• 3x3x3 LED Cube Circuit

    This circuit drives a 3x3x3 cube consisting of 27 white LEDs. The 4020 IC is a 14 stage binary counter and we have used 9 outputs. Each output drives 3 white LEDs in series and we have omitted a dropper resistor as the chip can only deliver a maximum of 15mA per output. The 4020 produces 512 different patterns before the sequence repeats and you have to build the project to see the effects it produces on the 3D cube.
  • 555 Amplifier Circuit

    The 555 can be used as an amplifier. It operates very similar to pulse-width modulation. The component values cause the 555 to oscillate at approx 66kHz and the speaker does not respond to this high frequency.  Instead it responds to the average CD value of the modulated output and demonstrates the concept of pulse-width modulation. The chip gets very hot and is only for brief demonstrations.

    This circuit uses a mixture of transistors, an IC and a relay and is used to automatically open and close a pair of curtains. Using switch S3 also allows manual control, allowing curtains to be left only partially open or closed. The circuit controls a motor that is attached to a simple pulley mechanism, to move the curtains.
    Automatic Operation
    The circuit can be broken into three main parts; a bi-stable latch, a timer and a reversing circuit. Toggle switch S3 determines manual or automatic mode. The circuit as shown above is drawn in the automatic position and operation is as follows. The bi-stable is built around Q1 and Q2 and associated circuitry and controls relay A/2. S1 is used to open the curtains and S2 to close the curtains. At power on, a brief positive pulse is applied to the base of Q2 via C2. Q2 will be on, and activate relay A/2.
    The network of C3 and R4 form a low current holding circuit for the relay. Relay A/2 is a 12V relay with a 500 ohm coil. It requires slightly less current to keep it energized than it does to operate it. Once the relay has operated, the current through the coil is reduced by R4, saving power consumption. When Q2 is off, C3 will be discharged, but when Q2 becomes active (either at switch-on or by pressing S1) capacitor C3 will charge very quickly via the relay coil. The initial charging current is sufficient to energize the relay and current flow through R4 sufficient to keep it energized.
  • Bike Turning Signal Circuit

    This circuit can be used to indicate left and right turn on a motor-bike. Two identical circuits will be needed, one for left and one for right.


    Some 2-leaded LEDs produce red and green. These are called Bi-polar LEDs. This circuit alternately flashes a red/green bi-polar LED:

    A 555 is configured as a monostable or one shot in this project. The period of the 555 is determined by the 47k and the capacitor from pin 6 to ground (100n). Time “T” = 1.1 RC  or  1.1 X 50,000 X 0.1 X10 -6  =  0.0055 or 5.5 mS (milli-seconds).
    The 555 receives trigger pulses from the distributor points. These are limited by the 1k and 5v zener diode. These are AC coupled to the trigger input through the 100n coupling capacitor. The 50mA meter receives pulses of current through the 200k pot to show a reading.

    Integration of the current pulses produces a visible indication of the cars engine speed on the 0-1mA meter.
    Supply is taken from the cars 12v system and for the 555 it is reduced to a regulated 9v by the 15 ohm resistor in conjunction with the 9v zener diode. Note: the 10u electrolytic must be placed physically as close as possible to supply pin 8.
  • Hulda Clark’s Zapper Circuit

    This is the circuit for Dr. Hulda Clark’s Zapper, designed in 2003. The frequency is approximately 30kHz positive offset square wave. It has a red LED light that lights up when the unit is on. Perfect for regular zapping, extended zapping and other Hulda Clark related experiments.
    This device is used tocure, treat and prevent any disease. It will cure anything. Simply hold the two probes (one in each hand) for 5-10 minutes then rest for 20 minutes, then repeat two more times. Do this each day and you will be cured. Here is her website: ClarkTestimonials.com Hundreds of people have been cured of everything from herpes to AIDS.
    On the other side of the coin is the claim that Dr Hulda Clark is a complete quack.  Here is a website called: Quackwatch. The second diagram shows the two copper tubes and the circuit in a plastic box. I am still at a loss to see how any energy can transfer from this quack machine, through the skin (50k skin resistance and 9v supply) and zap a bug in your intestine. It’s a bit like saying I will kill all the mice in a haystack by stabbing the stack with a needle.

