How Digital Count-Down & Count Up Circuits Work

Theory of Operation
<Tab/>One common requirement in digital circuits is counting, both forward and backward. Digital clocks and watches are everywhere, timers are found in a range of appliances from microwave ovens to VCRs.
This circuit is used as a counter. The two 7-segment displays (1 least significant digit, and 1 most significant digit) count up (LSD = 1/10 sec, MSD = 1/100 sec). The least significant digit's output (carry out) feeds into the most significant digit input.
1.<Tab/>555 monostable multivibrator creates 320Hz.
Monostable multivibrator often c…