12V To 24V DC-DC Converter Circuit

This simple DC-DC converter can provide up to 24V from a 12V source. It can be used to run radios, small lights, relays, horns and other 24V accessories from a 12V vehicle with a maximum draw of about 800mA. It can be used to charge one 12V battery from another, or step up the voltage just enough to provide necessary overhead for a 12V linear regulator. Using one op-amp as a squarewave oscillator to ring an inductor and another op-amp in a feedback loop, it won't drift around under varying loads, providing a stable 24V source for many applications. With a wide adjustment in output this circuit has many uses.

Schematic

Parts

Part Total Qty. Description Substitutions R1, R2, R3, R4, R8, R7 6 100K 1/4W Resistor R5 1 470 Ohm 1/2W Resistor R6 1 10K Linear Pot C1 1 0.01uF Mylar Capacitor C2 1 0.1uF Ceramic Disc Capacitor C3 1 470uF 63V Electrolytic Capacitor D1 1 1N4004 Rectifier Diode D2 1 BY229-400 Fast Recovery Diode See Notes Q1 1 BC337 NPN Power Transistor U1 1 LM358 Dual Op Amp IC L1 1 See Notes MISC 1 Board, Wire, Socket For U1, Case, Knob For R6, Heatsink for Q1

Notes

1. R6 sets the output voltage. This can be calculated by Vout = 12 x (R8/(R8+R7)) x (R6B/R6A).
2. L1 is made by winding 60 turns of 0.63MM magnet wire on a toroidial core measuring 15MM (OD) by 8MM (ID) by 6MM (H).
3. D2 can be any fast recovery diode rated at greater then 100V at 5A. It is very important that the diode be fast recovery and not a standard rectifier.
4. Q1 will need a heatsink.

Wire Loop Alarm

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 100K 1/2W 1% Resistor R2, R4 2 10K 1/2W 1% Resistor R3 1 1 Meg 1/2W 1% Resistor C1, C3 2 0.1uF Ceramic Disc Capacitor C2 1 0.01uF Ceramic Disc Capacitor IC1 1 4001UBE Quad 2-i/p NOR Gate Q1 1 MPSA14 Low Power NPN Transistor SIREN 1 Micro piezo siren 12V DC 150mA, 110dB @ 1M LOOP 1 See "Notes" MISC 1 Board, Wire, Socket For IC1

Notes

1. Email Alex Meaden with questions, comments, etc.
2. The loop can be any type of hookup wire, with a maximum resistance of about 90K. Using very thin wire (40AWG, for example) will make a very sensitive trip wire, but will shorten the distance it can be strung due to the high resistance.
3. The siren can be replaced with a relay to drive external loads.

Water Detector With Sump/Bilge Pump Controller

This moisture detector with pump controller is built around the special purpose LM1830 IC. The LM1830 is designed to detect moisture by passing an AC current through a set of probes. An internal comparator compares the resistance of the probes to an internal reference. When the resistance between the probes is low (indicating the presence of water or other conductive liquid) then the IC triggers it's output. An AC signal avoids electroplating and corrosion problems that are common when DC is used. To provide an adjustable delay hysteresis to avoid cycling the pump, a timer based around the 555 is used a range of about 5 seconds to two minutes. In this way the pump will stay active for a set amount of time even if the fluid level is below that of the probes.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 470 Ohm 1/4 W Resistor R2, R4 1 10K 1/4 W Resistor R3 1 6.8K 1/4 W Resistor R5 1 1 Meg Linear Taper Pot R6 1 51K 1/4 W Resistor C1 1 470uF 35V Electrolytic Capacitor C2 1 0.001uF Ceramic Disc Capacitor C3 1 0.05 uF Ceramic Disc Capacitor C4 1 20uF 35V Electrolytic Capacitor C5 1 6.8uF 35V Electrolytic Capacitor C6, C8 2 0.01uF Ceramic Disc Capacitor C7 1 100uF 35V Electrolytic Capacitor U1 1 LM1830 Fluid Detection IC U2 1 555 Timer Q1 1 2N5305 NPN Power Transistor D1, D2 2 1N4148 Signal Diode D3 1 1N4002 Rectifier Diode K1 1 Relay With 12V Coil (See Notes) S1 1 SPST Switch PROBES 1 Stainless Steel Probes (See Notes) MISC 1 Case, Knob, Board, Wire, Sockets For U1 and U2

