Problems with a Revison D board

Problems uploading, serial connections, BUBs, P4, FTDI cables, etc
Post Reply
Bitrex
Posts: 3
Joined: Mon Feb 15, 2010 5:42 am

Problems with a Revison D board

Post by Bitrex » Mon Feb 15, 2010 6:04 am

Hey all, I have a Revision D BBB, and I'm having some trouble. Recently I've started using a powered prototype board, and I thought by setting the jumper to "External" on the board I would be OK connecting the TTL-USB cable and powering the board from the powered breadboard at the same time. However, in working on my circuit I've noticed that even with the cable removed and no connections made to the Arudino's +5V connections, the power LED will turn on when I connect a pullup resistor to an input with a normally open switch to ground. This seems to happen on all of the pins...I don't think that this is intended behavior. The issue that caused me to notice this is that soon after setting up the powered prototype board and connecting the TTL-USB cable, the TTL-USB cable failed (no longer produces an output voltage). I'm wondering if somehow the two symptoms could be related. Anyone have any ideas one what could be going wrong?

floresta
Posts: 93
Joined: Mon Jul 28, 2008 6:52 pm
Location: Western New York, USA
Contact:

Re: Problems with a Revison D board

Post by floresta » Mon Feb 15, 2010 9:10 am

Bitrex:
...the power LED will turn on when I connect a pullup resistor to an input with a normally open switch to ground.
Do you mean that (1) The Breadboard power rail bus pins (V+ and GND on the side of the BBB) are not connected to the powered breadboard and (2) the pull-up resistor is connected to +5v?

If that is the case you are feeding +5v through the pull-up resistor into an output pin of an unpowered IC. This is never a good idea.

Don

Bitrex
Posts: 3
Joined: Mon Feb 15, 2010 5:42 am

Re: Problems with a Revison D board

Post by Bitrex » Mon Feb 15, 2010 7:49 pm

Thank you for your reply. Yes, apparently that was what I was doing, applying power to the inputs of an unpowered Arduino. I've some more experimenting and the troubles started because the power input connections on one side of my board turned out to be intermittent - I must have made some bad solder joints somewhere. So when I removed the pullup, the "power" would turn on and off, since it wasn't getting any power to begin with. It worked normally for a time because I also had a connection made to the +5V pin on the row of headers which was also connected to the supply, but when that was removed...

In any case, maybe if I'm lucky the microcontroller wasn't destroyed. I don't have any code on it, so I'll have to wait until I can get a new serial cable to find out. In the meantime I'll try to find the reason why that set of power connections wasn't working properly.

paul
Site Admin
Posts: 735
Joined: Mon May 12, 2008 4:19 pm

Re: Problems with a Revison D board

Post by paul » Tue Feb 23, 2010 12:28 am

To expand on what Don said - power applied to pins of a microcontroller that is off will flow through the protection diodes of the microcontroller, often causing the microcontroller function (although erratically) and power other circuits. Usually no harm is done - I guess depending on what else is connected. One would worry about this though, if for example the microcontroller was hooked up to some H-bridge powering some heavy duty equipment - that might have power applied to it. Then all of a sudden things start moving that were supposed to be off.

A similar problem caused the Arduino NG not to boot because a chip was getting enough power from an input line to put out noise on an output line

pb

paul
Site Admin
Posts: 735
Joined: Mon May 12, 2008 4:19 pm

Re: Problems with a Revison D board

Post by paul » Tue Feb 23, 2010 12:28 am

To expand on what Don said - power applied to pins of a microcontroller that is off will flow through the protection diodes of the microcontroller, often causing the microcontroller function (although erratically) and power other circuits. Usually no harm is done - I guess depending on what else is connected. One would worry about this though, if for example the microcontroller was hooked up to some H-bridge powering some heavy duty equipment - that might have power applied to it. Then all of a sudden things start moving that were supposed to be off.

A similar problem caused the Arduino NG not to boot because a chip was getting enough power from an input line to put out noise on an output line

pb

Post Reply