Bear in mind I already had irrigation system with 24v valves in place. The <$20 is the adding the ESP32 , 8 switch relay rail, plus the plexiglass, standoffs, and USB charger.

Ah alright that's more believable, though still quite a bargain.

The thing you have to understand is that controlling an irrigation system is easy, the valves work just like light switches but on lower voltage.

The cost of an irrigation system is making it user friendly for a customer.

Example: https://www.amazon.com/Hunter-Sprinkler-XC400-4-Station-Cont...

Like the OP's solution, it is a microcontroller hooked up to a relay array, but it also has:

* AC/DC Transformer

* Real-Time-Clock

* Battery backup

* User Interface

* Secure, weather proof housing

* Printed Instructions

And it costs less than $90. They're making a profit on them, so the BOM is probably closer to $20-30.

The solution is completely plug-n-play compared to building from scratch, setting up a home automation system, and programming a microcontroller.

> With how much ESPs go for right now I kinda doubt that

D1 Minis are like $1.50 and ESP01s are $0.95.

Good luck controlling an 8 pin relay with 4 accessible pins hah.

The 01s are cheap for a reason - they're useless for most projects, hell I'm always running out of pins even on the esp32-cams.

The ESP01 works perfectly for most sensor projects. It can handle I2C and serial IO simultaneously.

If you really need more GPIO you can get an I2C based IO Expander to add 10 more GPIO.

Meh, those cost extra and don't really do analog in or PWM out and have dreadful response time. Plus you have to deal with i2c which adds complexity.

I suppose in this case you could do it in that roundabout way by stacking two of those for relay control since it's as basic as it gets.

Do you mean this? https://www.amazon.com/CANADUINO-WEMOS-Minikit-240MHz-Blueto... because it has a lot more than 4 accessible pins.

Nope, I mean this: https://www.amazon.com/MakerFocus-Wireless-Transceiver-DC3-0...

8 pins, half of those gnd, vin, reset, and something else. 4 are usable I think.

That's an ESP-01. It has 4 GPIO with some restrictions but you are able to simultaneously run an I2C bus and Serial bus giving you tremendous flexibility.

You can get those in bulk for less than a dollar each and are my most used microcontroller. They're so easy to deploy and ear easily powered of USB wall warts with a regulator.