visible; width: 728px;"></ins></ins><h4 style="text-align: center;"> Miscellaneous</h4> <div style="text-align: center;"> SW₁ = On/off switch</div> <div style="text-align: center;"> 1.5V*8 AA cells</div> <div style="text-align: center;"> Mobile connector</div>

Mobile cellphone charger

While travelling charging of mobile battery is great problem because power supply source is not generally accessible. Here is a simple pro...

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Clap operated Remote Control for Fans

Here is the circuit of clap-operated remote control fans is used to control not only switching properties but also control speed of fan. The main advantage of clap operated remote control for fan is, it can control up to ten-step speeds of fan where normally a fan has three to five step speeds.<br /> <h3 style="text-align: center;"> Circuit description clap operated remote control for fan</h3> This entire circuit clap operated remote control for fan is divided into four major section i.e. sound-operated trigger pulse generator, clock pulse generator, clock pulse counter and load operator.<br /> <b>Sound-operated trigger pulse</b>: – The heart of this section is transistor T₁ BC148, configured as class-C amplifier mode. The MIC₁ is used to change voice signal into its corresponding electrical signal and is given to base of transistor T₁ in order to amplify and increase its intensity.<br /> <b>Clock pulse generator</b>:- This section is build around timer IC NE555 and configured as monostable multivibrator. The trigger pulse generated by transistor T₁ is given to pin 2 of IC₁ and time period (T) for output high is calculated by formula.<br /> <div style="text-align: center;"> <b>T = 1.1RC</b></div> <b>Clock Pulse counter</b>:- This section is build around decade counter CD4017BC which counts the clock pulse generated by timer IC (IC₁). The output from IC₁ is given to pin 14 of IC₂. IC₂ has ten outputs, viz, o, 1, 2, 3, 4…..9. Here we use only three outputs i.e. output 1, 2 and 3 from pin 2, 4, and 7 respectively. Output 4 from pin 10 is directly connected to reset pin 15.<br /> <b>Load operator</b>:- This section is build around three transistor as relay driver to operate three separate relay. Output from each pin of IC₂ is given to base of each transistor through 100Ω and LED as shown in circuit diagram. Output is taken from collector of transistor and is connected to relay. The three LEDs used to indicate gear or speed i.e. LED₁, LED₂ & LED₃ indicates gear 1, gear 2 & gear 3 respectively.<br /> <br /> <div class="separator" style="clear: both; text-align: center;"> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgd_QPLgqEuto1ltkPo5vPVMUMbt7J8CVbqMwRmrsnUQHvWr41jIyf1zJ62Y_ya1LDDLrtJgDhjuUi1cBB6-g0nRM72S8EXXeVNgkT5qDyHlW5lPbIz-GLSTC9blDZNoPwTP-pOzXXQ5O8/s1600/Circuit-diagram-of-clap-operated-remote-fan-switch2.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="440" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgd_QPLgqEuto1ltkPo5vPVMUMbt7J8CVbqMwRmrsnUQHvWr41jIyf1zJ62Y_ya1LDDLrtJgDhjuUi1cBB6-g0nRM72S8EXXeVNgkT5qDyHlW5lPbIz-GLSTC9blDZNoPwTP-pOzXXQ5O8/s1600/Circuit-diagram-of-clap-operated-remote-fan-switch2.jpg" width="640" /></a></div> <br /> <br /> <b>NOTE:-</b><b>This circuit used to operate in 1^st speed similarly, 2^nd clap for 2^nd speed, 3^rd clap for 3^rd speed and 4^th clap to switch off the fan.</b><br /> <h3 style="text-align: center;"> PARTS LIST</h3> <div style="text-align: center;"> <b>Resistors (all ¼-watt, ± 5% Carbon)</b></div> <div style="text-align: center;"> R₁ = 10 KΩ</div> <div style="text-align: center;"> R₂ = 1.2 MΩ</div> <div style="text-align: center;"> R₃ = 2.2 KΩ</div> <div style="text-align: center;"> R₄ = 150 KΩ</div> <div style="text-align: center;"> R₅ = 220 KΩ</div> <div style="text-align: center;"> R₆ = 10 KΩ</div> <div style="text-align: center;"> R₇, R₈, R₉ = 100 Ω</div> <h4 style="text-align: center;"> Capacitors</h4> <div style="text-align: center;"> C₁, C₂ = 0.1 µF/16V</div> <ins style="border: none; display: inline-table; height: 90px; margin: 0; padding: 0; position: relative; visibility: visible; width: 728px;"><ins id="aswift_1_anchor" style="border: none; display: block; height: 90px; margin: 0; padding: 0; position: relative; visibility: visible; width: 728px;"></ins></ins><div style="text-align: center;"> C₃ = 4.7 µF/16V</div> <div style="text-align: center;"> C₄ = 0.01 µF (ceramic disc)</div> <div style="text-align: center;"> C₅ = 1000 µF/12V</div> <h4 style="text-align: center;"> Semiconductors</h4> <div style="text-align: center;"> IC₁ = NE555 (Timer IC)</div> <div style="text-align: center;"> IC₂ = CD4017BE (decade counter)</div> <div style="text-align: center;"> T₁ = BC148</div> <div style="text-align: center;"> T₂, T₃, T₄ = BEL187</div> <div style="text-align: center;"> D₁, D₂ = 1N4001 silicon diode</div> <h4 style="text-align: center;"> Miscellaneous</h4> <div style="text-align: center;"> MIC₁ = Condenser microphone 34LOD</div> <div style="text-align: center;"> LED₁ = Green</div> <div style="text-align: center;"> LED₂ = yellow</div> <div style="text-align: center;"> LED₃ = RED</div>

Clap operated Remote Control for Fans

Here is the circuit of clap-operated remote control fans is used to control not only switching properties but also control speed of fan. Th...

