>Pi with Wifi and a
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My original plan included an existing ESP8266 for Internet so I won't need that any longer. Any reason for the Zero over the 3 B+?
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I purchased both but would love to have someone else's opinion on the right solution here.
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>12v-capable relay HAT
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I haven't ever heard of a relay HAT so I'll have to google it. I bought a bunch of these for the relay: https://www.amazon.com/gp/product/B00ZR3B252/ref=ppx_yo_dt_b_asin_title_o05_s02?ie=UTF8&psc=1
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>plus a cheap USB power-bank
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I planned on using AC power (w/ a DC converter) to supply power to the relay and I assumed if I used a power supply module or something like that I could just grab 5v off that to power the Arduino and then the usb client would get it's power from the MCU.
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I've never messed with the Raspberry products so I'll probably have to re-investigate power options. One problem at a time I suppose - thank you for your advice.