This simple counter can be used to count pulses, as the basis for a customer counter (like you see at the doors of some stores), or for anything else that may be counted. The circuit accepts any TTL compatible logic signal, and can be expanded easily (see Notes). Circuit diagram
 7 Segment Display Reference
 Parts:
R1-R7 470 Ohm 1/4 Watt Resistor
U1 74LS90 TTL BCD Counter IC or 7490,74HC90
U2 74LS47 TTL Seven Segment Display Driver IC or 7447,74HC47
DISP1 Common Anode 7 Segment LED Display
MISC Board, Sockets For ICs, Wire Notes:
1. All pulses to be counted are to be TTL compatible. They should not exeed 5V and not fall below ground.
2. You can add more digits by building a second (or third, or fourth, etc...) circuit and connecting the pin 11-6 junction of the 74LS90 and 74LS47 to pin 14 of the 74LS90 in the other circuit. You can keep expanding this way to as many digits as you want. author:,
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