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Back to top. All the circuits in this eBook require DC. Only 1 button can be pressed at a time, that's why it is called a monophonic organ. You can change the 1k resistors to produce a more-accurate scale.

When a magnet is brought close to the 10mH choke, the output frequency changes. Changing the voltage on pin, 5 via the diode, adjusts the timing of the chip. The output will deliver about 50mA. Pin 3 goes LOW to about 0. When pin 3 goes LOW, capacitor "a" charges via diode "a" to about 11v. When pin 3 goes HIGH, capacitor "a" has about 11v across it, plus the voltage on pin 3.

This produces a voltage of 21v on the anode of diode "c. It operates very similar to pulse-width modulation. The component values cause the 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.

Pin 4 must be held below 0. Any voltage above 0. 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 on. Photo-cells Photo-resistors have a wide range of specifications.

Some cells go down to R in full sunlight while others only go down to 1k. 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. When pin 3 is LOW, the n discharges through the k to 0v.

Pressing the switch upsets the 3v created by the two 10k voltage dividers, triggering the flip flop inside the and changing the state of the output from HIGH to LOW or vice-versa. The output of the drives a transistor to turn a globe on and off. The second circuit is a Memory cell and is the basis of the memory in a computer.

It works like this: When the circuit is turned on, pin 6 does not see a high and pin 2 does not see a low, so the starts in reset mode. The period of the is determined by the 47k and the capacitor from pin 6 to ground X10 -6 n. The receives trigger pulses from the distributor points.

These are AC coupled to the trigger input through the n coupling capacitor. The 50mA meter receives pulses of current through the k pot to show a reading. Integration of the current pulses produces a visible indication of the cars engine speed on the mA meter. Supply is taken from the cars 12v system and for the 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.

Connect the circuit to the output of an amplifier. It is best to detect one frequency at a time. Integration of the audio frequency produces a visible indication on the mA meter. 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. A linkage or push-rod is fitted to a hole and when the disk rotates, the shaft is pushed and pulled. 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. The off period between pulses is about 40 milliseconds. This can be shortened by reducing the value of the 3M3 resistor.

The circuit diagram shows the toggle switch is clicked towards the lid of the box and this starts the servo motor. The servo has an arm that comes out of the box and clicks the switch to the opposite position.

This reverses the servo and the arm retreats into the box and hits the limit switch that turns the circuit off.

You may have to adjust the value of the 15k and 27k resistors and you will also see other videos on the Instructables website to help you with construction. As the website says: "It's the most useless invention, but everyone wants one. Output pin 3 drives the circuit with a positive then zero voltage.

The other end of the circuit is connected to a voltage divider with the mid-point at approx 4. This allows the red and green LEDs to alternately flash when no transistor is connected to the tester.

If a good transistor is connected, it will produce a short across the LED pair when the voltage is in one direction and only one LED will flash. The answer is to use a buffer transistor. For mA, use a BC or equivalent. But when the chip is sinking mA, pin 3 has about 1. This means the chip does not provide full rail voltage to the load.

This can be improved by connecting pin 7 to pin 3. Pin 7 has a transistor that connects it to 0v rail at the same time when pin 3 is LOW. They can both be connected together to improve sinking capability. In this case the low will be mV for mA instead of mV, an improvement of mV. This will add 1v1 to the load and also make the chip run cooler. You can add a dropper resistor current limiting resistor but the current will reduce as the supply voltage drops. To provide a constant output current to a device such as an IR LED, the following circuit can be used.

The current will be constant for any supply voltage but the best range will be 7v to 12v. The current is determined according to the value of R. The solution is to add a push-pull output. The following arrangement has been chosen as it swings almost rail-to-rail but two faults need to be addressed.

Both transistors turn on during the brief interval when pin 3 is travelling from high to low or low to high. This means the two transistors will put a "short" across the power rail. The addition of the 4R4 will allow a high current to flow but the transistors will not be damaged. In addition, green LEDs on the base of each transistor reduces the time when both transistors are ON. The animation shows how the transistors are turned on and off and deliver a high current to the load.

