An LDR (Light Dependent Resistor) and preset let you choose the light level at which the relay energizes and de-energizes.
COMMENTS Homer SUGGESTIONS

Two Light Operated Relays - Support Material

MORE CMOS CIRCUITS

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Circuit No.1 - Description

Click Here For A Photograph Of The Prototype.

Circuit Diagram For 
A Light Controlled Relay
Learn More About Cmos Inverters


Circuit No.1 - Parts List

Parts List

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UK & Ireland
Maplin



Circuit No.2 - Description

Click Here For A Photograph Of The Prototype.

Circuit Diagram For 
A Light Controlled Relay
Learn More About Cmos Inverters


Circuit No.2 - Parts List

Parts List

Suppliers





Worldwide
RS Components





UK & Ireland
Maplin



Construction Guide

Click here if you're new to constructing stripboard projects.

The prototypes of both circuits were built using the same construction guide. The two layouts are virtually identical. The only difference between them is the type and orientation of the transistor.

The terminals are a good set of reference points. To fit them - you may need to enlarge the holes slightly. Then turn the board over and use a felt-tip pen to mark the 17 places where the tracks are to be cut. Before you cut the tracks - use the "actual size" drawing to Check That The Pattern is Correctly Marked .



Light Controlled Relay 
Pattern For Cutting The Tracks


Actual Size


Stripboard 
    - Actual Size -


When you're satisfied that the pattern is right - cut the tracks. If you don't have the proper track-cutting tool - then a 6 to 8mm drill-bit will do. Just use the drill-bit as a hand tool - there's no need for a drilling machine. Make sure that the copper strip is cut all the way through. Sometimes a small strand of copper remains at the side of the cut and this will cause malfunction. Use a magnifying glass - and backlight the board. It only takes the smallest strand of copper to cause a problem.

Next - fit the Seven Wire Links - the preset - and the two fixed resistors. For the links - I used bare copper wire on the component side of the board. Telephone cable is suitable - the single stranded variety used indoors to wire telephone sockets. Stretching the core slightly will straighten it - and also allow the insulation to slip off.


Light Controlled Relay - Make A


Next - fit the diode and the two capacitors. Pay particular attention to the orientation of the diode. See the Photograph Of The Prototype. Then - fit the relay - the IC socket - and the LDR.


Light Controlled Relay - Make B


Turn the board over and examine the underside carefully - to make sure that there are no unwanted solder bridges or other connections between the tracks. If you backlight the board during the examination - it makes potential problem areas easier to spot. When you're satisfied that everything is in order - add the 6 solder bridges.


Light Controlled Relay - Make E


Fit The Transistor

So far - the construction of both Circuits 1 & 2 is identical. All that remains now is to fit the correct transistor. For Circuit No.1 - it's a PNP transistor. For circuit No.2 - it's an NPN transistor. Note that the transistors face in opposite directions. In Circuit No.1 - the BC557 faces left. And in Circuit No.2 - the BC547 faces right.


Circuit No.1 - BC557 PNP

Circuit No.1 - Photo

BC557



Circuit No.2 - BC547 NPN

Circuit No.2 - Photo

BC547

Finish off by inserting the Cmos IC into the socket. Pin 1 of the IC should be in the top left-hand corner. Check that all 14 pins have entered the socket. Sometimes - instead of entering the socket - a pin will curl up under the IC.



You Are Now Ready To Test Your Finished Circuit Board.

Relay Circuits
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The Rest of Ron's Circuits Write To Ron More Free-to-Use Circuits Circuit Exchange International