Elenco Circuit Maker Sound Plus 200 - Manual (Page 48)

Project #101
Light-Controlled SCR
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Project #98
Turn on the slide switch (S1) and the
LED (D1) comes on if there is light on
the photoresistor (RP). If you cover the
photoresistor, then the LED will stay on
for a while, until the 100mF capacitor
(C4) discharges.
Slow Light
Dimmer
In the preceding circuit, speed up how quickly the
LED shuts off by replacing the 100mF capacitor
(C4) with the smaller 10mF capacitor (C3).
The 0.1mF capacitor (C2) stores very little
electricity, so if you replace the 10mF capacitor with
it then the LED will shut off right away.
Project #100
The transistors (Q1 & Q2) are connected so when the base of Q2 goes high, both
Q2 and Q1 turn on. They will remain on until the slide switch (S1) is turned off.
Turn on the slide switch and the LED (D1) should not light. Now press the press
switch (S2) and the LED lights. Turn the LED off by turning the slide switch off.
The two transistors act as an electronic device called an SCR (Silicon
Controlled Rectifier). A three-pin device that once its base is triggered, remains
on until the current flow through it stops.
The SCR
Replace resistor R3 with the photoresistor (RP). The LED (D1) will only light
when the press switch (S2) is pressed and there is enough light on the
photoresistor. Turn on the slide switch (S1) and place your finger over the
photoresistor. Press the press switch and the LED should not light. Remove your
finger and press the press switch again, the LED should light now.
Project #99
Not-So-Slow
Light
CM-200_Manual_031914.qxp_CM-200_Manual_031914 4/2/14 12:04 PM Page 48