Now here’s a digital lock unlike any other, as it has only two buttons instead of the usual numeric keypad. The way it works is as simple as its keypad. Button S1 is used to enter the digits of the secret code in a pulsed fashion-i.e. the number of times you press the but-ton is determined by the digit to be entered. A dial telephone uses the same type of coding (now maybe there’s an idea?). Press four times for a 4, nine times for a 9, etc. Pressing button S2 indicates the end of a digit.
Project Image :
Two-button Digital Lock Project Image
For example, to enter the code 4105, press S1 four times, then press S2, then S1 once, S2 once, then without pressing S1 at all, press S2 again, then finally S1 five times and S2 once to finish. If the code is correct, the green LED D1 lights for 2 seconds and the relay is energised for 2 seconds. If the code is wrong, the red LED D2 lights for 2 seconds, and the relay is not energised. To change the code, fit a jumper to J1 and enter the current code. When the green LED D1 has flashed twice, enter the new 4-digit code. D1 will flash three times and you will need to confirm the new code. If this confirmation is correct, D1 will flash four times. If the red LED D2 flashes four times, some-thing’s wrong and you’ll need to start all over again. To finish the operation, remove the jumper and turn the power off and on again the digital lock is now ready for use with the new code.
Circuit diagram :
Two-button Digital Lock Circuit Diagram
The software can be found on the webpage for the project [1]. Don’t forget to erase the microcontroller’s EEPROM memory before programming it, so you can be sure that the default code is 1234 and not some -thing unknown that was left behind in the EEPROM. A little exercise for our readers: convert this project into a single-button digital lock for example, by using a long press on S1 instead of pressing S2 to detect the end of a digit.
Author : Francis Perrenoud - Copyright : Elektor
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