    This circuit will detect low resistances and high resistances to produce a tone from the speaker.
    It will detect up to 200k and the circuit automatically turns off when the probes are not used.

    When the level of light on the photo-cell decreases, the 555 is activated. Photo-cells (Photo-resistors) have a wide range of specifications. Some cells go down to 100R in full sunlight while others only go down to 1k. Some have a HIGH resistance of between 1M and others are 10M in total darkness. For this circuit, the LOW resistance (the resistance in sunlight) is the critical value.
    More accurately, the value for a particular level of illumination, is the critical factor. The sensitivity pot adjusts the level at which the circuit turns on and allows almost any type of photo-cell to be used.

    Some 3-leaded LEDs produce red and green. This circuit alternately flashes a red/green bi-coloured LED:


    The 555 will activate a relay. When pins 2 and 6 are connected as an input, the chip requires only about 1uA to activate the output. This is equivalent to a gain of about 200,000,000 (200 million) and represents about 4 stages of amplification via transistors.
    In the first circuit, the output will be opposite to the input. The relay can be connected “high” or “low” as show in the second diagram. One point to note: The input must be higher than 2/3V for the output to be low and below 1/3V for the output to be high. This is called HYSTERESIS and prevents any noise on the input creating “relay chatter.”

    An interesting point to remember.
    In the first diagram above, the relay is connected so that it is active when the output is low. This is called NEGATIVE or NEGATIVE LOGIC. It has the same reasoning as-5 – (-5) = 0.
    Or in English:  “I am not NOT going.”
    When the input is low in the first diagram, the output is HIGH and the relay is OFF. The circuitry creates two reversals and makes it easy to see that when the input is LOW, the relay is OFF.

    The 555 is capable of sinking and sourcing up to 200mA, but it gets very hot when doing this on a 12v supply.
    The following circuit shows the maximum number of white LEDs that can be realistically driven from a 555 and we have limited the total current to about 130mA as each LED is designed to pass about 17mA to 22mA maximum. A white LED drops a characteristic 3.2v to 3.6v and this means only 3 LEDs can be placed in series.
  • DUMMY ALARM Circuit

    This Dummy Alarm project makes an LED flash briefly once every 5 seconds to imitate the indicator light of a real alarm.
    The circuit is designed to use very little current to prolong battery life so that it can be left on permanently. An on/off switch is not included, but could be added if you wish. The 7555 timer IC used is a low power version of the standard 555 timer. A �superbright� red LED is used because this provides a bright flash with a low current. The LED is off for most of the time so the average total current for the circuit is less than 0.2mA. With this very low current a set of 3 alkaline AA cells should last for several months, maybe as long as a year.
    Dummy Alarm Circuit
    Parts List
    1x – NE555 Bipolar Timer
    1x – LED (Red)
    1x – 680K Resistor (1/4W)
    1x – 1K Resistor (1/4W)
    1x – 10K Resistor (1/4W)
    1x – 10�F Electrolytic Capacitor (16V)
    1x – 9V Voltage Battery

    Need to flash “turn indicators” using a 555 and a single 20 amp relay. Here is our suggestion. The timing resistor needs to be selected for the appropriate flash-rate.

    Flashing the “TURN INDICATORS”
  • Flashing LED Circuit

    A Circuit that flashes an LED on and off.
    This circuit uses the 555 timer in an Astable operating mode which generates a continuous output via Pin 3 in the form of a square wave. This turns the LED (D1) on and off. The speed at which the LED (D1) is turned on and off is set by the values of R1 and R2.
    Flashing LED Circuit
    Parts List
    1x – NE555 Bipolar Timer
    1x – LED (Red)
    1x – 470K Resistor (1/4W)
    2x – 1K Resistor (1/4W)
    1x – 1�F Electrolytic Capacitor (16V)
    1x – 9V Voltage Battery

    This circuit flashes two red LEDs for a model railway crossing.
  • HEE HAW SIREN Circuit

    Build the circuit and listen. Change the resistors and capacitors to get all sorts of different results.
  • KNIGHT RIDER Circuit