Notes

1. The probes should be made of stainless steel and mounted in a non-conductive fixture. Stainless steel nails, bolts or welding rod will make ideal probes. Good non-conductive materials are Lexan, plexiglass or plastic. The probes are to be placed at the liquid level at which you wish the pump to turn on.
2. K1 should be chosen according to the requirements of the pump. If you are running a 12V pump then common automotive relays will work fine. If you are running a mains powered pump then you will need to make sure the contacts are rated accordingly.
3. S1 provides a manual pump switch.
4. R5 adjusts the on-time of the pump once moisture has been detected. It is adjustable from approximately 5 seconds to approximately 2 minutes.
5. The probes should be cleaned periodically to assure reliable operation.

Video Stabilizer/MacroVision Removal

Have you ever attempted to copy a commercially produced video only to end up with a distorted and jumpy image? If so, then you have run afoul of MacroVision. MacroVision is the most popular copy protection scheme used on the majority of content distributed on VHS cassettes. Like all copy protection, it does nothing to discourage the real pirates and only annoys the user who may wish to create a legal copy for backup and archival purposes. This circuit can eliminate MacroVision encoding in both NTSC and PAL recordings.

Schematic

Parts

Part Total Qty. Description Substitutions R1, R2, R3, R4, R5, R7 6 68K 1/4W Resistor R6 2 75 Ohm 1/4W Resistor R8, R9 2 100 Ohm 1/4W Resistor R10 1 2.2K 1/4W Resistor R11 1 1.5K 1/4W Resistor R12, R17 2 470K 1/4W Resistor R13, R16 2 33K 1/4W Resistor R14 1 6.8K 1/4W Resistor R15 1 22K 1/4W Resistor R18 1 47K 1/4W Resistor C1 1 15uF Electrolytic Capacitor C2 1 220uF Electrolytic Capacitor C3 1 220pF Ceramic Disc Capacitor C4 1 0.0022uF Ceramic Disc Capacitor C5, C7, C8, C9, C10, C11, C12, C13 7 0.1uF Ceramic Disc Capacitor C6 1 0.47uF Ceramic Disc Capacitor D1-D9, D10-D18, D19-D27, D28, D29, D30, D31, D32, D33, D34, D35 35 1N4148 Diode Q1 1 BC548 NPN Transistor Q2 1 BC558 PNP Transistor U1 1 4040 12-Bit Ripple Counter U2, U3 2 4027 Dual J-K Flip Flop U4 1 4011 Quad Two Input NAND Gate U5 1 TL802 Dual Op Amp U6 1 4053 Triple Two Channel Multiplexer U7 1 4069 Hex Inverter J1-J9, J10-J18, J19-J27 27 Jumper J28, J29 2 RCA Jack MISC 1 PC Board, Wire, Sockes For ICs

Notes

1. The circuit was submitted via email by Jari Ekstrom. Jari noted that the author is Antti Paarlahti and that the circuit originally came from the author's website. This website is no longer accessible. However, some searching revealed that the author of the circuit also wrote The MacroVision FAQ. The email address listed for the author in the FAQ is invalid and the FAQ was last updated in late 1996. This circuit reproduced here without permission.
2. Before use, the circuits's jumper need to be set. Take a look at the table below:
   

   MacroVision Type	Upper Start Line	Upper End Line	Lower Start Line
   PAL	0x05	0x0F	0x126
   NTSC	0x06	0x0E	0xFB

   
   To set the jumpers, first convert the line numbers to binary. You will end up with three binary digits, one for each set of line numbers. Bit 0 is least significant, bit 8 is most significant. Now simply open the jumpers at the 0 bits and close the jumpers at the 1 bits.
3. Connect your video source to "Composite Video In". As the label suggests, this circuit accempts composite video signals only. The corrected video signal is sent to the "Composite Video Out" jack.
4. With the two "Video" terminals disconnected the circuit passes video through without modifying it. Jumping the "Video" terminals enables the MacroVision removal.
5. As with all circuits involving CMOS (4000 series) ICs, you must tie the unused inputs of those ICs to ground. This is not shown on the schematic for clarity.
6. Supply voltage is 12V.

