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 …

…Hz. 6.<Tab/>Our RC out from pin 15 on our 74160 (1Hz) feeds into the enable (T&P) of our 74160 (LSD). 7.<Tab/>The 7447 7-segment decoder is a special decoder that converts a 4-bit binary coded number into 7 outputs. The seven outputs are specially coded to display the input decimal code. *8.<Tab/>Finally the 7447 controls the 7 segment display to display the appropriate count state.