Build this Four-Digit Keypad Operated Switch using off-the-shelf components. Although it was designed to control a Burglar Alarm - it has other uses.
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Four-Digit Keypad - Support Material

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KEYPAD CIRCUITS

Four-Digit Keypad Schematic The Rest of Ron's Circuits Write To Ron More Free-to-Use Circuits Circuit Exchange International
Add A "Beep" To The Keystrokes Three More Ways To Modify The Circuit

There is both a Four-Digit and a Five-Digit version of this switch. Although they will have other applications, both are designed to control the Modular Burglar Alarm circuit. Simply use the relay's changeover contacts in place of SW1. The poles and the points marked 'set' and 'off' represent the corresponding connections on both the keypad relay and the alarm switch. Click Here for a Diagram.


Circuit Description

Click Here For A Photograph Of The Prototype

Circuit Diagram For
An Alarm Control Keypad



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 29 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 Fifteen 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 Fifteen Wire Links



The next stage is to fit the 11 resistors, the 5 capacitors and the IC socket. Using a socket reduces the chances of damaging the IC; and makes it easier to replace if necessary. The components are all shown lying flat on the board. However, those connected between close or adjacent tracks are mounted standing upright.

Construction Of The
Circuit Board - Continued

Now fit the transistors, diodes and relay. Again, the diodes are all shown lying flat on the board. However, those connected between close or adjacent tracks are mounted standing upright.

Next - 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 7 solder bridges to the underside of the board. Pay particular attention to the bridge that joins pins 4 & 12 of the IC. When positioning the bridges - it may help to make a copy of the above drawing - and flip it left to right.

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.

You're Now Ready To Test Your Circuit


Keypad Layout

Construction 
Of Keypad


General Information

General Information

Add A "Beep" To The Keystrokes Three More Ways To Modify The Circuit
Four-Digit Keypad Schematic The Rest of Ron's Circuits Write To Ron More Free-to-Use Circuits Circuit Exchange International