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Monday, January 14, 2008

Two-LED Pilot Light

230 or 115 Vac mains operated -- Very simple circuitry

Circuit diagram:

R1,R2__________27K 1W Resistors (See Notes)
R3______________6K8 1/4W Resistor

D1,D2_______1N4007 1000V 1A Diodes
D3_____________Green LED
D4_______________Red LED

Q1_____________BC337 45V 800mA NPN Transistor
SW1____________SPST Mains switch (See Notes)


This circuit was designed on request and can be useful to those whishing to have, say, a red LED illuminated when an appliance is on and a green LED illuminated when the same appliance is off.
Any mains operated appliance can be monitored by this circuit, provided a suitable mains switch, capable of withstanding the full load current, is used for SW1.
When SW1 is closed, the load and D4 are energized, Q1 is saturated and shorts D3, thus preventing its illumination.

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