Author Topic: Shorting sensors cause Axon reset?  (Read 594 times)

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Offline mstachoTopic starter

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Shorting sensors cause Axon reset?
« on: July 31, 2012, 07:27:01 AM »
I'm not convinced that this is the case, but it seems to be.  I have variable resistors attached through voltage dividers to my ADCs on the Axon.  Input is 5V from the 5V regulated line on the Axon.  I seem to keep resetting the Axon whenever the resistors go too low. 

My voltage divider has 10K resistors on the grounded end, so this doesn't really make sense to me.  However, I should mention that I've already blown up an Arduino's USB doing this...somehow, although I'm not at all sure how since it was on external power at the time :-P

So, does this sound like its my sensors, or something else?

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline Gertlex

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Re: Shorting sensors cause Axon reset?
« Reply #1 on: July 31, 2012, 11:29:11 AM »
You neglect to mention what sensors are you using? :)

Sharp IR sensors definitely have this problem (and its solvable). Example thread.
I

Offline mstachoTopic starter

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Re: Shorting sensors cause Axon reset?
« Reply #2 on: July 31, 2012, 11:36:27 AM »
They're these:  http://www.robotshop.com/ca/interlink-05-circular-fsr.html

What I don't understand is: if they are shorting, but the supply voltage is 5V, and we're reading through a voltage divider, shouldn't the ADC just get 5V dumped into it, and no problems happen?  It has a massive input impedence, so putting 5V directly into it, even with the shorting, shouldn't cause a reset...and the 10K pulldowns are supposed to limit the current to something small...

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline Soeren

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Re: Shorting sensors cause Axon reset?
« Reply #3 on: August 01, 2012, 12:09:48 PM »
Hi,

They're these:  http://www.robotshop.com/ca/interlink-05-circular-fsr.html

What I don't understand is: if they are shorting, but the supply voltage is 5V, and we're reading through a voltage divider, shouldn't the ADC just get 5V dumped into it, and no problems happen?  It has a massive input impedence, so putting 5V directly into it, even with the shorting, shouldn't cause a reset...and the 10K pulldowns are supposed to limit the current to something small...

A/D-C input impedance isn't necessarily as high as you may think, but anyway... Any voltage between VDD and VSS through a 10k resistor should not cause any reset, as the max. current will be too low to cause a brownout on the supply (unless perhapsit's riding on the verge already).

If it happens any time the A/D-C sees close to VDD I'd check the code to see if it could be a sw problem - rig up with a potentiometer replacing the FSR and a voltmeter (VSS to A/D-C input)  to see if you can reproduce the reset condition at will and at what voltage.
If you can, check with a simple A/D-C code made from scratch (i.e. not by cut'n'paste from your existing program). If it still resets repetedly, you may have damaged the controller or perhaps just the particular input (=> test with another input then).
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline mstachoTopic starter

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Re: Shorting sensors cause Axon reset?
« Reply #4 on: August 01, 2012, 12:19:13 PM »
Yeah, I've just about given up on this.  For some reason, perhaps it's a combination of frying the Axon and killing my PC, I just can't get ADCs working anymore :-P

I've  moved over to my ARM development board for good now, and it's going well, so I think I definitely fried the Axon.  Oops...

MIKE
Current project: tactile sensing systems for multifingered robot hands

Offline Admin

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Re: Shorting sensors cause Axon reset?
« Reply #5 on: August 10, 2012, 07:48:04 AM »
Post the circuit diagram you used for it . . .

But to fry the Axon, you'll have to do much more than use this sensor. I suspect you're doing something else wrong, too, lol . . .

It could be your code, a dead battery, or a short in another circuit.

 


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