Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 154

Circuit 131: 15 seconds switch-off delay
Setup information
Install the two transistors, the diode, the three resistors and the electrolytic capacitor as shown in Fig. 2.131
The six jumper wires come next followed by the jumper, which serves as a switch (shown dashed). For your
guidance, we labelled the "switch" with Start. Check the placement on the board again and only then con-
nect the battery.
Experiment
Even if everything is wired correctly, nothing will happen at first. But when you activate, which means clos-
ing the Start switch, the red LED will go on after a short delay. The delay time in our case is about 15 sec-
onds. When the "switch" is opened again, the red LED turns off. This basically is equivalent to the switch off
delay. The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.131.
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Components required:
2 x 2N3904 transistors,
1 x BAT85 Schottky
diode, 1 x red LED,
1 x 1 kΩ resistor,
1 x 220 kΩ resistor,
1 x 1 MΩ resistor,
1 x 100 μF elec-
trolytic capacitor,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.131: 15 seconds switch-
off delay