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555 Duty Cycle Control

Here is a simple oscillator circuit that varies the duty cycle over a wide range without affecting the frequency. It is a variation of the simple 555 astable oscillator. Initially, I told a reader that there was no standard 555 circuit that could do this, but then the grey matter started working. The use of an air-variable capacitor for frequency control is a mind-blower—nothing short of a time warp!<br /> <span id="more-6950"></span><br /> <ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_0_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins><br /> <b>555 Duty Cycle Control Schematic</b> <br /> <a href="http://electroschematics.com/wp-content/uploads/2012/10/555-Duty-Cycle-Control-Schematic.jpg" target="_blank"><img alt="555 Duty Cycle Control Schematic" class="alignnone size-large wp-image-6951" height="380" src="http://electroschematics.com/wp-content/uploads/2012/10/555-Duty-Cycle-Control-Schematic-550x380.jpg" title="" width="550" /></a><br /> <b>Overview</b><br /> When potentiometer R1 is centered, operation is obvious and the duty cycle is 50%. However, as R1 is rotated in either direction the charge time and discharge times vary accordingly. The two sides of R1 have independent steering diodes (D1 & D2). C1 & C2 make up the timing capacitor. Pins 2 & 6 of the 555 are the upper and lower thresholds of the input comparators. The charge /discharge voltage is taken from pin 3 because it has rail-to-rail voltage swing, and the open collector output (pin 7) cannot do this. The rectangular waveform output is taken from pin 7 instead. R3 is the pull-up resistor.<br /> If constant frequency is desired, C1 could be padded for the correct frequency. However, most experimenters also want variable frequency. Since R1 cannot be varied in total resistance, it cannot vary the frequency. R2 could vary the frequency, but would also affect the duty cycle ratio limits as well. The only practical means of obtaining variable frequency is to vary C1.<br /> <b>Mathematical proof</b><br /> Q = I * T – where Q is the charge, I is charge current and T is charge time<br /> Q = C * V – where Q is charge, C is capacitance, and V is voltage across the capacitor<br /> ∴ I * T = C * V <br /> E = I * R – where E is voltage I is current and R is resistance<br /> ∴ I * T = C * I * R – because E is simply another expression for V<br /> T = C * R – dividing by I—we have now proved that charge time is directly proportional to R<br /> So we have a charge resistance and a discharge resistance, the sum of which is constant and equal to the R1 potentiometer total resistance (1 to 3). Therefore, the sum of the charge and discharge times is also constant. Since F = 1/T, the frequency is also be constant.<br /> In other words, the two resistances are complementary and the two time periods are likewise complementary.<br /> <b>The Air Variable Capacitor</b><br /> The old-fashioned air variable capacitor is old and klunky. While DigiKey offers no such product, these devices remain available on eBay as used or old stock. Every serious experimenter should have one of these. The one I would buy is a 3-gang 440pf. Wired in parallel the total capacitance is 1320pf. Physical size limitations prevent higher capacitances.<br /> Actually, it is fun to play with air variable capacitors.<br /> <b>High impedances</b><br /> To obtain a reasonably low frequency, R1 had to be selected to have as high a resistance as possible. 2M is the highest value pot I had on hand. A 5M would also be a good selection. To function under such high impedance conditions, I selected the TLC555 CMOS 555. A further advantage of this device is that it has rail-to-rail output voltage—something that the bipolar 555 cannot do.<br /> <b>Limits of accuracy</b><br /> The accuracy tends to degrade when the slew rate at C1 exceeds about 0.25V/uS. When this happens, the propagation delay of the comparators becomes significant and the frequency drops somewhat. This causes the peaks of the saw-tooth waveform to “skid” past the thresholds before the output switches polarity. This forces the maximum frequency to be lower than about 50kHZ for 50% duty cycle, or lower than 2kHZ with 98% duty cycle. To maintain 1 or 2% frequency accuracy the duty cycle range must drop as frequency increases.<br /> <b>Bench test set-up</b><br /> <br /> <div class="ngg-galleryoverview" id="ngg-gallery-2-6950"> <div class="ngg-gallery-thumbnail-box" id="ngg-image-7"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_2" href="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control/bench-setup.jpg" title=" "> <img alt="bench setup" src="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control/thumbs/thumbs_bench-setup.jpg" title="bench setup" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-8"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_2" href="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control/protoboard-closeup.jpg" title=" "> <img alt="protoboard closeup" height="75" src="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control/thumbs/thumbs_protoboard-closeup.jpg" title="protoboard closeup" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-9"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_2" href="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control/protoboard.jpg" title=" "> <img alt="protoboard" height="75" src="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control/thumbs/thumbs_protoboard.jpg" title="protoboard" width="100" /> </a> </div> </div> </div> <b>Oscillographs</b><br /> <br /> <div class="ngg-galleryoverview" id="ngg-gallery-3-6950"> <div class="ngg-gallery-thumbnail-box" id="ngg-image-10"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_3" href="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control-oscillographs/5-duty-cycle.jpg" title=" "> <img alt="5% duty cycle" height="75" src="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control-oscillographs/thumbs/thumbs_5-duty-cycle.jpg" title="5% duty cycle" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-11"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_3" href="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control-oscillographs/50-duty-cycle.jpg" title=" "> <img alt="50% duty cycle" height="75" src="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control-oscillographs/thumbs/thumbs_50-duty-cycle.jpg" title="50% duty cycle" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-12"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_3" href="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control-oscillographs/95-duty-cycle.jpg" title=" "> <img alt="95% duty cycle" height="75" src="http://electroschematics.com/wp-content/gallery/555-duty-cycle-control-oscillographs/thumbs/thumbs_95-duty-cycle.jpg" title="95% duty cycle" width="100" /> </a> </div> </div> </div> <b>For the future</b><br /> Novel VCO circuit<br /> <b>Glossary of undocumented words</b> (for our ESL friends)<br /> Klunky – adjective – variation of clunky – big, cumbersome, ugly, outmoded…<br /> <div class="info"> <a href="http://electroschematics.com/650/lm555-datasheet/" target="_blank">555 datasheet</a></div>

555 Duty Cycle Control

Here is a simple oscillator circuit that varies the duty cycle over a wide range without affecting the frequency. It is a variation of the...

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555 (TLC555) Relay Driver Circuit

