this is a 3 digit combination lock with potentiometers, logic gates and differential comparators
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Step 1: Connection Diagram and Parts
Step 2: How Its Works
with the Differential Comparators you can compare different voltages
look the diagram for the connections
if the lm339 output 0 is on
so i use NOR gates,i connect the outputs from comparators to the NOR inputs
and the 3 outputs from the NOR gates to the inputs of a triple NAND gate
when the left potentiometers are at the same position with the right potentiometers
the output is 0 (ON)
(LOOK THE TRUTH TABLE)
Step 3: Leds
if you want to see how the circuit works use leds at lm3391,74HC021,74HC10 outputs like the picture
Step 4: The Combination
print the numeric pads for the potentiometers for easiest setting of the combination
Step 5: End
you can use it just for education or you can lock something like box with a magnetic lock, add at the output a
PNP transistor with a relay or a N-Channel mosfet to control bigger loads than one led...