Experiment 23 of Make: Electronics uses 74LSxx chips (TTL chips) instead of the 74HCxx (CMOS) that has been used in previous experiments. In the first part of this experiment a simple binary counter in made (figure 4-102). I ordered some low current LED’s especially for this experiment to be able to see the output of the circuit. The circuit, with three binary output pins connected to a LED, can count from 0 (000) to 5 (101).
I encountered no problems building the circuit and with the low current LED the output was clearly visible. The only detail that puzzles me is that the 74LS92 counter has a Clock input B (pin 1) and Clock input A (pin 14). The output from the 555 chip (pin 3) is connected to Clock input A nevertheless Clock input B needs to be connected to Binary output A (pin 12) of the 74LS92 counter. Anyway everything works fine.
|Breadboard with the binary counter. The 74LS92 counter (left) is triggered once every second by the 555 chip. The three LED on the left indicated the output from the counter.|