The PotLock

this is a 3 digit combination lock with potentiometers, logic gates and differential comparators

Connection Diagram and Parts

i use (take a look at the links)

6 resistors 10k

6 potentiometers 100k

the voltage is 5v DC

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)

if you want to see how the circuit works use leds at lm3391,74HC021,74HC10 outputs like the picture

print the numeric pads for the potentiometers for easiest setting of the combination

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...