    This circuit mimics the lights in knight rider’s car. They flash one at a time chasing each other.
    In the Knight Rider circuit, the 555 is wired as an oscillator (Astable mode). The output of the 555 is directly connected to the input of a 4017 decade counter.
    The input of the 4017 counter is called the CLOCK line. The 10 outputs Q0 to Q9 become active, one at a time, on the rising edge of the waveform from the 555. Each output can deliver about 20mA but a LED should not be connected to the output without a current-limiting resistor (100R or 220R).
    Using six 3mm LEDs, the display can be placed in the front of a model car to give a very realistic effect. The same outputs can be taken to driver transistors to produce a larger version of the display.
    Knight Rider Circuit
    This circuit consumes 22mA while only delivering 7mA to each LED. The outputs are “fighting“ each other via the 100R resistors (except outputs Q0 and Q5).
    1x NE555 Bipolar Timer
    6x LED (Red)
    8x 100 Resistor (1/4W)
    2x 220 Resistor (1/4W)
    1x 1K Resistor (1/4W)
    1x 68K Resistor (1/4W)
    1x 3.3�F Electrolytic Capacitor (16V)
    1x 4017 Decoded Decade Counter
    1x 9V Voltage battery
  • LASER RAY Circuit

    This circuit produces a weird “Laser Ray” sound and flashes a white LED at approx 5Hz:
  • LATCH Circuit

    This circuit is a LATCH and remains ACTIVE when the push-button has been pressed for an INSTANT and released.
  • LED DICE (with Slow Down) Circuit

    This circuit produces a random number from 1 to 6 on LEDs that are similar to the pips on the side of a dice. When the two TOUCH WIRES are touched with a finger, the LEDs flash very quickly and when the finger is removed, they gradually slow down and come to a stop.

  • LED DIMMER Circuit

    This circuit will adjust the brightness of one or more LEDs from 5% to 95%.

    This circuit detects light falling on the Photo-cell (Light Dependent Resistor) to turn on the 555 and create a tone that is delivered to the speaker. Pin 4 must be held below 0.7v to turn the 555 off. Any voltage above 0.7v will activate the circuit. The adjustable sensitivity control is needed to set the level at which the circuit is activated.  When the sensitivity pot is turned so that it has the lowest resistance (as shown in red), a large amount of light must be detected by the LDR for its resistance to be low. This produces a voltage-divider made up of the LDR and 4k7 resistor. As the resistance of the LDR decreases, the voltage across the 4k7 increases and the circuit is activated.
    When the sensitivity control is taken to the 0v rail, its resistance increases and this effectively adds resistance to the 4k7. The lower-part of the voltage-divider now has a larger resistance and this is in series with the LDR. Less light is needed on the LDR for it to raise the voltage on pin 4 to turn the 555 on.

  • MACHINE GUN Circuit

    This circuit produces a sound very similar to a machine gun:
  • Metal Detector Circuit

    A circuit that detects metal and also magnets.
    When a magnet is brought close to the 10mH choke, the output frequency changes.
    Metal Detector Circuit
    Parts List
    1x – NE555 Bipolar Timer
    1x – 47K Resistor (1/4W)
    2x – 2.2�F Electrolytic Capacitor (16V)
    1x – 10�F Electrolytic Capacitor (16V)
    1x – 10�F Electrolytic Capacitor (16V)
    1x – 10mH Inductor
    1x – 8 Ohm Speaker (1/4W)
    1x – 9V Voltage Battery
  • Metronome Circuit

    A Metronome is a device used in the music industry to indicate the rhythm by a ‘toc-toc’ sound.
    This circuit uses the 555 timer in an Astable operating mode and generates a continuous output via Pin 3 in the form of a square wave. This is then passed through the 22�F electrolytic capacitor to create a smooth oscillation which then creates the ‘toc-toc’ sound. The speed of the output is controlled by the 250K Potentiometer (VR1).
    Metronome Circuit
    Parts List
    1x – NE555 Bipolar Timer
    1x – 1K Resistor (1/4W) 2x – 22�F Electrolytic Capacitor (16V)
    1x – 250K Potentiometer
    1x – Loudspeaker (8 Ohm)
    1x – 9V Voltage Battery

    Here is a circuit that will convert any clock mechanism into Model Railway Time.
    For those who enjoy model railways, the ultimate is to have a fast clock to match the scale of the layout. This circuit will appear to “make time fly” by turning the seconds hand once every 6 seconds. The timing can be adjusted by changing the 47k. The electronics in the clock is disconnected from the coil and the circuit drives the coil directly. The circuit takes a lot more current than the original clock (1,000 times more) but this is one way to do the job without a sophisticated chip.