Video Activated Relay

Schematic

Parts

Part Total Qty. Description Substitutions R1, R2 2 10K 1/4 W Resistor R3 1 1K 1/4 W Resistor R4 1 33K 1/4 W Resistor C1 1 1uF Electrolytic Capacitor Q1, Q2, Q3 3 2N2222 NPN Transistor 2N3904 NPN Transistor D1, D2, D3 4 1N4148 Diode K1 1 9V Relay J1 1 RCA Jack MISC 1 Case, wire, board

Notes

1. Since you may be using this circuit to switch mains voltage, it should be enclosed in a case.
2. The circuit will also work with most line level audio, although you may have to adjust the value of R1.

Touch Switch

A touch switch is a switch that is turned on and off by touching a wire contact, instead of flicking a lever like a regular switch. Touch switches have no mechanical parts to wear out, so they last a lot longer than regular switches. Touch switches can be used in places where regular switches would not last, such as wet or very dusty areas.

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 10uF 16V Electrolytic Capacitor R1, R2 2 100K 1/4 Watt Resistor R3 1 10 Meg 1/4 Watt Resistor U1 1 4011 CMOS NAND Gate IC MISC 1 Board, Wire, Socket For U1

Notes

1. The contacts an be made with just two loops of wire close together, or two squares etched close together on a PC board.
2. When activated, the output of the circuit goes high for about one second. This pulse can be used to drive a relay, transistor, other logic, etc.
3. You can vary the length of the output pulse by using a smaller or larger capacitor for C1.

Time Delay Relay II

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 See Notes R1 1 See Notes D1 1 1N914 Diode U1 1 4011 CMOS NAND Gate IC K1 1 6V Relay S1 1 Normally Open Push Button Switch MISC 1 Board, Wire, Socket For U1

Notes

1. Email jawaharlal@excite.com with comments, questions, etc.
2. To calculate the time delay, use the equation R1 * C1 * 0.85=T, where R1 is the value of R1 in Ohms, C1 is the value of C1 in uF, and T is the time delay in seconds.
3. S1 may be replaced with an NPN transistor so the circuit can be triggered by a computer, other circuits, etc.
4. Most any 6V relay will work for K1. If you use a large relay, you my need to add a transistor to the output of the circuit in order to drive the larger load.

Time Delay Relay

A time delay relay is a relay that stays on for a certain amount of time once activated. This time delay relay is made up of a simple adjustable timer circuit which controls the actual relay. The time is adjustable from 0 to about 20 seconds with the parts specified. The current capacity of the circuit is only limited by what kind of relay you decide to use.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 1 Meg Pot R2 1 10 K 1/4 Watt Resistor C1 1 10uf 25V Electrolytic Capacitor C2 1 0.01uf Ceramic Disc Capacitor D1,D2 2 1N914 Diodes U1 1 555 Timer IC RELAY 1 9V Relay S1 1 1A 120V SPST Switch MISC 1 Board, Wire, Socket For U1

Notes

1. R1 adjusts the on time.
2. You can use a different capacitor for C1 to change the maximum on time.
3. S1 is used to activate the timing cycle. S1 can be replaced by a NPN transistor so that the circuit may be triggered by a computer, other circuit, etc.

Stepper Motor Controller

I found this circuit in my files. I don't know where it came from, but it looks like I photocopied it from somewhere years ago. I have been told that it came from "The Robot Builder's Bonanza", by Gordan McComb. Anyway, I thought that it should be fairly useful, so I decided to post it here. The circuit is very simple and inexpensive. This is good thing because most commercial stepper motor controller ICs are quite expensive. This circuit is built from standard components and can easily be adapted to be controlled by a computer. If you use cheap surplus transistors and stepper motor, the price of the circuit can be kept to under $10.

