27th Nov 2015
or “How I Fell in DooDoo and Came Up Smelling of Raspberries”
OK. Picture the scene. It’s late on a Friday night, and you’ve been hacking on your Pi Wars robot all evening. It’s been productive. Between you and co-roboteer, you’ve ironed out glitches in your Remote Control code, you’ve soldered up the wiring looms, and you’ve even designed and printed custom parts to mount the pi onto the baseplate you laser cut earlier. You’re robot building machines. Go you. High fives all round.
Flushed with success, you both decide to power up the pi and and take it for a spin. So, you plug in the USB cable that you wired up to that adjustable 5v regulator earlier to step down the power from the lipo battery, and… uh. I’m pretty sure the activity light doesn’t normally do *that* when it’s booting. what the..? yank the power! yank the freaking power!
Welcome To Cockupsville. Population: You
OK. wait a second. what just happened? Well, remember that 5v regulator you wired up earlier? The key word there was adjustable, Dingus. And you didn’t check it, did you? You buzzed every single other thing you soldered, but you forgot to check that the output voltage was actually, y’know, ADJUSTED to 5v. So you just sent how many volts into your Pi? 12? Excellent work. well done. Slow hand clap.
You decide to check the damage, hoping against hope that the Pi just kind of wouldn’t notice that you just rammed 12v up it’s tiny USB port and you can pretend like nothing happened. After all, no blue smoke came out, so … fine, right? Fine. Probably fine.
Except, no. Adjusting the voltage regulator to 5v (triple checked – bit late now, but whatevs) and trying to boot again does nothing. Well, not exactly *nothing*, but only some flickering of the activity light and no actual booting. Saddest of sad faces.
Alas Poor Pi
So that’s that then. You’ve fried your pi. It has gone toes up. Time to give it a viking funeral.
But. BUT. A bit of Googling seems to suggest a few things:
- There is such a thing as a polyfuse
- They can heal themselves when they’ve tripped.
- Actually flipping *HEAL THEMSELVES*
- The Pi has one on the USB power input.
So you leave it an hour and, with great hope in your dumb little heart, you plug it in.
Nothing. Just a bunch more flickering. Probing across the polyfuse seems to suggest that it’s maybe a bit better, but stil a loooong way away from being useful as part of a functioning computer. sigh.
M. Night Shyamalan style plot twist
Fast forward two weeks. You’ve nearly forgiven yourself for frying a perfectly innocent Pi. You’ve ordered a replacement and plumbed it in to your Bot, and you’re sitting at your desk idly surfing the web when you see out of the corner of your eye that poor little dead Pi, half hidden under a pile of papers. “I wonder…”, you, um, wonder.
So, you dig out a phone charger and a cable, and you plug it in. <DEITY> be praised! It’s booting. It lives! You’re like the Doctor freaking Frankenstein of consumer electronics! Except that he made a sort of patchwork quilt of chopped up people and you’ve reanimated a credit card sized computer. Same thing apart from that though. Probably.
Step aside Pi Zero, I give you Pi Zombie!
So, there you have it. You too can get away with stuffing 12v into a 5v hole, if you’re very , VERY lucky. But what have we learned? Well, we’ve learned:
- If someone gives you an adjustable voltage regulator and tells you that it’s set to 5v, don’t believe a damn word of it.
- Stick your multimeter across EVERYTHING.
- Raspberry Pis don’t like 12v up them, Corporal Jones.
- Polyfuses are an actual thing. They freaking HEAL THEMSELVES, people. Insane.
- Sometimes you can fall in the doodoo and come up smelling of Raspberries.