The animation shows how NPN and PNP transistors follow an input signal in a push -pull arrangement using positive and negative supply rails. This is not the same as our circuit however the basic effect applies. The output is inverse of pin3 but pin3 only needs to deliver milliamp and the transistors can deliver 1 amp or more to the load. This allows the to be kept cool. These are called Bi-polar LEDs. See Talking Electronics website, left index, Transistor Circuits circuits and go to Zener Diode making to see how to make a zener diode and how to create a zener voltage from a combination of zeners.

Place the zener across the terminals in the circuit below and read the value across it with a multimeter set to 50v range. Releasing the button decreases the wailing. The circuit automatically turns off after about 30 seconds. It will detect up to k and the circuit automatically turns off when the probes are not used.

The wattage will depend on the driver transistors and transformer. It is a switch-mode boost circuit.

When the normally-closed push button is pressed, it opens and the uncharged 1u will be pulled to nearly 0v rail via the 10k and this will take pin 2 LOW to make output pin 3 HIGH for the duration determined by the 22u and k. If the push-switch stays open, the 1u will charge via the k and eventually the output of the will go low. But normally the switch must be pressed for a short period of time so that the timing components k and 22u make the output go HIGH for a short period of time.

The action cannot be repeated until the 10u charges or discharges via the k. It can be adjusted to give the desired speed for the display. The output of the is directly connected to the input of a Johnson Counter CD The 10 outputs Q0 to Q9 become active, one at a time, on the rising edge of the waveform from the Each output can deliver about 20mA but a LED should not be connected to the output without a current-limiting resistor R in the circuit above. The first 6 outputs of the chip are connected directly to the 6 LEDs and these "move" across the display.

The next 4 outputs move the effect in the opposite direction and the cycle repeats. The animation above shows how the effect appears on the display. 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. The outputs are "fighting" each other via the R resistors except outputs Q0 and Q5. He needed to flash "turn indicators" using a and a single 20 amp relay.

Here is our suggestion. The timing resistor needs to be selected for the appropriate flash-rate. In the first circuit, pin 2 must see a LOW for the circuit to activate. If sufficient static voltage is detected by the plate, the chip will change state. If not, you will need to touch the plate and the 0v rail. In the second circuit, two touch plates are provided and the resistance of your finger changes the voltage on pin 2 or 6 to toggle the The circuit can be made times more sensitive by adding a transistor to the front-end as shown in the diagram below: to Index SIREN dB This is a very loud siren and if two or more piezo's are located in a room, the burglar does not know where the sound is coming from.

A robber will not stay anywhere with an ear-piercing sound as he cannot hear if someone is approaching. It's the best deterrent you can get. The "F" contact on the piezo is "feedback" and is not needed in this circuit.

The voltage shift on pin 5 causes the frequency of the second oscillator to rise and fall. Change the resistors and capacitors to get all sorts of different results. This is one. A solar tracker should consume little or no current when waiting for a the sun to change position. That's why we have not designed a circuit.

Hulda Clark's Zapper, designed in 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 to cure, treat and prevent any disease. It will cure anything. Simply hold the two probes one in each hand for minutes then rest for 20 minutes, then repeat two more times. Do this each day and you will be cured. Here is the. 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.

See Latch circuit and Memory Cell above. You need a piezo diaphragm that will respond to 15kHz and these are very difficult to find. 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 ,, 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. In the first diagram above, the relay is connected so that it is active when the output is low. It is the same circuit with a different name. We have also animated the circuit to show how the output goes high or low according to the input level.

It prevents false triggering because as the input rises, the output does not change until the input voltage is fairly high. This means small fluctuations noise on the input do not have any effect on the output.

The second diagram shows a Schmitt Trigger building block. Note: the two unused outputs of the produce a tone equal to that produced by the when pin 5 has no external control voltage. This resets the counter chip and starts the oscillator. The produces 10 pulses per second and these are counted by the 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 pin 2. Two time-delay circuits are included. The first activates the by charging a 10u electrolytic and at the same time delivering a high pulse to the 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. The animation shows the lighting sequence and this follows the Australian-standard. The red LED has an equal on-off period and when it is off, the first delivers power to the second A supply voltage of 9v to 12v is needed because the second receives a supply of about 2v less than rail.