Many integrated circuits have undocumented features or abilities. This is one of them. The TLC555 output (pin 3) can sink a 100mA load to 1.28V. The open drain transistor reset (pin 7) can sink 100mA to 1V. Tying both lines together is permissible because they are logically the same polarity and this potentially doubles the sink current ability to 200mA. This is ideal for driving my 133mA relay coil.<br /> The input also has the undocumented, but better known, feature of a Schmitt trigger that provides positive switching.<br /> <span id="more-7103"></span><br /> <ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_0_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins><br /> <span style="font-family: "Trebuchet MS",sans-serif; font-size: large;">555 Relay Driver Schematic</span><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/11/TLC555-Relay-Driver-Schematic.jpg" target="_blank"><img alt="TLC555 Relay Driver Schematic" class="alignnone size-large wp-image-7106" height="392" src="http://electroschematics.com/wp-content/uploads/2012/11/TLC555-Relay-Driver-Schematic-550x392.jpg" title="" width="550" /></a><br /> <b>Protoboard setup </b> <br /> <a href="http://electroschematics.com/wp-content/uploads/2012/11/Protoboard.jpg" target="_blank"><img alt="" class="alignnone size-large wp-image-7105" height="412" src="http://electroschematics.com/wp-content/uploads/2012/11/Protoboard-550x412.jpg" title="" width="550" /></a><br /> <b>Output current rating (pin 3): TLC555 vs. NE555</b><br /> <table style="width: 500px;"> <tbody> <tr> <th>(Vcc = 15V)</th> <th>TLC555</th> <th>NE555</th> </tr> <tr> <td>Source current</td> <td>10mA</td> <td>200mA</td> </tr> <tr> <td>Source mode saturation voltage</td> <td>Vcc-0.8V</td> <td>Vcc-2.5V</td> </tr> <tr> <td>Sink current</td> <td>100mA</td> <td>200mA</td> </tr> <tr> <td>Sink mode saturation voltage</td> <td>1.28V</td> <td>2.5V</td> </tr> </tbody></table> While it can be seen that the NE555 has the higher current rating, its saturation voltage is grossly inferior and this is a detriment in driving loads without excessive voltage drop. Also it can be seen that the TLC555 is much like TTL in that its sourcing ability is far less than its sinking ability. However for driving a relay, we are interested only in current sinking properties.<br /> <b>Relay out of my junk box</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/11/12V-Contactor.jpg" target="_blank"><img alt="12V Contactor" class="alignnone size-large wp-image-7104" height="412" src="http://electroschematics.com/wp-content/uploads/2012/11/12V-Contactor-550x412.jpg" title="" width="550" /></a><br /> This is a 40A automotive relay (contactor) that I selected for this application. Since its coil current exceeds the TLC555 output sink current rating, it is a good candidate. Manufacturer or part number is unknown.<br /> <ul> <li>Contact rating: 40A (from memory)</li> <li>Coil resistance: 90Ω cold</li> <li>Coil current: 133mA</li> <li>Coil power: 1.6W</li> <li>Coil voltage: 12V</li> <li>Pickup voltage: 4.8V cold</li> <li>Dropout voltage: 2.1V cold</li> <li>Operate time: 4.5mS</li> </ul> What is the difference between a relay and a contactor? There is no clear difference other than perhaps current rating and/or application—to me, relays are anything from signal devices to approx 20A. Anything rated at 40A or larger, or is used in power applications is a contactor.<br /> <b>Schmitt trigger input</b><br /> The trigger input (pin 2) and the threshold input (pin 6) pins are tied together—this is commonly done. With a 12V supply, the upper threshold is 8V and the lower is 4V. The two voltage levels, being far apart, make a great Schmitt trigger. This may be driven directly by 4000series CMOS logic that is also powered via 12V.<br /> To make it compatible with TTL logic levels, simply add the two resistors that are shown in the schematic. This loads down the internal divider to a lower voltage. The calculated levels are approx. 1.4 and 2.8V respectively.<br /> <b>Testing the performance</b><br /> <ul> <li>Output saturation voltage: <ul> <li>0.617V @ 133mA</li> <li>1.043V @ 200mA</li> </ul> </li> <li>TTL high level threshold: 3.0V</li> <li>TTL low level threshold: 1.6V</li> </ul> <b>How about the bipolar 555 and other variants?</b><br /> The standard 555 saturates poorly (2.5V) at 200mA and its reset line (pin 7) is not specified above 15mA, so it is not recommended. The intersil 7555 is a very low power device, so that is not recommended either.<br /> <b>For the future</b><br /> <ul> <li>Assorted relay driver circuits</li> <li>555 Voltage doubler relay driver circuit</li> <li>Relay economy circuits</li> </ul> <div class="info"> <a href="http://electroschematics.com/650/lm555-datasheet/" target="_blank" title="tlc555 datasheet">555 datasheet</a></div>

555 (TLC555) Relay Driver Circuit

Many integrated circuits have undocumented features or abilities. This is one of them. The TLC555 output (pin 3) can sink a 100mA load to...

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Inverted 555 Timer Circuit

Whenever I use the 555 timer, it seems that the output polarity is invariably incorrect, and the way the 555 functions, it normally cannot generate a duty cycle of less than 50% — 90% yes, 10% NO! This inverted 555 circuit generates duty cycles of less than 50%. Everything works the same except for the polarity. Why not simply invert the output with a transistor? Will not that do the same? Legitimate question… Actually NO, because a transistor that inverts the output cannot provide the desirable totem pole source/sink output function of pin 3. And there is another reason that we will get in the future—this is a 555VCO circuit that requires the inverted timer.<br /> <span id="more-7114"></span><br /> <ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_0_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins><br /> <h2> Inverted 555 Timer Schematic</h2> <a href="http://electroschematics.com/wp-content/uploads/2012/11/Inverted-555-Timer-Schematic.jpg" target="_blank"><img alt="Inverted 555 Timer Schematic" class="alignnone size-large wp-image-7117" height="550" src="http://electroschematics.com/wp-content/uploads/2012/11/Inverted-555-Timer-Schematic-540x550.jpg" title="" width="540" /></a><br /> The schematic shows (3) circuits, because one circuit does not work well over the entire Vcc range.<br /> The first simply uses a “normal” 2N3904 garden variety transistor, and this works well when Vcc < 9V. When Vcc > 9V, the base to emitter junction starts to zener and disrupts operation. Transistor base to emitter junction zeners a little above -6V.<br /> The second circuit adds D1 to the emitter of Q1 in order to increase VEBO. With this mod, Vcc may be increased to the 18V limit. However, D1 may be eliminated if we use the special 2SC2878 switching transistor that has a VBEO rating of -25V. These devices are no longer in production, but are available on eBay—every serious experimenter should have a few in his component collection. The types now in production use the tiny SO-23 SMD package.<br /> The third circuit uses a J112 N-Channel JFET for Q1. The JFET is a curious device that works well for the application provided we allow for the VGS(OFF) parameter. VGS must be less than Vcc /3. (e.g. if Vcc = 9V, VGS(OFF) must be less than 9V /3 or 3V for proper operation). Since the VGS(OFF) parameter is sloppy (-1 to -5V), the device must be selected—to the left is a simple test circuit—actually, most devices will work OK. The J112 should also be in every serious experimenter’s component collection.<br /> <b>Inverted 555 Oscillograph</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/11/Oscillograph-Inverted-555.jpg" target="_blank"><img alt="Oscillograph Inverted 555" class="alignnone size-full wp-image-7118" height="408" src="http://electroschematics.com/wp-content/uploads/2012/11/Oscillograph-Inverted-555.jpg" title="" width="498" /></a><br /> <b>How it works</b><br /> You will note that C1 is tied to Vcc rather than common and that R1 & R2 charge it in the negative direction. By connecting C1 to Vcc, the relatively high discharge current does not run through the power source. The reset transistor (Q1) discharges the capacitor in the positive direction. R1 & R2 are determined in the same fashion as the normal 555 timer. R3 is a pull-up resistor for the open collector output (pin 7) so it can drive the emitter follower (or source follower) reset transistor.<br /> R1 scales the output frequency—here it is about 1.25kHZ and it can be rescaled to whatever you need.<br /> R2 controls the reset pulse width for low duty cycle (short output pulse) output—the larger it gets, the more it affects output frequency.<br /> Pin 5 does not need a bypass capacitor unless you desire high stability—generally I omit this capacitor.<br /> <b>Protoboard setup</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/11/Protoboard-Setup.jpg" target="_blank"><img alt="Inverted 555 Protoboard Setup" class="alignnone size-large wp-image-7119" height="412" src="http://electroschematics.com/wp-content/uploads/2012/11/Protoboard-Setup-550x412.jpg" title="" width="550" /></a><br /> <b>For the future</b><br /> 555 VCO circuit<br /> <b>Preferred components for the serious experimenter</b><br /> 2SC2878 – <a href="http://electroschematics.com/wp-content/uploads/2012/11/2sc2878-datasheet.pdf" target="_blank" title="2sc2878 datasheet">datasheet</a><br /> J112 N-Channel JFET transistor – <a href="http://electroschematics.com/wp-content/uploads/2012/11/J111-Datasheet.pdf" target="_blank" title="J111 Datasheet">datasheet</a><br /> NE555 timer IC – <a href="http://electroschematics.com/650/lm555-datasheet/" target="_blank" title="555 datasheet">datasheet</a><br /> 2N4148 signal diode, 100V, 150mA (garden variety diode) (same as 1N916) (1N914 is rated at 75V)<br /> <b>Glossary of undocumented words and idioms</b> (for our ESL friends)<br /> garden variety –idiom—literally something that grows in your garden—commonly available component<br /> <div class="info"> <a href="http://electroschematics.com/650/lm555-datasheet/" target="_blank">555 datasheet</a></div>

Inverted 555 Timer Circuit

Whenever I use the 555 timer, it seems that the output polarity is invariably incorrect, and the way the 555 functions, it normally cannot ...

