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Circuit 31 – Dry sensor (Transistor).
Member rating: No Rating | Words: | Submitted: Fri Oct 17 2003
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Circuit 31 - Dry sensor (Transistor). Function This circuit could be used to detect if soil is too dry. Circuit diagram Components SW1 = Toggle Switch VR1 = 1M ohm R1 = 470 ohm R2 = 2200 ohm R3 =1k ohm Transistor = BC108 5mm Standard LED Operation This circuit uses a transistor (BC108) as an electronic switch. Transistor action. When the voltage on the base of the transistor is less than 0.6V the transistor is switched off. No current can flow through the transistor from the collector to the emitter, so no current can flow through R1 and the LED. Thus the LED is unlit. If more than 0.6V is applied to the base, the transistor switches on. Now current can pass easily from the collector to the emitter, so current can flow from the top rail, through R1, the LED and the transistor, back to the battery. The LED is now lit. Resistance of the probes Resistance of the probes will be referred to as RP....
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