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

Tone generator with 555
12v to +5V, -12V, +12V, +24V adaptor
High power bug
SEM/STEM detectors and CRTs
PreamplifierCircuit DCF77
wire three-way circuit between two buildings with only 3 conductors
TV Transmitter Audio and video IC LM1889
jung schematic
Digital frequency counter
Flashlight circuit diagram of a motor control model
Using C-MOS light emitting diode drive circuit NAND gate pulse
5G14D + 24V 1.9A power supply
D2025 dual-channel audio amplifier circuit diagram