So to save power, you could likely use a sensitive optocoupler (such as a 4N32 with a darlington output) instead of an SSR.

 

I suspect you can drive this directly with a PIC output. This seems to be a very low power device, so the current is likely way less than it's 20mA limit. Just attach the blue wire to PIC ground and the PIC output to the red wire. The PIC output should be set to input when you want it inactive, then set to output outputting a zero to activate it.

Check the voltage and the current of the red and blue wires. If voltage is less than the Vdd of the PIC, and current is less than 20 mA, it should work okay.

Bob

 

Some OPTOMOS relays have LED currents on the order of 1 mA.

 

It is kind of hard to get hard specs out of this discussion but I will throw out one component which gives a switch closure with very low average power and provides isolation. The "latching signal relay". A short pulse turns it on and a short pulse switches it off. It can be on for days (or forever) with no power consumption. The small latching relays are used for data acquisition, medical equipment, etc. Panasonic makes some small ones with low coil voltages (3V). This kind of thing:

https://www.mouser.com/datasheet/2/315/mech_eng_txs-1299315.pdf

Someone needs to do the table showing worse case, on-off duty cycle and power consumption for each approach.

 

I think the OP is saying the output can come on up to 15 times a day. For the latching relay, it does not matter how long the output is on. Just the amount of energy to turn it on and then turn it off. So, 15 times day with 2 pulses each time is 30 pulses per day. The energy in each pulse is approximately 0.05 amps (coil current) at 3 volts (coil voltage) for 0.05 seconds (pulse width) or 0.05 x 3 x 0.05 = 0.0075 joules per pulse or 0.0075 x 30 = 0.225 joules per day. Note, the pulse width is 10 times the activation time of the relay. 5 times is common and 10 times is conservative. So, how do other switching methods compare to 0.225 joules per day? I don't know how important is isolation from the postings but the relay is completely isolated. Finally, be careful, the relay can have environmental restrictions such as vibration.

A super low power optocoupler with an average on time of 3 minutes, 15 times a day might be 0.001A x 3V x 180 seconds x 15 = 8.1 joules per day. Am I correct about this energy business?

 

Don’t know why everyone is obsessing about isolation between two low voltage battery powered devices.

Can someone please telll me why my suggestion wouldn’t work?

Yes, I understand that using the MOSFET in the PIC would not work, if, for example, the “switch” is switching AC, but this seems highly unlikely.

Bob

 

Use an MCU with an RTC.