Light activated relay circuit using BC547 & BC337

This light activated relay circuit is simple form but can be useful various such as The alarm circuit, an more electronic control circuits such as ON-OFF electrical equipment, the flash light control circuit or etc. following with do you want.

Function of light activated relay circuit
From the circuit in Figure 1 that see two transistor Q1 BC547,Q2 BC337 join together in Darlington compound In order to have a higher increase rates.

When has a light on the photocell (LDR1) The resistance will reduce. The bias voltage is supplied to the transistor up, just enough to make transistors and relays it to work.

The VR1 is a base circuit of the transistor that controls the sensitivity of the circuit.
If the offer is less so. The sensitivity of the circuit is low, It provides very valuable. The high sensitivity.

To operate the device in the PCB properly. In Figure 1 soldered properly. Try entering a power source in the circuit. then adjusted the VR1 to sensitivity by do you want.

The Circuit diagram of Light Relay Switch By BC547 and BC337

pcb-layouts-of-dayLight-sensor-switch Relay Switch By BC547 & BC337
PCB layouts and Components layout of the Light Relay Switch By BC547 and BC337

You can buy parts in this projects below.

DC 9V 9 V 5PIN 250VAC 28VDC Mini Power Relay SPDT

100PCS 1A 1000V Diode 1N4007

50 Pieces TRANSISTOR BC547C NPN 45V 100mA TO-92



  1. Sachin Shetty March 14, 2014
  2. Madhu April 4, 2016

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