No blinking led, USB not found, hot to touch, what now?

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No blinking led, USB not found, hot to touch, what now?

(9 posts) (4 voices)

Started 2 years ago by amatic
Latest reply from amatic

amatic
Member

Hello,
I have a Maple r5 board. As the title says, since this morning when I plug in the board, the LED is not blinking, windows reports an unrecognized device, and the board seems to be getting hot (the processor).
Attached to the maple I had a motor driver shield with separate power lines (5V for driver chip, 12V for motors), common ground with the maple. Few pots were attached to maple's vcc and read by analog inputs. I had an arduino leonardo for serial communication connected to pins 7 and 8 which are 5V tollerant, and also common ground between arduino and maple. Maple was connected to the computer via USB.
Power jumper is set to "USB".

Everything worked just fine for a few days, but now the board won't boot up, even after disconnecting everything.

What can I do?

Posted 2 years ago #
hihohoho
Member

Try plugging a normal power supply in or 3.7Vbattery (disconnect from computer first). Leave it unplugged for a little while 'cos of the fuses that will reset after an hour.

Narrow down the possibilities. What were you doing to it before it died? 12V is a lot if it goes to the wrong place. I've killed a pic chip before by briefly touching stray wires, but modern boards are quite resilient. However, if the main processor is getting v.hot it's not a good sign. I presume nothing is connected to it now? Maybe measure the voltages going in to and out of the power ic. There are schematics available somewhere on this site.

Posted 2 years ago #
spas
Member

It sounds like the board has gone to that big landfill pit in the sky.

Posted 2 years ago #
amatic
Member

Thank you for the suggestions, hihohoho. The board is still unresponsive. I'm a noob, so I guess it's very likely I did something bad and damaged it, but I don't know what.

The only recent change I made is I had five 5k ohm potentiometers connected to vdda, gnd and respective AINs, I've changed two of them with 2.5kohm ones. I don't think there was a short anywhere since that setup worked for a few days.

As motor drivers, I'm using SN754410. They seem to have some kind of protection diodes, but there was noise on the pot readings when the motors were on. They probably affected ground levels or something. It worked for a long while, so I wasn't concerned about it.

The arduino is outputting 5V signals to pins 7 and 8. Are they really 5V tolerant for long periods of time? Last thing I did before I noticed the maple is unresponsive was to plug in the arduino into computer's usb, although, the maple could have died before.

Oh, maple was fun, so fast..

Posted 2 years ago #
hihohoho
Member

>> Oh, maple was fun, so fast..

I'm sorry for your loss.

As to 5V tolerance, I'm not sure it would matter. If you supply 5V to a 3V pin (usually) that pin will no longer function, but the rest will be fine (maybe). I've never tried it on a maple though. Maybe use a 3.3V zener diode+resistor to add a bit of protection (see basic 5v 3v level conversion in google). If you plugged your Ardunio into your PC while your maple was powered by another power source then that could potentially create problems, albeit briefly. Electricity is a pain sometimes. Literally. I would have thought the maple would have coped with that.

If you haven't already, add some diodes across the motors to protect the whole circuit. If a motor is running at high speed and you turn off power to your circuit the motor is freewheeling. It's now a generator. That's not good, especially if you suddenly stop the motor. See here for random google link http://www.thebox.myzen.co.uk/Workshop/Motors_1.html or here for wikipedia http://en.wikipedia.org/wiki/Flyback_diode.

Posted 2 years ago #
gbulmer
Moderator

amatic - "As motor drivers, I'm using SN754410. They seem to have some kind of protection diodes ..."

AFAIK, the 'protection diodes' on the SN754410 are for protection against Electrostatic Discharge (ESD), and not 'flyback protection diodes', which require much bigger current handling.

The SN754410 is very similar to the L293, which does not have 'flyback diodes'. The L293D does have internal 'flyback diodes'. I think you can just about discern the difference from Figure 3 in:
http://www.ti.com/lit/ds/slrs007b/slrs007b.pdf
which has external protection diodes, vs Figure 3 (L293D):
http://www.ti.com/lit/ds/slrs008c/slrs008c.pdf
which explicitly shows the L293D has internal protection diodes, whereas Figure 2 (L293) shows external protection diodes.

Ladyada's old (v1) Arduino motor shield uses L293D. She explains that she contacted TI about using the higher current SN754410:
"On using the SN754410: Some people use the SN754410 motor driver chip because it is pin-compatible, has output diodes and can provide 1A per motor, 2A peak. After careful reading of the datasheet and discussion with TI tech support and power engineers it appears that the output diodes were designed for ESD protection only and that using them as kickback-protection is a hack and not guaranteed for performance"
http://learn.adafruit.com/adafruit-motor-shield/power-requirements

(Full disclosure: I am not a member of LeafLabs staff.)

Posted 2 years ago #
amatic
Member

Thanks guys, I'll put on those protection flyback diodes. I hope that was indeed the problem and I will not fry the next board.

Will these do? http://www.diodes.com/datasheets/ds28002.pdf

or these: http://www.diodes.com/datasheets/ds23001.pdf

Posted 2 years ago #
hihohoho
Member

1N4001 would probably suffice. 50V 1A with a non-repeatable burst of upto 30A for 8.3ms, which should be more than adequate.

Posted 2 years ago #
amatic
Member

Ok. Thanks.

Posted 2 years ago #

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