I started a company that constructed booths which used 70 accurately sync'd Pis with custom PiCams (fitted with lenses) to take pictures of human subjects, for turning them into avatars like this: https://maintenancearistonalex.blogspot.com/2019/06/blog-pos...

At the beginning of the project, I'd barely powered up the Pis I had collecting dust in my drawer. By the end, I was a legitimate domain expert in several niches within niches of Pi dark arts. For example, since Pis do not have hardware clocks, you have to rely on NTP. However, you need to take pains to make sure that each Pi is getting the same amount of voltage or else they will run at different speeds. If you want to power 70 Pis in a constrained space, you need to devise a customized power distribution system with adequate heat venting.

https://indesitmaintenance.blogspot.com/2019/06/blog-post.ht...

Due to the thin effect, voltage drops over distance, so the distance a Pi was from the power would impact the voltage and therefore the speed. The major breakthrough came when I realized that I could start with a high end power supply outputting 14 volts and terminate each parallel line with a device known as a UBEC. They are used primarily by drone enthusiasts to make efficient use of battery packs.

A UBEC is designed to drop down a supply voltage to 5v without bleeding off the excess voltage as heat. Since this could also describe a fuse, we felt comfortable bypassing the Pi's MicroUSB power supply and attaching the UBEC's pins directly to the top pins on the Pi's GPIO breakout.

That's just a tiny example of the hijinx. The Pi is an incredible tool if you're patient and clever.

What a rollercoaster.

user:	tnasemelward
created:	June 25, 2019
karma:	3