AVR-Chat

On Mar 10, 2006, at 6:14 AM, Bryan Martin wrote:

> Well thats a yes and no.  I currently have a 12v wall wart going  
> into a
> NX1000 dev board.  From there I take 12v off the nx1000 and go to  
> the stk500
> dev board.  I also take 5V off the nx1000 and go to the VCC and  
> ground plane
> of the breadboard that holds the RF modules.

You have to look at the power supply input circuitry of both boards.  
I believe both have diode bridges between their power supply inputs  
and their regulators.

So the NX1000 "ground" signal becomes +0.6 or so volts on the STK500  
(because of 1 diode drop).

Which means that the +5V on the STK500 is at +5.6 or so with respect  
to the ground on the NX1000 (and your breadboard). Hence the funny  
readings.

You'd be better off, all things considered, to run the wall wart into  
a "Y" cable and then into both the NX1000 and the STK500. Then  
(assuming that their ground voltages are about the same) you can  
connect their ground planes together.

Of course, if the forward voltage drops on the input diodes are  
different (say if one uses regular 1N4001 diodes and the other uses  
Schottky diodes) you'll have all the power supply current going  
through one pair of diodes (the Schottky diodes, which have lower  
forward voltage drops).

Try to look at the power supply circuitry for both the NX1000 and the  
STK500 boards; I think you'll see that both have diode bridges.

I know the STK500 does; from the picture it looks like the NX1000  
does too.

> I think I will try to clean
> this up first in hopes that is the pblm.  I will try to drop the  
> NX1000 dev
> board all the way out of the picture first and hook the wall wart  
> direct to
> the SDK500 even though that will still be pushing 5.8v when taking  
> the pins
> high.  That would be controlled by the STK500 I think.
>
> Bryan
>
> ----- Original Message -----
> From: "Kathy Quinlan" <kat-yahoo@kaqelectronics.dyndns.org>
> To: <AVR-Chat@yahoogroups.com>
> Sent: Friday, March 10, 2006 9:07 AM
> Subject: Re: [AVR-Chat] RF communications
>
>
>> Bryan Martin wrote:
>>
>>> Thanks for your response.  I will check into the dropping the  
>>> from the
>>> STK
>>> but the pblm is not on the rails.  I am getting 4.9v as expected  
>>> from the
>>> 5v
>>> rail.  Problem is when I take a pin high on the 8515 it is  
>>> sending more
>>> than
>>> the 5v.  It is sending around 5.80v.
>>
>> IF THE +5V rail is 5V then the pins CAN NOT PUT OUT MORE THAN  
>> 5V !!!!!!!
>>
>> Are you feeding the same 5V to the RF Module ??
>>
>>
>> -- 
>> Regards,
>>
>> Kat.
>> ---------------------------------------------------------------
>>  K.A.Q. Electronics     Website: www.kaqelectronics.dyndns.org
>>  IM: Yahoo: PinkyDwaggy MSN: katinka@kaqelectronics.dyndns.org
>>  For Everything Electronics    Phone: 0419 923 731
>> ---------------------------------------------------------------
>>
>>
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