Light Operated Relay

Light operated Relay circuit

An easy to build light operated relay circuit is given here. The circuit uses versatile Cmos IC 4011 for stability of operation and wide operating voltage.  Normally the relay is open when light is present. When light falling on the LDR is interrupted the relay gets energised and closed. Thus the activation of the relay triggers anything that is connected to the relay. 

Parts list:

U1 – IC 4011

Q1 – BC149

R1 – 10M ohms – Resistor

R2 – 10K ohms – Resistor

R3 – LDR ( Light Dependant Resistor)

R4 – 100K Preset 

R5 – 2.2M ohms – Resistor 

C1 – 100 MFD/16V electrolytic capacitor

D1 – IN4148 Diode

K1 – SPDT Relay

Circuit description

Very compact 

Versatile

Inexpensive

Easy to build using single IC 4011

When light falling on LDR is interrupted relay will be activated

Can be used as counters 

If you want to assemble this light operated relay , it can be done with the ready made PCB shown here. 

The copper design should be etched on the copper clad board and the PCB is easily fabricated. 

Assembling is pretty easier with the board.