Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 226

Circuit 203: 7 seconds switch-off delay
Setup information
Install the transistor, the diode, the four resistors and the electrolytic capacitor as shown in Fig. 2.203 fol-
lowed by the three jumper wires and the jumper, which serve as switch (shown dashed). For your guidance,
we labelled the "switch" with Start. 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. But when you activate the Start switch,
that is, when you insert the wire, the red LED will go on after a short delay. When the "switch" is opened
again, the red LED will continue to glow for a certain time. In our case this delay is about 7 seconds. If you
use different values for R1 and C1, you can also accomplish longer delay times. Use it for example, to set up
a stair lighting solution.
The circuit diagram for this experiment is shown in Chap. 3, Fig. 3.203.
228
Components required:
1 x 2N3904 transistor,
1 x red LED, 2 x 1 kΩ resis-
tors, 1 x 10 kΩ resistor,
1 x 100 kΩ resistor,
1 x 100 μF electrolytic
capacitor, 1 x breadboard,
1 x 9V battery with clip
connector
Fig. 2.203: 7 seconds switch-off
delay