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Semi-failed "blink" test - overenthusiastic output voltage

Posted: Sat Oct 24, 2009 5:29 pm
by ThomM
Hello there,

I've put together my first BBB (a hand-me-down RevD2 from a friend) and everything is working... mostly. It powers on fine, and all the voltages are fine (~4.8 at all the places the instructions say to test). However, when I uploaded the Blink sketch to test it out, the LED on pin 13 blinks when it's supposed to be on. "That's weird" I thought, so I set the sketch to simply switch the LED on, and it still blinks. I broke out the multimeter and the voltage going through the LED is all over the shop, from ~2.7 up to ~6.8 volts and everywhere in between. It does hit 4.8 specifically occasionally, but varies wildly.

Now, I'm a total beginner with this stuff and don't really know where to go from here. There don't appear to be any problems with communicating with the chip or with connectivity at the board but obviously something is going wrong somewhere. Some of my solder joints aren't the prettiest but they're all generally "good" (shiny etc). I'm a soldering newbie too, is it possible I've overheated one of the components or something? My rudimentary understanding suggests that if all the voltages are ok at the power buses then it's probably not a faulty component, but what do I know :)

So, err, what do I do now to try and work out what's wrong? I'm not sure if this is even the best place to ask, but I don't know where else to go really, so any advice would be very much appreciated.


-Thom M

Re: Semi-failed "blink" test - overenthusiastic output voltage

Posted: Sat Oct 24, 2009 6:17 pm
by paul

I'm a little confused by your description of the blink. Is it random? Is the LED fading in and out. Does it seem glitchy (random) or regular? What does the IDE say after uploading? Confirm your meter settings - you shouldn't be getting 6.8V out of anything on a board powered by 5 volts. Do you have external, higher voltage power supply hooked up to the five volt pins?

Confirm that the pin as been set to OUTPUT with a call to "pinMode" function.

Try these things:

Switch to another pin and report what the results are. How are you powering the board?
Check power connections on the board, and with the cable.
Confirm that chip is firmly seated in the socket.
Check continuity between the BBB pin and the atmega pin on the chip.
It's probably not toasted components, but could be a flaky soldering joint, on the LED pin or the chip power pin.


Re: Semi-failed "blink" test - overenthusiastic output voltage

Posted: Sat Oct 24, 2009 11:44 pm
by ThomM
Hi Paul.

Thanks a million for your fast and comprehensive reply!

Turns out my BBB system was suffering from a major case of user error...

The LED I was testing it with was a blinking LED :oops: :cry:

All is well now, and I am super-happy. Sorry to trouble you with this non-issue, but thanks again for your advice - it certainly helped to narrow down the "problem"! I'm using a digital multimeter and I think it must have been changing units to millivolts or something when it was reading 6.8, I'm new to using that too...

Look forward to buying a 4-pack of these soon :) I definitely like the form-factor and they're certainly more economical than the other options.

Thanks again for your reply!

-Thom M