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Wide Frequency Range 555 VCO

The 555 frequency can be varied via adjusting the voltage at pin 5. However, the range and linearity of frequency adjustment is very limited. This is a way to greatly improve performance using the inverted 555 timer circuit that was previously posted.<br /> <span id="more-7170"></span><br /> <ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_0_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins><br /> <span style="font-size: large;"><b>555 VCO Schematic</b></span><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/11/Wide-Range-555-VCO-Circuit.jpg" target="_blank"><img alt="Wide Range 555 VCO Circuit Schematic" class="alignnone size-large wp-image-7178" height="270" src="http://electroschematics.com/wp-content/uploads/2012/11/Wide-Range-555-VCO-Circuit-550x270.jpg" title="" width="550" /></a><br /> <b>Current source</b><br /> Q2 is connected in the common base configuration. In this mode of operation, the collector current is a function of emitter current regardless of the collector voltage. In this way, it can perform a linear charge function upon C1. The emitter must be driven from a negative supply voltage. Frequency is scaled to 10V = 10kHZ via R5. Frequency range in this set-up is 180 to 10kHZ.<br /> <b>Bias transistor</b><br /> Q3 is wired as a self-biasing transistor by connecting the base to the collector and feeding it a bias current via R4. Voltage drop is 0.6V. Originally, I had a 1N4148 diode and its voltage drop was 0.45V that added too much offset to the emitter of Q1. Ideally, the voltage drop across Q3 should equal Vbe of Q2. This is a compromise because they are matched only under the condition of Ie = (9V – 0.6V) /R4 = 84uA. The emitter current varies from about 3 to 303uA. <br /> Lowest low end offset would occur with both transistors matched and R4 increased to 3M—in that case, the hFE @ 3uA must >100—this looks practical, but would require a different transistor selection—I did not experiment with this option.<br /> <b>Reset transistor</b><br /> Q1 is a 2N4401. It varies from the 2N3904 in that its current gain (hFE) is optimized at a higher current. The reset current must be high due to its low duty cycle.<br /> <b>Oscillographs</b><br /> <div class="ngg-galleryoverview" id="ngg-gallery-5-7170"> <div class="ngg-gallery-thumbnail-box" id="ngg-image-31"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_5" href="http://electroschematics.com/wp-content/gallery/wide-frequency-range-555-vco-oscillographs/waveform-1.jpg" title=" "> <img alt="waveform-1" height="75" src="http://electroschematics.com/wp-content/gallery/wide-frequency-range-555-vco-oscillographs/thumbs/thumbs_waveform-1.jpg" title="waveform-1" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-32"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_5" href="http://electroschematics.com/wp-content/gallery/wide-frequency-range-555-vco-oscillographs/waveform-2.jpg" title=" "> <img alt="waveform-2" height="75" src="http://electroschematics.com/wp-content/gallery/wide-frequency-range-555-vco-oscillographs/thumbs/thumbs_waveform-2.jpg" title="waveform-2" width="100" /> </a> </div> </div> </div> <b>Linearity</b><br /> <div class="ngg-galleryoverview" id="ngg-gallery-6-7170"> <div class="ngg-gallery-thumbnail-box" id="ngg-image-33"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_6" href="http://electroschematics.com/wp-content/gallery/wide-frequency-range-555-vco-linearity/linear-graph.jpg" title=" "> <img alt="linear-graph" height="75" src="http://electroschematics.com/wp-content/gallery/wide-frequency-range-555-vco-linearity/thumbs/thumbs_linear-graph.jpg" title="linear-graph" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-34"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_6" href="http://electroschematics.com/wp-content/gallery/wide-frequency-range-555-vco-linearity/log-graph.jpg" title=" "> <img alt="log-graph" height="75" src="http://electroschematics.com/wp-content/gallery/wide-frequency-range-555-vco-linearity/thumbs/thumbs_log-graph.jpg" title="log-graph" width="100" /> </a> </div> </div> </div> Linearity is shown over two orders of magnitude. While not perfect, it shows how the circuit performs. The error on the low end is caused by input offset voltage that is not perfectly nulled via the voltage drop of Q3. On the high end, non-linearity is caused by the finite reset time of the 555 that runs about 6% @ 10kHZ.<br /> <b>Spread sheet data </b> <br /> <div class="download-archive"> <a href="http://electroschematics.com/wp-content/uploads/2012/11/Wide-Range-555-VCO.rar" target="_blank" title="vco transfer function">link to wide range 555 VCO.xls</a></div> <b>Protoboard setup</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/11/Protoboard-setup.jpg" target="_blank"><img alt="" class="alignnone size-large wp-image-7175" height="412" src="http://electroschematics.com/wp-content/uploads/2012/11/Protoboard-setup-550x412.jpg" title="" width="550" /></a><br /> There is some extra stuff here to generate a -10V reference from a single 19V supply.<br /> <b>Disadvantages</b><br /> Frequency is a function of Vcc—requires stable supply<br /> High component count<br /> Requires negative reference voltage—no issue if already using split supply<br /> <b>Conclusion</b><br /> I do not generally recommend this circuit, but believe that it would make a great lab experiment for those who really want to learn more about VCO’s and the versatile 555.<br /> <b>For the future</b><br /> XR4151 VCO circuit<br /> Charge pump VCO circuit<br /> <b>Preferred components for the serious experimenter</b><br /> <div class="sectiune"> <a href="http://electroschematics.com/wp-content/uploads/2012/11/2N4401.jpg" target="_blank"><img alt="2N4401" class="alignleft size-thumbnail wp-image-7172" height="100" src="http://electroschematics.com/wp-content/uploads/2012/11/2N4401-100x100.jpg" title="" width="100" /></a><br /> 2N4401, 600mA, 60V, hFE = 100 @ 150mA<br /> Digikey 2N4401-ND<br /> $0.20 each<br /> EBC pinout <br /> <div class="download-pdf"> <a href="http://electroschematics.com/wp-content/uploads/2012/11/2N4401.pdf" target="_blank">2N4401 datasheet</a></div> </div> <div class="sectiune"> <a href="http://electroschematics.com/wp-content/uploads/2012/11/2N3904.jpg" target="_blank"><img alt="2N3904" class="alignleft size-thumbnail wp-image-7171" height="100" src="http://electroschematics.com/wp-content/uploads/2012/11/2N3904-100x100.jpg" title="" width="100" /></a><br /> 2N3904, 200mA, 60V, hFE = 100 @ 10mA,<br /> Digikey 2N3904FS-ND<br /> $0.18 each<br /> EBC pinout <br /> <div class="download-pdf"> <a href="http://electroschematics.com/wp-content/uploads/2012/11/MMBT3904.pdf" target="_blank">2N3904 datasheet</a></div> </div> <div class="info"> <a href="http://electroschematics.com/650/lm555-datasheet/" target="_blank" title="555 datasheet">555 datasheet</a></div>

Wide Frequency Range 555 VCO

The 555 frequency can be varied via adjusting the voltage at pin 5. However, the range and linearity of frequency adjustment is very limi...

