So the Arduino, along with other brands such as the Pi, have always interested me but I could never justify buying one as I could never come up with something to build around it, but just recently that has changed as our thermostat for the house has gone out and I quickly learned they are extremely simple devices. More or less just three 25VAC relays, one for fan, one for heat, one for cool, along with a temperature sensor. So I bought a Arduino Nano with the ATmega328 as this seems to be between middle and top end as far as Arduino boards go along with being very tiny while still having a USB port to make connecting to it easy. Both of which were important to me.
The thermostat ended up getting replaced for free thanks to Home Depot being nice and honoring a 90day warranty that ended over a year ago but I still want to try this for some fun. So I guess I'll just list my questions and let you guys have fun with it...
- What are good and very small relays that can handle 25VAC at up to 1A and is there such a relay that has three positions? As Heat and Cool will never be on at the same time. This way I'd have one relay for the overall mode (Off/Heat/Cool) and one relay for the fan (Auto/On). There was only one relay on the old thermostat I had but I returned it before thinking to get its part number, all I remember was it having 8pins and looked like only 5 were used.
- What would be a good display for text only? I'd love to go all out and have an e-ink or OLED screen that has touch but I hear displays get complicated real fast and I'm pretty sure that's above my capabilities for now, plus I'm not sure if this Arduino could handle even a small low resolution color screen with touch, but I haven't looked into that. So I'd like it to be nice looking, but at the same time if there's a display for beginners I probably will want that more.
- Can I just grab any temperature sensor from RadioShack for 99cents or is there something you guys recommend?
- As it can not take the 25VAC from the HVAC system, this completes the circuit and tells it to turn heat, cool, and/or fan on, I'd like to power this by battery. Thus I'm interested in an e-ink or OLED display and if there are such relays that don't require constant power to keep the relay enabled. Along with any other power saving ideas. Unless this could last for a long time on a battery of some sort or you guys know a way to use that 25VAC without turning the HVAC on and having a big transformer for 25VAC to 5VDC?
- As my first step I plan on just making a manual thermostat, but if I ever feel like going the next step and making it run on schedules and maybe have stuff like total time the heat, cool, and fan were running is it capable of keeping the time? I ask because I see a lot of talk about real-time clock shield addons and such.
I think that covers all my basics. I'm sure parts of this will be over my head as I don't have a ton of experience with microcontrollers but where's the fun if everything is a breeze.