    This circuit produces a tone above the human audible range and this is supposed to keep the mosquitoes away. You need a piezo diaphragm that will respond to 15kHz and these are very difficult to find.
  • MOTOR PWM Circuit

    The speed of a motor can be adjusted by this circuit, from 5% to 95%.
  • MUSIC BOX Circuit

    This circuit produces 10 different tones and by selecting suitable values to change the voltage on pin 5, the result can be quite pleasing. Note: the two unused outputs of the 4017 produce a tone equal to that produced by the 555 when pin 5 has no external control voltage.


    This circuit flashes the left LEDs 3 times then the right LEDs 3 times, then repeats.
    This circuit uses a 555 timer which is setup to both runn in an Astable operating mode. This generates a continuous output via Pin 3 in the form of a square wave. When the timer’s output changes to a high state this triggers the a cycle on the 4017 4017 decade counter telling it to output the next sequential output high. The outputs of the 4017 are connected to the LEDs turning them on and off.
    Police Lights Circuit

    Parts List
    1x – NE555 Bipolar Timer
    1x – 4017 Decoded Decade
    6x – 1N4148 Diode
    1x – 1K Resistor (1/4W)
    1x – 22K Resistor (1/4W)
    2x – 4.7K Resistor (1/4W)
    6x – 470 Resistor (1/4W)
    1x – 2.2�F Electrolytic Capacitor (16V)
    2x – BC547 NPN Transistor
    2x – LED (Blue)
    2x – LED (Red)
    1x – 9V Voltage Battery
  • POLICE SIREN Circuit

    The Police Siren circuit uses two 555′s to produce an up-down wailing sound. The first 555 is wired as a low-frequency oscillator to control the VOLTAGE CONTROL pin 5 of the second 555. The voltage shift on pin 5 causes the frequency of the second oscillator to rise and fall.
  • RAIN ALARM Circuit

    This circuit consumes no current until moisture is detected on the rain plate.

    This is a game for two players.
    Player 1 presses the START button. This resets the 4026 counter chip and starts the 555 oscillator.
    The 555 produces 10 pulses per second and these are counted by the 4026 chip and displayed on the 7-Segment display.
    The second player is required to press the STOP button. This freezes the display by activating the Clock Inhibit line of the 4026 (pin 2).
    Two time-delay circuits are included. The first activates the 555 by charging a 10u electrolytic and at the same time delivering a (high) pulse to the 4026 chip to reset it. The second timer freezes the count on the display (by raising the voltage on pin 2) so it can be read.
  • ROULETTE Circuit

    This circuit creates a rotating LED that starts very fast when a finger touches the TOUCH WIRES. When the finger is removed, the rotation slows down and finally stops.
  • SCREAMER Circuit

    This circuit will produce an ear-piercing scream, depending on the amount of light being detected by the Light Dependent Resistor.
  • SERVO TESTER Circuit

    This circuit can be used to manually turn a servo clockwise and anti-clockwise.  By pushing the forward or reverse button for a short period of time you can control the rotation of the servo. It will also test a servo.
    Here is a photo of a kit from Cana Kit for  $10.00 plus postage (it is a slightly different circuit) and a motor and gearbox, commonly called a “servo.” The output shaft has a disk or wheel containing holes. A linkage or push-rod is fitted to a hole and when the disk rotates, the shaft is pushed and pulled. The shaft only rotates about 180� to actuate flaps or ailerons etc.

    A pot can be used to control the position of the servo by using the following circuit. It produces a positive pulse between about 0.9 milliseconds and 2.1 milliseconds. The off period between pulses is about 40 milliseconds. This can be shortened by reducing the value of the 3M3 resistor.