The counter is used to count the pulses that are generated by the 555 chip. The 555 chip for this project is producing a pulse every 80 ms. The counters that are being used are SN74LS161. These counters are 4 bit binary counters. Therefore, each chip will count up to (1111 in Binary) 15 pulses and send a pulse of their own. When 4 of these counters are set up in series, the last chip will send its pulse after about 4050 seconds or 67.5 minutes. The pulse that is sent out after the last chip reaches a count of 15, will flip the flip-flop and turn off the solenoid valve.
Note: One of the most important things that a designer can get his hands
on are the data sheets for the chip. They were very helpful and gave me
some guidance.
Data
Sheet for SN74LS161 (pdf format)
The wiring diagram for the counters is found in Figure 1.
As seen in figure 1, the pins that are used for the counters are CP (pin 2), TC (pin 15), PE (pin 9), and MR (pin 1). CP is the input for the counter. TC is the output for the counter. It is used to send a pulse to the next counter or to the flip-flop. PE is a pin that needs to be at 5 V DC for the counters to operate.Figure 1. Wiring diagram for the counters.