I've always wondered how did electronic locks work, so once i finished the basic digital electronics course I decided to build one myself. And I´ll help you to build your own!
You could connect it to anything from 1v to 400v(or maybe more that depends on the RELAY), DC or AC, so you could use it to control another circuit, or even to electrify a fence!! (please dont try that, really dangerous)… I connected a mini chrismas tree to the output (110v) cause I hadnt taken the holydays decoration off my lab, so it was around at the time i finished the proyect.
Here are some pictures of the finished System, and a video too, so you can see it working.
Step 1: How does it work?
- First we need a circuit to decode the 10 possible inputs (0-9) to its 4 output BCD (Binary Coded Decimal), and another output that tells us when any button is pressed.
- Then we need to build the circuit for our two 7-segments displays to work properly, with 4 inputs for a BCD number and of course 7 outs for our displays, ( I used the IC 74LS47)
- Then a circuit to save each pressed number and toggle between displays
- As well as an internal memory for our password
- And, the hearth of our lock, the comparator (its 8 bits ´cause there are 4 bits per digit in the display, meaning that if you want to do a 4 digit lock you will need two of this connected together.) This will tell us if the numbers in the displays are the same as the password saved in the internal memories.
- And finally a circuit to keep the OPEN or CLOSE signal for an undetermined time, and of course an output (thats whatever you want to control with your lock)