Had two SainSmart relay boards (one w/8 relays, one with 16) all jumpered-up to the GPIO, thought I had it right. Powered up, both red & green LEDs on the Pi lit up solid. Nothing happening that I could tell, otherwise. Tried to PuTTY in, and no connection could be made.
Unplugged the 5v mini-USB power (was using the one that came with the Pi), plugged it back in. Same thing, both lights on.
Third time I plugged it in, all relays on the 8-relay board lit up at the same time. They turn on when the GPIO pin drops below 3.3 v, iirc.
I knew that wasn't a good sign so I immediately unplugged.
Never saw any smoke, but the voltage regulator chip(s) near the usb seemed a bit warm.
Next time I tried to power up, no lights would come on on the pi. It's been that way ever since.
Worth noting: The 16 relay card uses 12 v. for the coils, and when you put 12 volts into the board, it does provide 5 volts for logic. There's a 5 v pin on the relay board.
If 5 v is connected to the pi board from the relay board, the relays that are connected to the GPIO just stay turned on. I saw someone had posted a discovery, that if you jumper the 3.3v pin on the Pi to the 5v pin on the relay board, it then works fine.
I tried it (before this issue) and I was able to have the relays turn on and off. This was before I jumpered all the GPIOs to all the relay inputs on both boards, though.
After the no-lights-on on the pi last night, I gave up. I saw somewhere that some of the fuses are the kind that will reset "after a day or two" so I hold some hope... but I know if you put too much voltage to an GPIO pin, you can brick it because the fuses are not where they can protect anything that way.
I had a buddy track it out this morning at my shop, and all transistors and components he could check (including FB1 through FB 6 or whatever) all checked okay.
There's no obvious burns on any traces, so we're a little mystified.
I know one for-sure fix: A new pi. (I've ordered one.) But I don't want to wind up in the same boat with the new one.
I guess I'll go with the 1K resistor between the pi's GPIO and the relay board for the 16 relay board. I just wish the 16 relay board was set up like the 8 relay board. The 8 relay board works great, right out of the box. I could buy two more, but heck, they're almost only a couple of bucks less than the 16 relay board so I'd be out twice the money.
Thanks for reading all this! Looking forward to your input/feedback.