Dark sensor using 2 transistor BC547
When light falls on LDR, its low resistance drives the transistor T1 into conduction. This keeps transistor T2 cut-off due to low base bias. The LED does not get power as long as ambient light falls on it.
Parts list
- T1 and T2 – BC 547
- LDR -1 nos
- Resistance R1 – 1k
- R2 & R3 – 330 Ohms
- 6 volt battery
Modifying the above circuit to use with Relay and switch on / off
You can also modify the above circuit in controlling AC appliances. Remove R2 and LED from the circuit and also remove the positive connection to Pole of the relay. Connect the AC bulb or any other appliance as shown
With slight modification this can be used with 9v battery.
why when its light is open the LED will light and when the Light is off the LED also will off its not a dark sensor its light sensor?
Title might look opposite to what it is actually doing but the message that I need to convey should be clear.
Could you please give an explanation for selecting resistor values
Which resistor ? If you are talking about R3 then its dependent on source voltage that you intend to use.