Free Details Of How To Build A Simple Keypad-Operated Switch - Using Cheap Off-the-Shelf Components.
COMMENTS Homer SUGGESTIONS

Universal Keypad Switch - Support Material

MORE KEYPAD CIRCUITS

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Circuit Description

Click Here For A Photograph Of The Prototype.

Circuit Diagram For A 
Keypad-Operated Switch

Click Here To Learn More About The Complementary Latch.


DANGER
Do not use the "on-board" relay to switch mains voltage. The board's layout does not offer sufficient isolation between the relay contacts and the low-voltage components. If you want to switch mains voltage - mount the relay somewhere safe - Away From The Board.


Parts List

Parts List For The
Four-digit Keypad


Suppliers Worldwide
RS Components
Uk & Ireland
Maplin


Construction

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

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 30 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 .

When you're satisfied that the pattern is right - cut the tracks. Make sure that the copper 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. 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.


Pattern for Cutting
The Tracks on the
Underside of the Board

Actual Size Of Pattern

Pattern for Cutting
The Tracks on the
Underside of the Board
ACTUAL SIZE



Next make and fit the Fourteen Wire 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.

Add The Fourteen Wire Links


The next stage is to fit the 11 resistors. The resistors are all shown lying flat on the board. However, those connected between close or adjacent tracks are mounted standing upright. See The Photograph Of The Prototype.

Add The Eleven Resistors


Now fit the transistors and diodes. Note that the PNP transistor is the one with its emitter arrow coloured red. And note that D2 is mounted standing upright. See The Photograph Of The Prototype.

Fit The Transistors And Diodes


Fit the Capacitors, the IC Socket and the Relay.

Add The Capacitors
The IC Socket And
The Relay


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.


Add The Solder Bridges To
The Underside Of The Board


Finish off by inserting the Cmos 4081 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.



Test Your Finished
Circuit Board
Three Ways
To Modify The Circuit
Add A Beep
To The Keystrokes
Add A Tamper Alarm
To The Keypad



Keypad Layout

Construction 
Of Keypad


General Information

General Information


Test Your Finished Circuit Board

Schematic Diagram And Layout The Rest of Ron's Circuits Write To Ron More Free-to-Use Circuits Circuit Exchange International