Switch-Off Delay - Maker Factory ELECTRONICS EXPERIMENTS BOX Manual

at night. During charging, that is, when the sun is shining, the transistor turns the LED off. The transistor
switches the red LED on as soon as it is getting dark.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.25.

2.10 Switch-off delay

Circuit 26: 2 seconds switch-off delay
Setup information
Install the two transistors and the two diodes as shown in Fig. 2.26. Then install the four resistors and the
electrolytic capacitor. The seven jumpers come next.
The jumper acting as the switch (shown dashed) is installed last. Only one end of the jumper wire is con-
nected, the other is open. Check the placement on the board again and only then connect the battery.
Experiment
Even if everything is wired correctly, nothing will happen at first; the red LED remains dark. But if you close
the switch, that is, you insert the jumper wire for a moment, the LED will go on. But when you open the
switch, the LED will not turn off immediately but will glow for more 2 seconds. The delay time is primarily
defined by the value of the electrolytic capacitor C1 and the value of the resistor R3. Try out other component
values and check the delay time that this will produce.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.26.
Components required:
2 x 2N3904 transistors,
1 x red LED, 1 x 1N4148
silicon diode,
2 x 1 kΩ resistors,
2 x 100 kΩ resis-
tors, 1 x 10 μF elec-
trolytic capacitor ,
1 x breadboard, 1 x 9V
battery with clip con-
nector
Fig. 2.26: 2 seconds switch-
off delay
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