Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 103

Circuit 80: Quiztimer 30 seconds
Setup information
Install the two transistors, the diode and the four resistors as shown in Fig. 2.80. The seven jumper wires
come next. Finally, insert the six jumper wires, which will function as a switch (shown dashed). Check the
placement on the board again and only then connect the battery.
Experiment
This is a classic circuit with switch-off delay. If everything is wired correctly, the "switch" is On, meaning
that one end of the jumper is not connected. Connect the jumper momentarily. The red LED turns on. When
you open the switch, the quiz clock starts running; in our case this is 30 seconds Naturally, difficult ques-
tions or complex games require more time. The answer must be given or the next move must have followed
during the time the red LED is lit.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.80.
Components required:
2 x 2N3904 transistors,
1 x red LED, 1 x 10 Ω resis-
tor, 2 x 1 kΩ resistors,
1 x 220 kΩ resistor,
1 x 100 μF electrolytic
capacitor, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.80: Quiztimer 30 seconds
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