This circuit also shows how to connect LEDs high and low to a and also turn off the by controlling the supply to pin 8. Connecting the LEDs high and low to pin 3 will not work and since pin 7 is in phase with pin 3, it can be used to advantage in this design. But the second is not turned on all the time! The first turns on and the u is not charged. However the output feeds the second and it turns on. The second u starts to discharge, but the first u is charging via a k and after the orange LED has been on for a short period of time, the first changes state and pin 3 goes LOW.

This turns on the red LED and turns off the second The first u starts to discharge via the k and eventually it changes state to start the cycle again. The secret of the timing is the long cycle-time of the first due to the k and the short cycle due to the 47k on the second The seemingly complex wiring to illuminate the lights is shown to be very simple.

The following circuit shows the maximum number of white LEDs that can be realistically driven from a and we have limited the total current to about mA as each LED is designed to pass about 17mA to 22mA maximum.

A white LED drops a characteristic 3. It produces a constant signal that interferes with the signal from a remote control and prevents the TV detecting a channel-change or any other command.

This allows you to watch your own program without anyone changing the channel!! The circuit is adjusted to produce a 38kHz signal. A Photo diode is a receiving diode. There are so many IR emitters that we cannot put a generic number on the circuit to represent the type of diode.

The current through the IR LED is limited to mA by the inclusion of the two 1N diodes, as these form a constant-current arrangement when combined with the transistor and 5R6 resistor. The 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 produces different patterns before the sequence repeats and you have to build the project to see the effects it produces on the 3D cube.

The first circuit charges a u and the transistor amplifies the current entering the u and delivers times this value to the LED via the collector-emitter pins. The second circuit requires a very high value electrolytic to produce the same effect. In this design the current can be 3 amps or more, depending on the supply voltage, the resistance of the load and the type of driver transistors. About 2v5 is lost between "c and e" due to the output of the and the base-emitter voltage of the driver transistors.

This circuit drives an ultrasonic transducer speaker at 20kHz to 40kHz to subdue dog barking. If the unit is turned on by remote control every time the dog barks, the animal will soon learn to cease barking. The maximum frequency response will be about 30kHz. Two identical circuits will be needed, one for left and one for right. The following circuits reduce the voltage to 12v: 30mA: If the circuit takes less than 30mA the takes 10mA you can use a mW zener diode to drop the 24v supply to 12v for the In other words, 12v is dropped across the zener.

Up to mA: The next circuit will allow up to mA. The transistor will need to be placed on a large heatsink. It is an emitter-follower-regulator transistor and can be used with a mW zener. The output voltage is 0. Up to mA with "Amplifier Zener" A mW zener can be converted to a "Power Zener" by combining with a transistor as shown in the following circuit: In other words, if the top rail is 24v, the bottom rail will be Up to 1A: Using the next circuit will allow the to take mA and the load to take mA.

The will need to be placed on a large heatsink. The only difference is the choice of chips. The kit includes the parts and PC board. When the finger is removed, the rotation slows down and finally stops. 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, times more but this is one way to do the job without a sophisticated chip.

The creates a delay of 1 minute and the train moves to the home limit and stops. Turn the power on-off to restart the action. 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. 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. The network of C3 and R4 form a low current holding circuit for the relay.

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.

The direction of rotation is determined by the double-pole double-throw switch. The stepper motor used in this circuit came from an old scanner. It had 5 wires: red-black-yellow-brown-orange. The LEDs illuminate via the back-emf of the coils and prevent the spikes entering the transistors.

The LEDs will flicker to show the pulses being received by the stepper motor. The 27k stop-resistor limits the upper-frequency of the and prevents the circuit producing pulses that are too fast for the stepper motor. The animations are selected by the position of a k pot and when the animation is showing, the pot can be adjusted to increase the speed of the animation. Click the link above and you will be sent an email with the costs. This is an ideal project you get you into surface-mount technology and you can add it to a model layout or build it into a Lego brick for a junior member.

The chip can be used as a complete alarm system. All you need is a piezo diaphragm and the output will be enough for a single room. To create a very loud output you can add a buffer transistor and piezo speaker and the sounds will be deafening. Just think of it.

All the components are available from Talking Electronics and you just need to email Colin Mitchell: talking tpg. The output is set to produce an alarm for 3 minutes then stops.

Pin 2 is LOW when the chip is at rest. To get a very loud output, pin 2 drives a Darlington transistor and piezo tweeter with a 10mH choke across the piezo to produce a waveform of nearly v.