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Quirky 555 Timer Reset Function

How many have had legitimate problems with the 555 timer? Let me guess…it involved the reset line, did it not? We all know that pin 4 must be set high before oscillation begins, but what is its threshold? input current? and what happens when it is operated slightly out of spec? This may be the very first attempt in documentation of this obscure phenomenon.<br /> <span id="more-7195"></span><br /> <ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_0_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins><br /> <span style="font-size: large;"><b>555 pin 4 reset behavior schematic</b></span><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Test-Circuit-1.jpg" target="_blank"><img alt="555 pin 4 reset behavior Test Circuit 1" class="alignnone size-large wp-image-7201" height="318" src="http://electroschematics.com/wp-content/uploads/2012/12/Test-Circuit-1-550x318.jpg" title="" width="550" /></a><br /> <b>Method</b><br /> To determine reset threshold, a transistor integrator generates a low impedance, negative-going ramp voltage signal that integrates from +5V to –0.65V. To obtain the negative voltage, the power supply is split to provide –0.7V. While it is slowly changing at the rate of -1V /S (trace 1), pins 2 & 6 are monitored for oscillation (trace 2). A 3rd trace monitors the output (pin 3). All data is logged on the spreadsheet.<br /> A total of (8) devices were tested, including (2) CMOS TLC555N devices.<br /> When running, the 555 oscillates at approx. 100hZ. Vcc = 5V.<br /> <b>Data</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Data.jpg" target="_blank"><img alt="" class="alignnone size-large wp-image-7198" height="184" src="http://electroschematics.com/wp-content/uploads/2012/12/Data-550x184.jpg" title="Data" width="550" /></a><br /> <b>Oscillograph</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/555-Pin-4-Oscillograph.jpg" target="_blank"><img alt="" class="alignnone size-full wp-image-7196" height="408" src="http://electroschematics.com/wp-content/uploads/2012/12/555-Pin-4-Oscillograph.jpg" title="555 Pin 4 Oscillograph" width="498" /></a><br /> <b>Observations</b><br /> The threshold voltage is exceptionally low—lower than any true logic device. Specifications indicate a threshold range of 0.4 to 1.0V in bipolar devices, and 0.4 to 1.5V in CMOS device. Actual measurements indicate a range of 0.65 to 0.75V (bipolar) and 1.1V (CMOS).<br /> What is most interesting is what happens when the voltage drops a little below –0.12V. At this voltage, pin 7 turns off and the voltage at pins 2 & 6 floats high while pin 3 demonstrates an abnormally high saturation voltage (0.8V)—normal is 0.1V. While this is an out-of-spec condition, it remains important information to know because it occurs very close to zero volts and may be subject to noise. <br /> In some cases, this anomaly can actually occur above 0V. I recall from years ago some 555’s that exhibited this behavior at approx +20mV. The solution at the time was the addition of a series resistor in the reset line. Of course these devices were out of spec and therefore defective according to published specifications. Since then, I think manufacturers have been testing for this specific condition. I challenge readers to locate some of these strange 555’s and make comment—very simple to test for this condition by simply shorting pin 4 to common and see if pin 7 allows capacitor voltage to float up.<br /> One of the CMOS devices actually started to oscillate again at -0.65V. I have had issues with this chip before, so I think that I can write it off as defective—may have taken a static discharge…<br /> <b>Not recommended as a voltage threshold function input</b><br /> Due to the extremely low and variable threshold, the reset line must not be used as an input level threshold. I know it is used this way in numerous electroschematics.com circuits, but I cannot recommend it—this may be an explanation why some circuits fail to operate.<br /> <b>Looks good on paper, but this is an out of spec condition</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Test-Circuit-3.jpg" target="_blank"><img alt="" class="alignnone size-large wp-image-7203" height="327" src="http://electroschematics.com/wp-content/uploads/2012/12/Test-Circuit-3-550x327.jpg" title="Test Circuit 3" width="550" /></a><br /> This is a typical interface to avoid—looks clean and simple and works with most logic interfaces, but does not work with the 555. What a simulator would show? A simulator cannot handle out of spec conditions.<br /> <b>Another way to preset /reset the 555</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Test-Circuit-2.jpg" target="_blank"><img alt="" class="alignnone size-large wp-image-7202" height="336" src="http://electroschematics.com/wp-content/uploads/2012/12/Test-Circuit-2-550x336.jpg" title="Test Circuit 2" width="550" /></a><br /> Open collector comparators etc. work well as an interface to the 555.<br /> <b>Input current</b><br /> Reset current maxed out at 0V. Actual range was -13 to -33uA. The minus sign indicates that current comes out of pin 4 (sourced) as opposed to going into the pin (sinked). CMOS input current was understandably immeasurable. Actual specification for the bipolar version is 400uA typical. From this data you can determine what you need to drive it below the reset threshold voltage—Max series resistor value must not generally exceed 470Ω or so.<br /> <b>Photos</b><br /> <br /> <div class="ngg-galleryoverview" id="ngg-gallery-8-7195"> <div class="ngg-gallery-thumbnail-box" id="ngg-image-54"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_8" href="http://electroschematics.com/wp-content/gallery/quirky-555-timer-reset-function/bench-setup.jpg" title=" "> <img alt="bench setup" height="75" src="http://electroschematics.com/wp-content/gallery/quirky-555-timer-reset-function/thumbs/thumbs_bench-setup.jpg" title="bench setup" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-55"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_8" href="http://electroschematics.com/wp-content/gallery/quirky-555-timer-reset-function/protoboard-setup.jpg" title=" "> <img alt="protoboard setup" height="75" src="http://electroschematics.com/wp-content/gallery/quirky-555-timer-reset-function/thumbs/thumbs_protoboard-setup.jpg" title="protoboard setup" width="100" /> </a> </div> </div> </div> <b>For the future</b><br /> Quirky <a href="http://electroschematics.com/628/lm358-datasheet/" title="LM358">LM358</a> /LM324 /LM293 /LM339 common mode input range issues<br /> <b>Glossary of undocumented words and idioms</b> (for our ESL friends)<br /> write it off –idiom—consider defective—forget it—give up on that idea…<br /> <b>Recommended devices for the serious experimenter</b><br /> <div class="sectiune"> <a href="http://electroschematics.com/wp-content/uploads/2012/12/DIP-8.jpg" target="_blank"><img alt="" class="alignleft size-thumbnail wp-image-7199" height="100" src="http://electroschematics.com/wp-content/uploads/2012/12/DIP-8-100x100.jpg" title="DIP-8" width="100" /></a><br /> LM555CN<br /> DIP-8 Package<br /> DigiKey LM555CNFS-ND, $0.43 each <br /> <div class="info"> <a href="http://electroschematics.com/650/lm555-datasheet/" target="_blank">LM555 datasheet</a></div> </div> <div class="sectiune"> <a href="http://electroschematics.com/wp-content/uploads/2012/12/DIP-8.jpg" target="_blank"><img alt="" class="alignleft size-thumbnail wp-image-7199" height="100" src="http://electroschematics.com/wp-content/uploads/2012/12/DIP-8-100x100.jpg" title="DIP-8" width="100" /></a><br /> TLC555CP<br /> DIP-8 Package, CMOS<br /> DigiKey 296-1857-5-ND, $0.74 each <br /> <div class="info"> <a href="http://electroschematics.com/650/lm555-datasheet/" target="_blank">TLC555 datasheet</a></div> </div>

Quirky 555 Timer Reset Function

How many have had legitimate problems with the 555 timer? Let me guess…it involved the reset line, did it not? We all know that pin 4 mu...

