AVR-Chat

You might use a diode in series with the power input, Ryan, to protect 
from polarity inversion.  Better yet, use a bridge rectifier and you can 
use either polarity DC as well as AC input from a wall wart.  That way 
all you do is connect power...no problems with polarity or type as long 
as the voltage limits aren't exceeded.

For inputs, we use a 10K resistor in series with the input and depend on 
the internal diodes for clamping.  If speed isn't a factor, we might use 
2 resistors and a 0.1uf or a 0.01uf cap between them to common for a 
noise filter...which isn't a bad idea any time you can do it.

You can only go so far in making things idiot proof, you know.


REB



Ryan wrote:

>Thanks, I know exactly what you're talking about.  However, for
>someone who might inadvertantly connect a +12V supply to the pin... It
>would obviously try to sink lots of current through the diode, likely
>blowing it up, then blowing up the MCU.  Would the effectiveness be
>reduced by putting series resistors (say, 1k?) with the two diodes?
>
>Or if the supply was connected backwards, all the current would try to
>go through both diodes....  Trying to create an idiot proof box, but
>you know how that goes.  ;)
>
>Ryan
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>--- In AVR-Chat@yahoogroups.com, Ken Arck <ah6le@...> wrote:
>  
>
>>At 10:38 PM 7/8/2006 -0000, you wrote: 
>>
>>I need to protect an analog input for an AVR.  Protect it from ESD,
>>users connecting it wrong (i.e. to 12V power), etc.  Any suggestions
>>on what to use?  Unity gain opamp?  "transorb" or similar transient
>>device???  Discussion welcome.  Thanks,
>>
>><---Some expouse using zeners and currentl limiting resistors but I've
>>always found the leakage current to be an issue. So now I use regular
>>diodes to ground and the Vcc rail. See the attached schematic. The
>>    
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>diodes
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>>are general purpose silicon like 1N914 or 1N4148.
>>
>>Ken
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