How To Build A Simple Code-Operated Switch


Posted on Feb 6, 2014

This is a simplified version of the Universal Keypad-Operated Switch. I have modified the design to reduce the complexity of the circuit - and the number of components required. As a result - the code is somewhat less secure. However, there should be lots of situations where it will still be adequate. The circuit is drawn with a 12-volt supply -


How To Build A Simple Code-Operated Switch
Click here to download the full size of the above Circuit.

but it will work at anything from 5 to 15-volts. All you have to do is choose a relay suitable for the supply voltage you want to use. Replace the SPCO/SPDT relay with a multi-pole relay - if it suits your application. Do not use the "on-board" relay to switch mains voltage. The board`s layout does not offer sufficient isolation between the relay contacts and the low-voltage components. If you want to switch mains voltage - mount a suitably rated relay somewhere safe - Away From The Board. Choose the four keys you want to use as your Code - and connect them to "A B C & D". Wire the common to R1 and all the remaining keys to "E". The circuit will power-up with the relay energized. To de-energize it - you must enter your code. To re-energize it - press any of the keys connected to "E". To reverse the operation of the circuit replace Q2 with a BC547. With an NPN transistor in this position - the circuit will power-up with the relay de-energized. To energize it - you must enter your code. To de-energize it again - press any of the keys connected to "E". Any keys not wired to "A B C & D" are connected to the base of Q1. Whenever one of these "Wrong" keys is pressed - Q1 takes pin 1 low and the code entry sequence fails. If you make a mistake while entering the code - simply start again. 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...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    120 and 240Vac LED Indicator
    Cold Atom Control System for PC
    Signal and Tone Activated Relay Switch
    Digital Vacuum Gauge
    Arduino While Loop
    Motor Controller
    mic circuit
    Sound Level Indicator
    FM Receiver Circuit
    fm generation using 555 timer
    PWM power controller
    OCL AC negative feedback amplifier analysis
    Common emitter amplifier works a



    Top