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Comment by heffer | Hacker News Reader

Now that's a blog post I'd read.

It's actually pretty straightforward: just wire in the relays (shift register required for ESP8266) then turn them on and off as desired. With your valves exposed via wifi to Home Assistant or MQTT the world is your oyster as far as using inputs (weather, rain, etc) to bring intelligence into your irrigation scheduling. I loosely followed this guide when I built mine: https://selfhostedhome.com/diy-wifi-sprinkler-controller-usi...

> shift register required for ESP8266

Why? A D1 Mini has 8 Digital I/O ports that could drive a 3.3.v relay module.

Not sure, I didn't try, but using one was a good excuse to learn how. The blog post suggests that despite there being 8 they're not all suitable for use (maybe due to high on boot or something)

Ah... that makes sense. It looks like IO0 needs to be pulled high to boot.

Still looks like you could redefine RX to a GPIO and still have 8 if you didn't need serial input. I vaguely remember running into this issue with some load cell AMPs.

A Shift Register or IO Expander seem like the more interesting and less frustrating route. I'd probably end up using an ESP01 and i2c IO Expander because I'm a masochist and love trying to squeeze as much as I can out of the ESP01.

I actually referenced tamu_nerd's link below, but my approach was simpler as I used an ESP32 (more pins, so no shift register needed), and I powered the ESP32 with its own USB charger (so no AC to DC converter needed). I can add something to GitHub and will reply here)

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