[sudo-discuss] Arduino current protection code?

[Anon195714]

Hi Tracy-

I was going to say the same thing but didn't want to risk making an ass
of myself in case there was some kind of magic software I didn't know about.

One possible way to protect against spikes is to use zener diodes across
the power input.  Let's say you want a maximum of 5 volts going into a
device.  OK, so get two zener diodes at anywhere between 5 to 6 volts,
and connect them "head to head" (facing each other) and connect the
"tails" across the power input to the device.  Anything over 5 volts
causes one or the other of the zeners to avalanche and conduct as a short. 

I would also have current-limiting resisters in series with both power
leads both before and after the zener diodes, because when the zeners
avalanche, they effectively become a short circuit, and that will cause
a current surge from the power supply.  But with resisters in series,
the resisters limit the maximum current draw, whether it's by the device
itself, or by the zener diode avalanching due to a spike. 

OK, so here's a crappy attempt to draw a schematic in ASCII.  Resisters
R1 limit current input when the zener diodes avalanche.  Resisters R2
limit the discharge of the capacitor C1 so it doesn't fry when the ZDs
avalanche.  C1 is an electrolytic capacitor to store a charge that
maintains power to the device during brief spikes when ZD has avalanched
and the power level toward R2 has decreased.

Power supply output + ----- R1 ------ R2 ------ device power input +
                                 |          |
                                 ZD         |
                                 |          C1
                                 ZD         |
                                 |          |
Power supply output - ----- R1 ------ R2 ------ device power input -


Calculate the value of resisters R based on the current level you need
to draw for the device, and the value of C1 based on the power needed by
the device during a momentary spike.

Hope this helps...

-George

 
======


On 13-02-25-Mon 9:28 AM, Deno Vichas wrote:
> tracy,
>
> you can't do it in software. by that time the micro controller already
> got the spike.  (i'm no hardware guru) but i believe you want to
> either put something a diode or resister on that input pin.  but it's
> hard to say without a schematic.
>
> - deno
>
>
> On 2/24/2013 7:18 PM, Tracy Jacobs wrote:
>> Hi all and Jake if you get this,
>>
>> Does anyone know the bit of code for protecting your arduino from
>> current spikes?  I could use that now.  I'm trying to run a bunch of
>> heavy duty servos with a bit of a load.  They have a separate power
>> supply, but I'm not using any motor controller.  Does this seem like
>> a bad idea?  Could that little code provide enough protection from
>> current spikes?
>>
>> Thanks for your advice,
>>
>> Tracy
>>
>> Thanks for your advice.
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