Well, I'm back working on my irrigation sensor. I have reworked my board a bit, removing the connections an d resistors for the last two positions. I only needed 12 and I have room for 16 so I am converting two to use for my reed switch. From our discussion earlier, I've decided to use a separate 5 vdc circuit for the reed switch and so have removed the resistors to pins 1 and 4 of the A3700 that were to detect 24 vac. I have tested two 47 ohm resistors to pins 2 and 3 and they detect 5vdc just fine. The reed switch is at the end of a 100 ft (30m) shielded cable.
I am wondering if I should put the reed switch between the 5vdc source and the positive pin of the A3700 or if I should put it between the negative pin of the A3700 and ground. In the normal operation, it seems like it would make no difference but perhaps there is a convention or best practice that would prefer it on one side or another.
BTW, my two port 5 vdc power supply has no ground with regard to its 120 vac plugin. I will run the Raspberry Pi on one port and have the other port provide voltage to two reed switch circuits. The two reed switch will never be counting pulses at the same time but I suppose they could be left in a closed state when the circuit switches from one bank of 6 water valves to another.
If anyone has a comment on this I would be grateful to hear it.
In the diagram, the reed switch is connected to the 5v from the Raspberry pi but in my circuit, I will have it on a separate 5vdc power supply. This is not relevant for my question though. There is also a 5.6v zener diode to serve as an overload protection.