Simple combination lock


Posted on Feb 7, 2014

This experiment may be built using only one 8-position DIP switch, but the concept is easier to understand if two switch assemblies are used. The idea is, one switch acts to hold the correct code for unlocking the lock, while the other switch serves as a data entry point for the person trying to open the lock. In real life, of course, the switch a


Simple combination lock
Click here to download the full size of the above Circuit.

ssembly with the "key" code set on it must be hidden from the sight of the person opening the lock, which means it must be physically located elsewhere from where the data entry switch assembly is. This requires two switch assemblies. However, if you understand this concept clearly, you may build a working circuit with only one 8-position switch, using the left four switches for data entry and the right four switches to hold the "key" code. This circuit illustrates the use of XOR (Exclusive-OR) gates as bit comparators. Four of these XOR gates compare the respective bits of two 4-bit binary numbers, each number "entered" into the circuit via a set of switches. If the two numbers match, bit for bit, the green "Go" LED will light up when the "Enter" pushbutton switch is pressed. If the two numbers do not exactly match, the red "No go" LED will light up when the "Enter" pushbutton is pressed. Because four bits provides a mere sixteen possible combinations, this lock circuit is not very sophisticated. If it were used in a real application such as a home security system, the "No go" output would have to be connected to some kind of siren or other alarming device, so that the entry of an incorrect code would deter an unauthorized person from attempting another code entry. Otherwise, it would not take much time to try all combinations (0000 through 1111) until the correct one was found! In this experiment, I do not describe how to...




Leave Comment

characters left:

Related Circuits

  • New Circuits

    .

     


    Popular Circuits

    Stereo PLL FM transmitter
    Atari 2600 CE
    RS232 transceiver circuits
    Schematic Audio Power Amplifier with IC TDA2612 Schematic Diagram
    adjustable current limiter circuit
    on off relay circuit automatic
    battery isolator
    Wire loop alarm
    The Measurements for MIT 3DL1 Run
    LM741 OpAmp Voltage Indicator
    LIGHT SEEKING ROBOT
    Infrared Wireless Headphones circuit
    DC supply voltage the more limited indication circuit



    Top