Schematic

Parts

Part Total Qty. Description Substitutions R1, R2 ,R3, R4 4 1K 1/4W Resistor D1, D2, D3, D4 4 1N4002 Silicon Diode Q1, Q2, Q3, Q4 4 TIP31 NPN Transistor (See Notes) TIP41, 2N3055 U1 1 4070 CMOS XOR Integrated Circuit U2 1 4027 CMOS Flip-Flop S1 1 SPDT Switch MISC 1 Case, Board, Wire, Stepper Motor

Notes

1. You should be able to substitute any standard (2N3055, etc.) power transistor for Q1-Q4.
2. Every time the STEP line is pulsed, the motor moves one step.
3. S1 changes the motors direction.

Simple Two Speed Contactor DC Motor Controller

The simplest of all motor controllers (besides a straight on/off switch) is the contactor controller. I designed this contactor controller for use in my electric scooter project. It is based around three 12V relays, two 12V batteries, two switches and of course a motor. Having no silicon to "fry", it is quite reliable and robust. A contactor controller works by rearranging the two (or more) supply batteries between series and parallel. This gives the motor a slow speed (batteries in parallel, current adds) and a fast speed (batteries in series, voltage adds). This assures that both batteries are discharged equally. When the circuit is "at rest", the batteries are connected in parallel, which allows easy recharging.

Schematic

Parts

Part Total Qty. Description Substitutions K1, K2, K3 3 12V 30A SPDT Relay (See Notes) S1, S2 2 SPST Switch or Button B1, B2 2 12V Battery (See Notes) M1 1 12V or 24V Motor (See Notes) MISC 1 Case, Wire, etc.

Notes

1. S1 closes K3 and thus causes M1 to operate. S2 activates K1 and K2, reconfiguring the batteries for series operation and thus causes M1 to operate at "fast" speed.
2. B1 and B2 should be chosen based on the current requirements of M1. Often, sealed lead-acid type batteries are available at local suppliers for surprisingly low prices. These batteries are ideal for things such as scooters, go-karts, etc.
3. The relays are standard automotive type relays, available cheaply from any auto parts store.
4. Your motor will depend on your requirements. 12V motors will normally run fine at 24V, and vice versa.
5. You will notice that in series mode, all three relays only pull power from B2. This is because the relays have 12V coils, and it is impossible to switch the batteries from series to parallel and keep power to the coils at the same time. This does, however, mean that B2 is discharged slighty before B1. This should normally not be an issue unless the batteries are being drained completely "dead". Draining a battery dead is not good for it in any situation, and should be avoided. If you wish, you can use a small 12V battery to run the relays separately.
6. You can add two more speeds to this controller using the schematic below. It connects at points A and B shown above on the controller schematic.
   K1 is simply another of the same relay as used in the controller. S1 is another switch. R1 needs to be chosen based on your motor, but it will be of low value (under 10 Ohm) and high wattage (normally at least 100W). It must be capable of handling the full current drawn by the motor. This is not exactly an efficient way to limit current to the motor as excess current is dissipated as heat by the resistor, so it is normally only used for a "starter" speed.

Simple Touch Switch Circuit

Similar to the CMOS based Touch Switch also on this site, this transistor based touch switch can activate a load simply by the user touching a metal plate. It is designed to directly switch a relay to allow it to be used with large loads. As it uses only a few commonly available transistors and a 12V supply, it is ideal for hostile environments where mechanical switches would be damaged. Using a latching relay and two of these circuits, a simple two pad "touch on/touch off" arrangement can be made.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 10 Meg 1/4W Resistor R2 1 47K 1/4W Resistor R3 1 120k 1/4W Resistor R4 1 470 Ohm 1/4W Resistor C1 1 15uF Electrolytic Capacitor D1 1 1N4007 Silicon Rectifier Diode Q1 1 2N5458 N Channel Field Effect Transistor Q2 1 2N2222 NPN Transistor 2N3904 Q3 1 2N3906 PNP Transistor K1 1 Relay w/12V Coil, Contacts To Suit Application MISC 1 Board, Wire, Small Metal Pad For Touch Pad