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LDR Pole Light Switch

My vintage (62 year old) pole light has always been controlled by a timer—a source of continual frustration due the requirement of readjustment for the ever-changing seasons. However, after knocking it over (I backed my car into it…), I decided it was time for an update. The circuit consists of a light dependent resistor (LDR), TLC555 (applied as Schmitt trigger), and a TRIAC power switch. The complete assembly neatly fits inside the steel pole light tube and the LDR peeks out through a hole in the side. This was really a fun project, and useful to boot.<br /> <span id="more-7207"></span><br /> <ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_0_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins><br /> <span style="font-size: large;"><b>Pole Light Switch Circuit Schematic</b></span><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/LDR-Pole-Light-Switch.jpg" target="_blank"><img alt="LDR Pole Light Switch Schematic" class="alignnone size-large wp-image-7219" height="275" src="http://electroschematics.com/wp-content/uploads/2012/12/LDR-Pole-Light-Switch-550x275.jpg" title="" width="550" /></a><br /> <b>Power supply</b><br /> The power supply is the typical capacitor limited charge pump type that is zener regulated at 6.2V. Due to the lack of isolation, I was careful to identify the return conductor so that the electronics (including the LDR) would not be floating on the hot lead. For safety, most of the testing was done using an isolation transformer. R1 must absorb a high peak power transient current when power is applied, so a carbon comp, ceramic comp, or wire wound resistor is recommended. Maximum DC current available is 16mA. Actual load is about 6mA. My application was 115V, 60hZ. For 230VAC, the components are indicated on the schematic. In this circuit, +6V is the power return lead, and 0V is the electronic circuit common—to visualize this, one must screw his head on backwards…<br /> <b>LDR</b><br /> The light dependent resistor (CdS photocell) that I used was in the TO-5 package that is well adapted for poking through a hole and is held in place with silicone rubber. The Clairex CL703M19 LDR that I used is no longer available and I have been unable to locate the specs. The DigiKey PDV-P8103-ND appears to be a reasonable choice, but may require bias current tweaking to set the threshold.<br /> <b>555 Schmitt trigger driver</b><br /> A TLC 555 was used as a voltage threshold detecting device with hysteresis. Pin 7 drives the TRIAC gate directly via its open collector output. This is a rather unconventional application. The CMOS version is used to minimize power supply load—I tried a bipolar 555 and it worked, but the power supply ripple voltage doubled to about 0.5VP-P.<br /> <b>Constant current bias—Threshold adjustment</b><br /> Because the 555 has so much hysteresis, I feared that the ON & OFF thresholds would be too far apart. To help reduce the hysteresis, the LDR is biased by a current source. Q1 is wired as a current source—its collector current does not vary with collector voltage. This technique essentially increases the “gain” of the LDR. The current is set via adjusting the emitter resistor (R3)—it drops about 0.37V. <br /> C3 makes the circuit insensitive to rapid changes in light intensity. It takes about 60sec to turn on.<br /> <b>Logic TRIAC</b><br /> The logic TRIAC is an interesting device. It can be triggered by either a positive or negative gate current regardless of voltage blocking polarity. For maximum sensitivity, I used negative gate current. The device I used had an actual Igt (gate current sensitivity) of 1.5mA that is well below the 5mA Max specification. However, gate overdrive (5mA in my case) is recommended to assure that it fires at low winter temperatures. Quencharc RC-1 is connected across the TRIAC to help control turn-off voltage transients.<br /> <b>Choice of lighting</b><br /> For the time being, I am sticking with the vintage incandescent lamp—it is a matter of aesthetics. I will upgrade to LED technology only when its color balance matches incandescent.<br /> <b>Photo gallery</b><br /> <div class="ngg-galleryoverview" id="ngg-gallery-9-7207"> <div class="ngg-gallery-thumbnail-box" id="ngg-image-58"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_9" href="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/getting-ready.jpg" title=" "> <img alt="Getting Ready with the pole light switch" height="75" src="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/thumbs/thumbs_getting-ready.jpg" title="Getting Ready with the pole light switch" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-57"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_9" href="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/finished-assembly.jpg" title=" "> <img alt="Finished pole light switch Assembly" height="75" src="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/thumbs/thumbs_finished-assembly.jpg" title="Finished pole light switch Assembly" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-63"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_9" href="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/test-setup.jpg" title=" "> <img alt="test setup" height="75" src="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/thumbs/thumbs_test-setup.jpg" title="test setup" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-60"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_9" href="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/installed.jpg" title=" "> <img alt="Installed pole light switch" height="75" src="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/thumbs/thumbs_installed.jpg" title="Installed pole light switch" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-61"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_9" href="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/ldr.jpg" title=" "> <img alt="LDR sensor" height="75" src="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/thumbs/thumbs_ldr.jpg" title="LDR sensor" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-56"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_9" href="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/day.jpg" title=" "> <img alt="pole light switch on day" height="75" src="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/thumbs/thumbs_day.jpg" title="pole light switch on day" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-62"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_9" href="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/night.jpg" title=" "> <img alt="night pole light switch" height="75" src="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/thumbs/thumbs_night.jpg" title="night pole light switch" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-59"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_9" href="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/gfi-convenience-outlet.jpg" title=" "> <img alt="GFI Convenience Outlet" height="75" src="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/thumbs/thumbs_gfi-convenience-outlet.jpg" title="GFI Convenience Outlet" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-64"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_9" href="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/timer-not.jpg" title=" "> <img alt="timer not" height="75" src="http://electroschematics.com/wp-content/gallery/ldr-pole-light-switch/thumbs/thumbs_timer-not.jpg" title="timer not" width="100" /> </a> </div> </div> </div> <b>For the future</b><br /> TRIAC phase control<br /> <b>Glossary of undocumented words and idioms</b> (for our ESL friends)<br /> tweaking –small adjustment (electronics)<br /> to boot –idiom—literally, to kick around—In addition to—fringe benefit—“extra spending money to boot”<br /> time being –idiom—the present time, presently, for now…<br /> <b>Preferred components for the serious experimenter</b><br /> <div class="sectiune"> <a href="http://electroschematics.com/wp-content/uploads/2012/12/2N6073.jpg" target="_blank"><img alt="" class="alignleft size-thumbnail wp-image-7208" height="100" src="http://electroschematics.com/wp-content/uploads/2012/12/2N6073-100x100.jpg" title="2N6073" width="100" /></a><br /> 2N6075B, Logic TRIAC, 4A, 600V, Igt = 3mA, TO-225AA<br /> DigiKey 2N6075BGOS-ND, $0.69 each <br /> <div class="download-pdf"> <a href="http://electroschematics.com/wp-content/uploads/2012/12/2N6071-Datasheet.pdf" target="_blank">2N6071 datasheet</a></div> </div> <div class="sectiune"> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Photocell.jpg" target="_blank"><img alt="" class="alignleft size-thumbnail wp-image-7216" height="100" src="http://electroschematics.com/wp-content/uploads/2012/12/Photocell-100x100.jpg" title="Photocell" width="100" /></a><br /> LDR (CdS Photocell), Advanced Photonics PDV-P8103<br /> DigiKey PDV-P8103-ND, $0.80 each <br /> <div class="download-pdf"> <a href="http://electroschematics.com/wp-content/uploads/2012/12/PDV-P8103-ldr.pdf" target="_blank">PDV-P8103 datasheet</a></div> </div> <div class="info"> <a href="http://electroschematics.com/7207/ldr-pole-light-switch/electroschematics.com/650/lm555-datasheet/" rel="nofollow" target="_blank">555 datasheet</a></div> <div class="info"> <a href="http://electroschematics.com/6355/ldr-light-dependent-resistor-photoresistor/" target="_blank" title="LDR = Light Dependent Resistor = Photoresistor">what is LDR</a></div>

