Author Topic: Arduino pro mini - program failure at 9V  (Read 3235 times)

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Offline mtdoc

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Arduino pro mini - program failure at 9V
« on: October 26, 2015, 06:19:37 am »
So I'm putting together a Star Wars Jawa costume for one of my sons for  Halloween.   I decided to jazz it up with some LEDs and for the sake of speed and simplicity resorted to using one of these Pro Minis - doing a slight modification of the stock "Knight Rider 3" sketch - just adding a momentary switch to be able to turn on the effect.

For some reason the sketch will not run when the supply voltage is greater than about 8 volts.  I plan on powering it with a 9V battery.  The problem was easily solved with a voltage divider but I don't understand why it wouldn't work with 9V.  I've powered several Pro Mini projects with 9v in the past without issue.

I'm sure there's a simple explanation that my amateur brain is missing. Thanks to anyone who can enlighten me.
 

Offline dadler

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Re: Arduino pro mini - program failure at 9V
« Reply #1 on: October 26, 2015, 06:27:50 am »
How much current is your circuit pulling?
 

Offline miceuz

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Re: Arduino pro mini - program failure at 9V
« Reply #2 on: October 26, 2015, 06:30:36 am »
Check the voltage on the output of the regulator. Usually regulators on those boards are swept from a factory floor somewhere and don't meet specs at all. As a workaround, get yourself a dc - dc buck module from the same source and power the Arduino board via it to 5V directly.

Offline mtdoc

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Re: Arduino pro mini - program failure at 9V
« Reply #3 on: October 26, 2015, 06:31:53 am »
How much current is your circuit pulling?

20-30mA
 

Offline mtdoc

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Re: Arduino pro mini - program failure at 9V
« Reply #4 on: October 26, 2015, 06:37:51 am »
Check the voltage on the output of the regulator. Usually regulators on those boards are swept from a factory floor somewhere and don't meet specs at all. As a workaround, get yourself a dc - dc buck module from the same source and power the Arduino board via it to 5V directly.

That's a good point.  I should have thought to check that - it didn't occur to me that a faulty regulator would cause that kind of failure (though it should have ::).  I'll look at that the next time I fire it up.

I solved the issue with a voltage divider dropping the battery voltage to 7.5V or so.  It only has to work for a few hours on Halloween....
« Last Edit: October 26, 2015, 06:52:44 am by mtdoc »
 

Offline LabSpokane

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Re: Arduino pro mini - program failure at 9V
« Reply #5 on: October 26, 2015, 09:21:32 am »
Have any 78XX series voltage regulators lying around? 
 

Offline miceuz

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Re: Arduino pro mini - program failure at 9V
« Reply #6 on: October 26, 2015, 09:52:26 pm »
I solved the issue with a voltage divider dropping the battery voltage to 7.5V or so.  It only has to work for a few hours on Halloween....

Voltage divider is a pretty lame solution - it's either very high impedance (can not provide enough current) or very wasteful. Just use an LM7805 and power arduino directly to 5V pin.

BTW, how are you switching LEDs? Sourcing current from Arduino pin?

Offline obiwanjacobi

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Re: Arduino pro mini - program failure at 9V
« Reply #7 on: October 26, 2015, 10:30:01 pm »
You are powering it on the RAW pin, right....

(just checking)

Offline mtdoc

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Re: Arduino pro mini - program failure at 9V
« Reply #8 on: October 27, 2015, 03:49:41 am »

Voltage divider is a pretty lame solution - it's either very high impedance (can not provide enough current) or very wasteful. Just use an LM7805 and power arduino directly to 5V pin.

I agree - it's not the optimal solution.  But the whole idea of this was just a very small, quick solution to fit in a very small form factor - to be strapped to a 9 yr old's arm for a few hours of trick or treating.  I've got a whole bin of voltage regulators but using one would mean a bigger form factor.

Quote
BTW, how are you switching LEDs? Sourcing current from Arduino pin?

Yep - see the "knight rider" link in my first post.

This is not intended to be a finely engineered project - just something I put together in an hour one evening.

Thanks for everyone's ideas.
 

Offline mtdoc

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Re: Arduino pro mini - program failure at 9V
« Reply #9 on: October 27, 2015, 03:50:59 am »
You are powering it on the RAW pin, right....

(just checking)

Yep. Thanks.
 

Online Seekonk

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Re: Arduino pro mini - program failure at 9V
« Reply #10 on: October 27, 2015, 05:12:12 am »
Nice to know it will still work to that voltage and not explode.  I was given an item with a 3.3V micro in it that didn't work.  I powered it up to 12 volts and did some testing.  The 3.3 regulator was supplying 11V to the micro.  Replaced the regulator and it has worked fine ever since.  Never thought that was possible for a 3.3V device to survive that much voltage.
 

Offline LabSpokane

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Re: Arduino pro mini - program failure at 9V
« Reply #11 on: October 27, 2015, 05:23:21 am »
Mtdoc

If you need it, I can send you an APM out of my stash. It would likely make it there before the end of the week.
 

Offline mtdoc

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Re: Arduino pro mini - program failure at 9V
« Reply #12 on: October 27, 2015, 05:29:34 am »
Mtdoc

If you need it, I can send you an APM out of my stash. It would likely make it there before the end of the week.

Thanks for the offer. I actually have a stash of them.  This one is actually working fine with my current bodge solution - so I haven't been bothered to change it out.
 

Offline Wilksey

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Re: Arduino pro mini - program failure at 9V
« Reply #13 on: October 27, 2015, 05:38:43 am »
Does the micro power up or does the regulator go into "over voltage protection" mode?
 


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