Notes

1. The touch pad can be most easily made by cutting a small square of PCB material and then soldering on a single wire. Alternatively, something like a penny glued to a plastic backing will do the job.
2. As mentioned, a latching relay can be used so that a momentary touch activates the relay and it remains active. To turn off a latching relay, power must be interrupted. So a 2nd circuit with a normal relay can be used to cut power (use the NC contacts on the 2nd circuit). Placed side by side, two touch pads form an "on" and an "off" pad

Simple Servo Controller

Servo motors have many uses in everything from robotics to puppetry to photography and beyond. These little motors can position their output shaft to any position on command and hold that position. Most servos have a range of motion to about 210 degrees and thankfully are very easy to control with a simple circuit such as the one presented here. Using just a 555 timer and a few support components this circuit can control a servo through it's full rotation based on the position of a pot. This circuit was originally published in the Think Tankcolumn of the October 1995 issue of Popular Electronics.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 820 Ohm 1/4W Resistor R2 1 68K 1/4W Resistor R3 1 10K 1/4W Resistor R4 1 1K 1/4W Resistor R5 1 1K Linear Taper Pot C1 1 1uF 16V Electrolytic Capacitor Q1 1 2N3904 NPN Transistor 2N2222, Most Small Signal Transistors U1 1 555 Timer IC MISC 1 Board, Wire, Knob For R1, 8 Pin Socket For U1

Notes

1. R1 adjusts the position of the servo.
2. Connect the servo to the circuit as shown in the schematic. For common Futaba servos, the red wire is power, the black wire is ground, and the white wire is control.

Simple Polarity Tester

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 1K 1/4W Resistor D1 1 Green LED D2 1 Red LED D4, D5, D6, D7 4 1N4001 Silicon Diode 1N4004, 1N4005, 1N4007 MISC 1 Board, Wire, Case, Probes

Notes

1. Email Dudley LeRoux with questions, comments, etc.
2. To use the circuit, just connect your probes to the source under test. If D1 lights up, the left most probe (on the schematic) is connected to positive. The opposite is true if the left probe is negative. If both LEDs are on, the source being probed is AC.
3. Be careful when using this tester not to probe a source greater than about 12V.

Light/Dark Detector

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 100K Pot Q1 1 2N3904 NPN Transistor 2N2222 Q2 1 NPN Phototransistor RELAY 1 9V Relay MISC 1 Board, Wire, 9V Battery Snap (if battery used), Knob For R1

Notes

1. R1 Adjusts sensitivity

Simple Lie Detector

Here's a simple lie detector that can be built in a few minutes, but can be incredibly useful when you want to know if someone is really telling you the truth. It is not as sophisticated as the ones the professionals use, but it works. It works by measuring skin resistance, which goes down when you lie.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 33K 1/4W Resistor R2 1 5K Pot R3 1 1.5K 1/4W Resistor C1 1 1uF 16V Electrolytic Capacitor Q1 1 2N3565 NPN Transistor M1 1 0-1 mA Analog Meter MISC 1 Case, Wire, Electrodes (See Nots)

Notes

1. The electrodes can be alligator clips (although they can be painful), electrode pads (like the type they use in the hospital), or just wires and tape.
2. To use the circuit, attach the electrodes to the back of the subjects hand, about 1 inch apart. Then, adjust the meter for a reading of 0. Ask the questions. You know the subject is lying when the meter changes.

Rain Detector

This circuit uses a sensor made of a small piece of etched PC board and a simple SCR circuit to detect rain and sound a buzzer. The SCR could also be used to activate a relay, turn on a lamp, or send a signal to a security system.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 1K 1/4 W Resistor R2 1 680 Ohm 1/4 W Resistor D1 1 1N4001 Silicon Diode BZ1 1 12V Buzzer S1 1 SPST Switch SCR1 1 C106B1 SCR 106CY SENSOR 1 See Notes MISC 1 Board, Wire, Case, PC Board (For Sensor)

Notes

1. The sensor is a small piece of PC board etched to the pattern showen in the schematic. The traces should be very close to each other, but never touching. A large spiral pattern would also work.
2. Make sure to use a loud buzzer.