LDR Pole Light Switch

My vintage (62 year old) pole light has always been controlled by a timer—a source of continual frustration due the requirement of readjus...

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555 Door Ajar Flasher

A magnet is placed on the door and a magnetic reed switch on the door casing so when the door is closed the circuit is disabled. When the door is open, the LED flashes VERY BRIGHTLY—when closed, the circuit is disabled in such a way that it draws virtually no current for maximum battery life.<br /> <span id="more-7233"></span><br /> <ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_0_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins><br /> <span style="font-size: large;"><b>Door Ajar LED Light Schematic</b></span><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/555-Door-Ajar-Flasher-Circuit.jpg" target="_blank"><img alt="555 Door Ajar Flasher Circuit Schematic" class="alignnone size-large wp-image-7235" height="330" src="http://electroschematics.com/wp-content/uploads/2012/12/555-Door-Ajar-Flasher-Circuit-550x330.jpg" title="" width="550" /></a><br /> <b>Bill of material </b><br /> <div class="download-archive"> <a href="http://electroschematics.com/wp-content/uploads/2012/12/555-Door-Ajar-Flasher-BOM.rar" target="_blank">555 door ajar BOM</a></div> <b>How it works</b><br /> The flasher is the standard 555 oscillator circuit that drives an ultrabright white LED for daylight visibility. Repetition rate is about 2hZ and the duty cycle is about 10%. Peak LED current is 60mA, but average is 6mA. <br /> Since the door is supposed to remain closed most of the time, the circuit power is controlled by a 2N7000 N Channel MOSFET. When the reed switch is closed (sensing the magnet), it shorts out the gate drive signal to the transistor and turns off the oscillator. At this time the battery drain is only 9uA. <br /> Note that there seems to be no convenient way to turn off the 555 in such a way that it does not draw much current. Grounding pin 4 stops oscillation, but turns on the LED continuously.<br /> C2 provides voltage transient protection for the MOSFET gate.<br /> LED brightness is controlled by R5—YIKES! do not look into the LED like I did…<br /> <b>The reed switch</b><br /> This circuit uses the commonly available NC (normally closed) reed switch. A NO variety would be easier to use, but such is rare and expensive. If the circuit is packaged inside a small plastic enclosure, the reed switch could be cemented into one edge of the box thus protecting the glass tube from damage. The reed switch I used for the test is packaged in a plastic tube. It is quite sensitive — can sense the magnet at 2 to 3cm.<br /> <b>Door Ajar Flasher Photos</b><br /> <div class="ngg-galleryoverview" id="ngg-gallery-12-7233"> <div class="ngg-gallery-thumbnail-box" id="ngg-image-71"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_12" href="http://electroschematics.com/wp-content/gallery/555-door-ajar-flasher/getting-parts-togther.jpg" title=" "> <img alt="Door Ajar Light Flasher Components" height="75" src="http://electroschematics.com/wp-content/gallery/555-door-ajar-flasher/thumbs/thumbs_getting-parts-togther.jpg" title="Door Ajar Light Flasher Components" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-70"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_12" href="http://electroschematics.com/wp-content/gallery/555-door-ajar-flasher/flasher.jpg" title=" "> <img alt="Door Ajar Light Flasher Testing" height="75" src="http://electroschematics.com/wp-content/gallery/555-door-ajar-flasher/thumbs/thumbs_flasher.jpg" title="Door Ajar Light Flasher Testing" width="100" /> </a> </div> </div> </div> <b>For the future</b><br /> 555 Strobe Circuit<br /> <div class="info"> <a href="http://electroschematics.com/650/lm555-datasheet/" target="_blank">555 datasheet</a></div>

555 Door Ajar Flasher

A magnet is placed on the door and a magnetic reed switch on the door casing so when the door is closed the circuit is disabled. When the ...

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Bicycle Anti-Theft Alarm Circuit

