Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 102

Circuit 79: Quiztimer 8 seconds
Setup information
Install the two transistors, the diode and the four resistors and the two electrolytic capacitors as shown in
Fig. 2.79. The nine jumper wires come next. Finally, insert the jumper wire, 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 8 seconds. During this time, the ques-
tion must be answered or the next move must be performed.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.79.
104
Components required:
2 x N3904 transistors,
1 x red LED, 1 x 10 Ω resis-
tor, 2 x 1 kΩ resistors,
1 x 220 kΩ resistor,
2 x 10 μF electro-
lytic capacitors,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.79: Quiztimer 8 seconds