User manual

Mission: Put the circuit for several minutes in the cold outdoors and examine the
influence of lower temperatures. Put the circuit directly onto the heater and look for
the warmest place in the room: 4 points.
16 As a Geiger counter…
Behind the 16th door, you will find a next disk capacitor of only 10 nF (label 103) this time. Integrate it into the tone generator. Modified resistors are also used to
adjust the tone. Besides, the resistor integrated previously into a negative feedback loop is replaced by a red LED, which will now act as a light sensor. The
resulting model is a tone generator, whose frequency depends on brightness. In the dark, you will hear only crackles. Once the sensor is exposed to light, the
frequency of the tone rises. With a little imagination, it can be perceived as a Geiger counter, close to which a radioactive sample is brought.
Info: the LED has two functions in this experiment. In the forward-biased direc-
tion, it behaves as any other diode and enables rapid discharge of the capacitor.
In contrast, in the reverse-biased direction, it insulates and only allows the
current, which depends on the brightness. Therefore, the circuit produces short
impulses with a frequency that increases with brightness.
Mission: integrate an additional 100 nF capacitor to reduce the frequency even
more. In the dark, only single crackles should be heard and weak flashes of the
red LED should be seen. Check which LED has the lowest reverse current and
thus produces the lowest frequency in the dark. Now, the noise resembles a
Geiger counter even more and you get: 4 points.
17 Electronic organ
Behind the door number 17, there is a 100 k

resistor (brown, black, yellow). Convert the tone generator into an electronic organ. Normal instruments have many
keys, while this one has only two contacts that function as touch sensors. If both contacts are touched by the fingers, a resistance is formed, which defines the
tone. A firmer pressure produces a higher pitch.
Info: the circuit resembles the Geiger counting oscillator from the
previous day, however, with the 100 k

resistor in the control feed-
back loop, it has an adjusted frequency range. Besides, there is a
buffer amplifier with simple voltage amplification serving for proper
separation of the sound generator. Thereby, the feedback effects on
the oscillator are avoided, which might occur in the self-resonance
area of the converter.
Mission: exercise with this instrument and play a Christmas carol. If
others are able to recognize the carol, you get: 5 points.