Elenco Electronics 202 - Manual (Page 120)

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Project #282
OBJECTIVE: To build a circuit that turns off an LED for 4 seconds.
Turn Off Timer
OBJECTIVE: To build a circuit that turns off the bulb and turns
on the LED for 4 seconds.
Modify the circuit from project #283 by placing a 1-snap on top of the
NPN transistor (Q2) at base grid location E6 (on level 3). Then place
the red LED (D1) over it, across base grid locations E4-E6 (on level 4),
(+) is on E6. When you press the press switch (S2), the lamp (L2)
turns off and the LED lights. When the voltage from the discharging
capacitor drops low enough, Q1, Q2, and the lamp turn on and the
LED turns off.
Project #283
Turn Off Timer (II)
Turn on the slide switch (S1). Pressing the press switch (S2) down
increases the voltage at the base of Q1. This turns the Q1, Q2, and
LED (D1) off as the capacitor (C4) charges up. As you release the
press switch, the capacitor starts discharging through resistor R5.
When the voltage from the discharging capacitor drops low enough,
Q1,Q2, and the LED turns off for about 4 seconds. Now change the
100
μF capacitor (C4) to 470μF (C5) and the LED should stay off for
about 10 seconds.
Replace the LED (D1) and 100 Ω resistor with a 3-wire snap and 6V lamp (L2).
OBJECTIVE: To modify project #282 to use the 6V bulb.
Project #284 LED & Bulb Timer