4 Digit Alarm Keypad

Posted on Apr 18, 2012

The Keypad must be the kind with a common terminal and a separate connection for each key. On a 12-key pad, look for 13 terminals. The matrix type with 7 terminals will NOT do. The Alarm is set by pressing a single key. Choose the key you want to use and wire it to `E`. Choose the four keys you want to use to switch the alarm off, and connect them to `A B C & D`. Your code can include the non-numeric symbols. With a 12-key pad, over 10 000 different codes are available. Wire the common to R1 and all the remaining keys to `F`. When `E` is pressed, current through D2 and R9 switches Q5 on.

4 Digit Alarm Keypad
Click here to download the full size of the above Circuit.

The relay energises, and then holds itself on by providing base current for Q5 through R10. The 12-volt output is switched from the "off " to the "set " terminal, and the LED lights. To switch the Alarm off again it is necessary to pre

Leave Comment

characters left:

New Circuits



Popular Circuits

Stereo Mixer With Pan Controls
studio synth circuit
Automatic Switching-on Emergency Light
CD4040 Generating Long Time Delays Circuit
Tesla Coils
00 to 99 minute timer using PIC16F628A microcontroller
tda7560 4 x 50 watt bridge
Up/Down Timer For A Power Antenna
Human biological signals consisting of a preamplifier circuit INA102
Trap MC33171
Based LMD18245 bipolar stepper motor control circuit diagram
Temperature compensation of the symmetrical power supply 7812 F007C