User manual
second LED is thus free for the actual test and shows the distributed frequency. Between the oscillator
and Q4, there are four divider steps that divide the frequency of the clock signal respectively by two.
Thus, 16 clock pulses add up to one output impulse. The elementary period is four seconds at the
oscillator and about one minute at the output Q4.
12 Counter from zero to three
Behind the twelfth door is another 10kΩ resistor (brown, black, orange), which is placed in the
oscillator. The frequency is indeed increased again to around 50Hz, but this time an LED is placed at
the output Q5, which divides the clock signal by 32. At the two LEDs, one therefore sees one faster and
one slower flashing. Both signals together can be read as a 2-bit binary number.
The counter thus constantly counts from zero to three. Then it runs over and continues with zero.
Observed more closely, the LEDs display multiples of 8, that is, 0, 8, 16, and 24 input pulses of the
oscillator. The first three divider steps act as pre-scaler by 8 and deliver a clock signal of around 6 Hz,
which can still be easily followed with the eye. If you would like to see the counter more slowly, you
can insert the 22-MΩ resistor in the circuit. The counter state then switches roughly in the period of
half-minutes, so that one has built a simple digital clock.
13 Three-bit counter to seven
Behind Door Number 13 you will find a yellow LED. With this addition, the counter should be expanded
to three bits. There are now a total of eight different counter states between 000 (zero) and 111 (seven).
The two red LEDs at the outputs Q5 and Q6 share a joint series resistor. The flashing with the lowest
frequency occurs at Q6.
A resistance for two LEDs is possible but leads to a special effect. The red LED at Q6 displays two
brightness levels. As long as Q5 and Q6 are switched on, the current distributes itself through the series
resistor to two LEDs. In the first tests, relatively high LED series resistors of 10 kΩ were deliberately
used. One thereby achieves only an adequate brightness and can experiment without being blinded.
Plus, this circuitry saves energy so that the battery will last as long as possible to the end of the testing.
14 Three-four time
Behind the 14th door you will find another 10 kΩ resistor (brown, black, orange). It is now installed