Since we are mulling over various power switching options, it might be useful to see how many microprocessor pins and switches (relay/SSR) we need at this point...
Maybe an initial tally could be useful.
Quote:
Originally Posted by AC_Hacker
As for myself, I would like a GSHP controller that, as a very minimum requirement would: - Provide for a startup delay of the compressor
- Monitor the output of the evaporator HX
- If evaporator HX output temp was equal to or less than 37F the compressor would shut down for a selectable period off time (10 minutes for starters) while the water pumps keep running
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1. startup compressor: I think an SSR for this output (digital-out pin for the micro) SSR has opto-isolator
2. monitor output: needs an analog-in pin to read a thermistor, or a digital-in pin to read a 1-wire sensor (and 1-wire library)
Quote:
Originally Posted by jeff5may
...In addition to AC's requirements, I would like the controller to do these things: - Have the option for reverse cycle (heating and cooling modes)
- Short cycle protection (compressor lockout)
- Air or water source operation (selectable or configured)
- Freeze protection (water source) or defrost (air source - compressor lockout or active reverse cycle)
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NOTE: My requirement for HX monitoring = your 'freeze protection' and your need for 'defrost sensing' = my 'freeze protection', so depending on the application, these functions are so similar the we could use the same hardware, and maybe sufficiently similar software, so that some variable(s) could be switched to tailor behavior.
3. Reverse cycle: this would call for two digital-out pins, and two relays
4. Freeze protection: this would call for a sensor pin (analog-in or digital-in)
You didn't mention it, but if your unit is going to be outside, you may need a crankcase heater, which would add:
5. thermistor or 1-wire sensor and an analog-in pin or digital-in pin. since we've previously call out a 1-wire library, no need to repeat.
6. digital-out pin and a SSR or fairly beefy relay.
Quote:
Originally Posted by jeff5may
I suggest we include a few "sugar cube" relays to directly control smaller devices, such as fans, pumps, or valves.
To control components that require more current than the relays can supply, a contactor or SSR can be added into the circuit. For that matter, the contactor or whatever can be wired to slave off a sugar cube relay.
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7. fan control: digital-out pin & relay
8. pump control: digital-out pin & relay
9. valve out control: digital-out pin & relay
10. Contactor: difital-out pin, relay, contactor (this may be the same as my item #1?)
jeff5may, in previous conversations, you said you wanted a read-out display
Do you still?
That could call for:
11. a LCD display unit which could call for an LCD library, I2C library (maybe), 1 digital out pin with I2C option, or maybe 6 digital-out pins for direct control option.
12. Should we include an Arduino Uno?
What am I missing so far?
There is a possibility that as this design develops, it may become complex enough that some of the functions could be handled by slave processors, like a Teensy or equivalent, saving pins and program space for the main micro-brain.
-AC