> RaspberryPies and such are commodity hardware. You can buy one, two, ten, twenty, a hundred, and it just scales along.

Not my experience at all. Pies are hard to find, get more expensive each week. Some are impossible to find (Pi zero).

The most fragile part of a phone is the screen. If you don't care about breaking it, then access to the battery becomes pretty easy, and therefore easy to replace.

  A bird [redacted] bush.

Phones are pretty robust though, meant to handle everyday use and abuse. In terms of failure, the battery is really the only thing to be concerned about. Most phones have some battery limiting option, and bypass the battery when the charger is connected. And if you're determined enough you can run without a battery.

Hobbyist don't usually need to scale beyond one device. Warranty is not that a big issue, if you buy a used hardware you know what are getting into, that's why they are cheaper than new devices.

I've chatted to the guy running Citronics, they provided old but working Fairphone 3 to a workshop we had at Goatmire Elixir. They try to tackle repurposing and certifying the quality of old phones. Interesting effort and well positioned for the current climate.

Their board currently on sale is this. Based on Fairphone 2. Targeting commercial or industrial more than hobbyist though. I've been trying to convince them to sell the old phones as is, as well. https://shop.citronics.eu/

Thanks to Marc Lainez and his token spend we have a great Nerves system for running the Fairphone 3 by just programming Elixir. And people are flipping new (old) phones over to be put to work every week in the Nerves Discord.

We have a good UI framework in Emerge. We have media handling with Membrane. And Nerves handles the OS integration for stuff like networking. I thoroughly enjoy making up my own mobile OS for my own purposes.

You lose the GPIO/I2C/SPI/UART as easy extension points compared to the Pi. But the stuff that is there is already well integrated.

You could go a step further and just buy low-end new phones. They are available at sub-$50, which is near the price of Raspberries.

The main issue with old phones are NAND Flash degradation and battery problems. As long as you fix those two issues everything else is simple. These days with AI it's almost trivial to build and flash your own ROM and even the most hardcore of binary blob drivers can be reversed so long you have enough GPUs.

It's not the dark days of android where something like CyanogenMod takes a whole team of experienced system and embedded engineers to port and you don't have to hunt for information on XDA anymore.

Oh and cooling. That's something that the Pi has an edge on.

Early Android hackers might remember something called the Android Arduino Mega ADK. I suspect nowadays if you need real time control you can probably just have smartphone control the peripherals via the ESP32 using either USB C or Bluetooth. Developing over the wire protocols is trivial since LLMs can hammer out protobuf definitions like there's no tomorrow.

for applications like that your should remove the battery and put small cheap circuit that emulates it. then you can run such server very very safe, unlike with 100x batteries always harging.

Bot farms works that way.

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