[dorkbotpdx-blabber] ARRGGHH - Please check this circuit

[Ron Jackson]

Hans,

The problem is probably the transient that occurs when the LED's fire. 
With a fast scope and short ground connection you will probably see a 
short, maybe sub-microsecond, voltage drop that causes your 
microcontroller to lose it.

I think ATX supplies have a STANDBY+5 supply that is independent of the 
main 5 volt rail. I would try using that to power the microcontroller 
and associated logic and use the high current supply to drive the LEDs.

   -- Ron


> Hans Lindauer wrote:
>> Yes, R3 is really .56 ohms.  I'll try checking the rail voltage as I 
>> increase the PWM - that's a good idea.  I have a friend who's going to 
>> let me borrow a LabView DAQ so I can try to figure out better what's 
>> going on, but the DVM should give me some idea.
>>
>> One of the reasons I wanted to explore using 12V, was so that I could 
>> place a 7805 regulator between 12V and the logic portion of the board, 
>> with the idea that it would help to isolate it further while providing 
>> lots more overhead.
>>
>> It seems like the power sags more when I strobe the LEDs to full power 
>> than when I leave them on, so maybe the PSU has too slow of a 
>> response?  I can definitely see the Dorkboards' power LEDs go dim when 
>> the LEDs flash.  To address Mykle's concern, I am pretty much right at 
>> the upper limit of current draw for this PSU.
> 
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