THE PULSER AND ASTABLE MODULE

This is a unit designed to produce pulses; it has five different output frequencies
(i) a pulse when you press a switch (the pulser input)
(ii) a 1Hz output (1 pulse per second)
(iii) a 10Hz output (10 pulses per second)
(iv) a 100Hz output (100 pulses per second)
(v) a 1000Hz (1 kHz) output (1000 pulses per second)


The outputs of these are what we call SQUARE WAVES examples are shown in the diagram.

Notice how long one complete pulse is.

THE CLOCKED BISTABLE UNIT

You will probably have looked at the bistable unit which has two inputs and two outputs. Remember that the output can only be changed by pressing the other input.

The CLOCKED BISTABLE still has these two inputs (S and R but the output can also be changed by the CLOCK INPUT from the pulser/astable unit.

The output of the CLOCKED BISTABLE is changed when the clock pulse FALLS TO ZERO. We call this the FALLING EDGE of the pulse. You can see this in the diagram.

This means that if we apply a pulse to the clock input nothing happens, it is only when we remove the pulse that the output changes.

You should see that this means that the output will change half as often as the input and therefore will have half the frequency of the input.

This property is particularly useful in counting circuits you can see in the file called Counting circuits.

THE DRIVER RELAY MODULE

You will find that the output from the NAND gate is not sufficient to run a motor, it may not even be enough to operate a buzzer if the batteries are at all flat.
(NAND gate output current is a few milliamps while the motor requires many hundreds of milliamps to run it)
You can overcome this problem with the DRIVER RELAY module. This allows a small current to operate a switch that will allow a much larger current to flow in another circuit.

The applications of the driver relay module include:
(a) reversing an electric motor
(b) reversing an electrc motor with a bistable
(c) an automatic light (suggest a 12V 0.1A MES bulb here)