Electronic Project Description
Pin-pad based access control system using programmable RAM.
using a promagable 8 digit nemuric code to activate an electromagnetic door
latch opening the door. It is not DIP Switch based combination lock but
a fully programmable digital lock.
Now a days due to advent of microcontrollers projects like these have become very simple.
Back in 2002 and 2003 when microntrollers were out of my reach and imagination, this project
was a lot challenging.
It uses a 74HC series keypad encoder(Keypad to Hex converter). A 4 bit digital comparator,
2 decimal 8 counters(Ex.4011), a volatile RAM chip and few logic gate IC.
A switch was used for program and operation mode and a 4.5V battery pack for powering up the RAM
in case of power failure.
In operation mode, when a key is pressed, its equivalent Hex is send to the comparator together with
incrimenting the RAM address in data read operation. If the data from the RAM matches the keypad input
then the counter is incremented by one, wrong input resulting in negative comparator output resets the counter,
upon eight such increments a relay is triggred for activating the door latch momentarily.
switch was installed to detect the position of the door.
The circuit was taken from EFY. The PCB was ordered from Kits and Spares as it was to intricate
at that time to make at house.
A suitable metal housing is provided with voltage protection and 12V relays and battery pack.
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