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Possibly Dead Motor Shield
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Possibly Dead Motor Shield

by blrplt1 on Thu Aug 07, 2008 9:11 am

I hate for a first post to be for help, but I need some!

I was testing a gyro last night, on an Arduino with a working motor shield attached (with extended headers). The board was powered with a 12v wall wart, and the shield was powered via the Arduino.

I accidently shorted the 5v out with the 9v pin on the shield, heard electrical sparking, and immediately pulled the pin out. I noticed the power connection to the Arduino get quite hot, so I pulled the plug and let it cool off.

The Arduino survived, but the board does not seem to have any motor outputs at all now. The led lights up, so at least the power pin is still good. No caps are popped. and the board is still in perfect condition. What is most likely to have died first?

I have not yet been able to test the servo outs- I figure if they don't work, at least my driver chips are still good. Thanks for the help! I'm being much more careful with which pin is actually ground now...
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by adafruit on Thu Aug 07, 2008 12:11 pm

:( you could have popped the '595 or the 293Ds you can see if -any- motors work. if none do its probably the 595

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by blrplt1 on Thu Aug 07, 2008 3:09 pm

Thanks! I'll try to test it some more tonight, maybe send out for the 595. I'm still not sure exactly the mechanics of what happened, but hopefully it'll just be a matter of one replacement.
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by lou on Thu Aug 07, 2008 4:54 pm

blrplt1 wrote: I'm still not sure exactly the mechanics of what happened,


From your description, it sounds like you connected the 5V power supply to 9V. As the logic chips are only good up to 5-6v (depending on family), that could certainly kill them. You're just lucky AVRs are hardy beasties, or you'd probably be replacing that too.

I'd suspect the shift register may be what got whacked. The driver chips might have been able to withstand it, but it's not at all assured.
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by blrplt1 on Thu Aug 07, 2008 7:04 pm

More info, now that I have it in hand.

I get proper voltage from the Arduino power outs, but for whatever reason, the led does not light up when running off strictly USB power (arduino set to USB, jumper plugged into shield). I'm having trouble tracing the 5v in to the LED. What does that run through?
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by blrplt1 on Thu Aug 07, 2008 7:38 pm

Actually, I think I have traced the issue. It appears that the 5v Arduino supply is routed directly into both the L293's Vss inputs(duh.). The data sheet says those are logic level inputs.

However, led appears to be powered (when run with USB 5v only) through the Vs pin of the rightmost L293, when looking at the board with the resistor network on top.

Is this correct? The L293 data sheet defines the Vs pin to be the motor supply in. Not an EE, but it seems like voltage shouldn't be sourced from in input pin.

Anyways, either the L293's are both dead, or they need some special signal from the 595 that they're not getting. Think I'm just gonna replace all three. Whoops!
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