Pulse Width Modulation DC Motor Control

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 1 Meg 1/4W Resistor R2 1 100K Pot C1 1 0.1uF 25V Ceramic Disc Capacitor C2 1 0.01uF 25V Ceramic Disc Capacitor Q1 1 IRF511 MOSFET IRF620 U1 1 4011 CMOS NAND Gate S1 1 DPDT Switch M1 1 Motor (See Notes) MISC 1 Case, Board, Heatsink, Knob For R2, Socket For U1

Notes

1. R2 adjusts the speed of the oscillator and therefore the speed of M1.
2. M1 can be any DC motor that operates from 6V and does not draw more than the maximum current of Q1. The voltage can be increased by connecting the higher voltage to the switch instead of the 6V that powers the oscillator. Be sure not to exceed the power rating of Q1 if you do this.
3. Q1 will need a heatsink.
4. Q1 in the parts list can handle a maximum of 5A. Use the IRF620 for 6A, if you need any higher.
5. This circuit is not a true pulse width modulation control. Because only the frequency of pulses varies, it is really pulse frequencymodulation. This works, though not as well as true PWM.

Pine Racecar Victory Judge

Schematic

Parts

Part Total Qty. Description Substitutions R1, R2 2 100 Ohm 1/4W Resistor R3, R4 2 100K 1/4W Resistor D1, D2 2 Standard LED SCR1, SCR2 2 6A, 200V SCR (such as the 106B) S1, S2 2 See Notes K1 1 Small 12V Relay MISC 1 Board, Wire

Notes

1. S1 and S2 are small lever type micro switches. Most any kind will do, as long as they are sensitive enough to be activated by the wheels of the cars. They should be positioned on the track so that the front wheels of the cars will run over them as the cars just cross the finish line.
2. To reset the circuit, disconnect and then reconnect power. You can add a normally closed switch in series with the power supply to make this easier.
3. There is no reason this circuit cannot be used to tell the winner of a foot race, bike race, slot car race, etc.

Low Voltage Alarm

Schematic

Parts

Part Total Qty. Description Substitutions R1, R3 2 1K 1/4W Resistor R2 1 5K Pot U1 1 LM339 Op Amp IC D1 1 1N5233B Zener Diode D2 1 LED BZ1 1 Piezo Buzzer MISC 1 Board, wire, socket for IC

Notes

1. The circuit will operate from 9V to 12V.
2. Adjust R2 until the alarm goes off at the correct voltage.

Digital Keypad Combination Lock

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 1uF 25V Electrolytic Capacitor C2 1 220uF 25V Electrolytic Capacitor R1 1 2.2K 1/4W Resistor Q1 1 2N3904 NPN Transistor 2N2222 D1 1 1N4148 Rectifier Diode 1N4001-1N4007 K1 1 12V SPDT Relay Any appropriate relay with 12V coil U1 1 LS7220 Digital Lock IC S1-S12 12 SPST Momentary Pushbutton Keypad (see notes) HD1 1 12 Position Header

Notes

1. To set the combination, wire the appropriate switches to U1 pins 3, 4, 5 and 6 using the header. For example if S1 was connected to pin 3, S2 to pin 4, S3 to pin 5 and S4 to pin 6, the combination would be 1,2,3,4. Now wire all other unused switches across the header to pin 2 of U1. In this way you can create any 4 digit combination you want. Pin 2 is the reset pin, so connecting all unused keys to it assures that the entire combination must be reentered if an incorrect key is pressed.
2. When the appropriate combination is entered, the relay is activated for a period of time determined by C1. The 1uF capacitor specified in the parts list will result in an on-time of roughly 5 seconds. Increase the value of C1 to increase this time.
3. An easy way to make a keypad is to buy 12 PC board mount pushbuttons and then etch a PC board so that the buttons are in 4 rows of 3, similar to a telephone keypad. Place this in a case and then use a label maker or transfer letters to add your numbers to the tops of the pushbuttons. You can also use a pre made keypad but keep in mind that you need a pad which provides an output for each key. Most pads available have the keys connected to provide a row and column signal when they are pressed.