I hate to suggest the specific application ‘bicycle’ because it may be use to protect many items from theft. This anti-theft alarm project is built around the inexpensive Measurement Specialties DT piezo film sensor. Every now and then everything seems to work out perfectly as in the Yin and Yang of the cosmos, and this is one of them.<br /> It is simple, inexpensive and practical…<br /> <span id="more-7429"></span><br /> <ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_0_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins><br /> <span style="font-size: large;"><b>Anti-Theft Alarm Schematic</b></span><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Anti-Theft-Schematic.jpg" target="_blank"><img alt="Anti-Theft Schematic" class="alignnone size-large wp-image-7434" height="216" src="http://electroschematics.com/wp-content/uploads/2012/12/Anti-Theft-Schematic-550x216.jpg" title="" width="550" /></a><br /> <b>Bill of Material</b><br /> <div class="download-archive"> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Anti-Theft-BOM.rar" target="_blank">anti-theft BOM.xls</a></div> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Anti-Theft-BOM.jpg" target="_blank"><img alt="" class="alignnone size-large wp-image-7430" height="299" src="http://electroschematics.com/wp-content/uploads/2012/12/Anti-Theft-BOM-550x299.jpg" title="Anti-Theft BOM" width="550" /></a><br /> <b>Piezo sensor</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Piezo-Transducer.jpg" target="_blank"><img alt="" class="alignnone size-full wp-image-7438" height="356" src="http://electroschematics.com/wp-content/uploads/2012/12/Piezo-Transducer.jpg" title="Piezo Transducer" width="478" /></a><br /> I received this DT piezo film sensor as a sample years ago. It was attached to the application page via a round sticker. I never removed the sticker, but used it to attach #6 nut to increase inertia at the tip of the device—I could have experimented with other small masses, but this worked well from the git-go, so I left it that way. When the film is flexed, it produces a voltage at the terminals.<br /> <a href="http://www.meas-spec.com/downloads/DT_Series.pdf" rel="nofollow" target="_blank">http://www.meas-spec.com/downloads/DT_Series.pdf</a><br /> Initial experiments with the sensor were disappointing—I observed voltage and connected it to a charge pump type detector—yes, it functioned, but sensitivity was poor. <br /> <b>Single JFET transistor charge amplifier </b><br /> Then I read up on charge amplifiers. One good discussion is “Signal Conditioning Piezoelectric Sensors” <a href="http://www.ti.com/lit/an/sloa033a/sloa033a.pdf" rel="nofollow" target="_blank">http://www.ti.com/lit/an/sloa033a/sloa033a.pdf</a><br /> The paper discussed using FET input op amps in such a way that the sensor develops no voltage at the output terminals—only generates a current that is then amplified by the charge amplifier. This is important because the sensor has significant capacitance (e.g. 500pf) and any voltage generated by the sensor is swamped by this capacitance thus greatly attenuating the output voltage.<br /> Then the wheels started turning—and I thought up a means of using a single JFET as a charge amplifier. This I bread boarded and tested—performance was phenomenal! The source feedback resistor doubles as a negative feedback device depending upon the position of the trim pot adjustment.<br /> <b>JFET selection</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/J113-Photo.jpg" target="_blank"><img alt="" class="alignnone size-full wp-image-7435" height="283" src="http://electroschematics.com/wp-content/uploads/2012/12/J113-Photo.jpg" title="J113 Photo" width="306" /></a><br /> Unfortunately, the selection of TO-92 style JFETs is now limited, but the J111, J112 & J113 seem to be going strong. These three vary mainly in the Idss parameter (drain current with gate shorted to source). The J113 has a min Idss of 2mA that is best for our application because one goal is to minimize battery current. Since I did not have one of these devices on hand, I used an ancient MPF-106. I experimented with a total of (7) JFET devices, and only one would not work and that was because its Idss was so high that it turned itself fully on—I could have used this device by reducing the value of R3, but that would have increased battery drain. As it was, this stage consumed 160uA—similar to a low power op amp. NXP has the best J113 datasheet:<br /> <a href="http://www.nxp.com/documents/data_sheet/J111_112_113_CNV.pdf" rel="nofollow" target="_blank">http://www.nxp.com/documents/data_sheet/J111_112_113_CNV.pdf</a><br /> <b>Charge pump detector</b><br /> The charge pump detector is essentially the same as a cascade voltage doubler rectifier that is used for signal applications. It detects the peak to peak voltage of the AC input voltage waveform (minus the diode drops). In this circuit C2, C3, D1 & D2 perform this function. Additional sensitivity adjustment is possible via adjusting the value of C2. The value of C3 effects both attack and decay time.<br /> <b>Anti-Theft Alarm Oscillograph</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Anti-Theft-Oscillographs.jpg" target="_blank"><img alt="Anti-Theft Oscillographs" class="alignnone size-full wp-image-7432" height="408" src="http://electroschematics.com/wp-content/uploads/2012/12/Anti-Theft-Oscillographs.jpg" title="" width="498" /></a><br /> <b>Anti-Theft Alarm Protoboard</b><br /> <a href="http://electroschematics.com/wp-content/uploads/2012/12/Anti-Theft-Protoboard.jpg" target="_blank"><img alt="anti theft alarm photoboard" class="alignnone size-large wp-image-7433" height="412" src="http://electroschematics.com/wp-content/uploads/2012/12/Anti-Theft-Protoboard-550x412.jpg" title="" width="550" /></a><br /> <b>555 voltage threshold detector/pulse generator</b><br /> You may recall that in a previous article, I did not recommend using pin 4 as a level detector.<br /> <a href="http://electroschematics.com/7195/quirky-555-timer-reset-function/" target="_blank">http://electroschematics.com/7195/quirky-555-timer-reset-function/</a><br /> However, I should have qualified it to allow the TLC555 CMOS device manufactured by TI. This device works well in this application with its low reset threshold (1.1V) and very high input impedance.<br /> Wired as an astable multivibrator, the external components draw no additional current when in the reset condition. With a repetition rate of 2hZ, it gets maximum attention.<br /> The TLC 555 is unable to source the required load of 28mA, so a 2N4401 provides the additional drive capability.<br /> <b>Battery operation</b><br /> Idle current is about 300uA. Theft alarm mode current is about 28mA. This lends itself well to long 9V alkaline battery life. Furthermore, when the key switch is off, drain is zero.<br /> <b>Physical construction</b><br /> <br /> <div class="ngg-galleryoverview" id="ngg-gallery-14-7429"> <div class="ngg-gallery-thumbnail-box" id="ngg-image-74"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_14" href="http://electroschematics.com/wp-content/gallery/bicycle-anti-theft-alarm/keyswitch.jpg" title=" "> <img alt="keyswitch" height="75" src="http://electroschematics.com/wp-content/gallery/bicycle-anti-theft-alarm/thumbs/thumbs_keyswitch.jpg" title="keyswitch" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-75"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_14" href="http://electroschematics.com/wp-content/gallery/bicycle-anti-theft-alarm/piezo-buzzer.jpg" title=" "> <img alt="piezo-buzzer" height="75" src="http://electroschematics.com/wp-content/gallery/bicycle-anti-theft-alarm/thumbs/thumbs_piezo-buzzer.jpg" title="piezo-buzzer" width="100" /> </a> </div> </div> <div class="ngg-gallery-thumbnail-box" id="ngg-image-76"> <div class="ngg-gallery-thumbnail"> <a class="shutterset_set_14" href="http://electroschematics.com/wp-content/gallery/bicycle-anti-theft-alarm/plastic-box.jpg" title=" "> <img alt="plastic-box" height="75" src="http://electroschematics.com/wp-content/gallery/bicycle-anti-theft-alarm/thumbs/thumbs_plastic-box.jpg" title="plastic-box" width="100" /> </a> </div> </div> </div> <br /> Note this is something that I did not build, but this is how I would do it. The plastic box is indicated on the BOM. It may be attached to the bicycle frame via two cable ties that pass through holes in the box (either cover or box may be made stationary). If higher security is desired, cut slots in the box and use small stainless steel hose clamps with the buckle located inside the box where it is inaccessible—getting it all to fit may be a challenge. The LEDs are located on the left and right sides to obtain maximum attention—with the correct hole diameter, the LEDs are a press fit.<br /> The key switch may be scavenged from an old desktop computer (if you can locate one with the key). They are also available on eBay at a very reasonable price (new)—used ones are expensive.<br /> <b>Glossary of undocumented words and idioms</b> (for our ESL friends)<br /> git-go –idiom, noun, variation of get-go –from the beginning or outset—although not indicated, I think that it was derived from the old animal handling (horse) phrase “giddy up”<br /> wheels started turning –idiom, started to think<br /> <div class="info"> <a href="http://electroschematics.com/7429/bicycle-anti-theft-alarm-circuit/electroschematics.com/650/lm555-datasheet/" rel="nofollow" target="_blank">555 datasheet</a></div>

Bicycle Anti-Theft Alarm Circuit

I hate to suggest the specific application ‘bicycle’ because it may be use to protect many items from theft. This anti-theft alarm project...

Read more »