AVR-Chat

Thanks for the explination Kat.  I am learning as I go so please excuse the 
newbee question but I learned something new.

Thanks again,

Bryan

----- Original Message ----- 
From: "Kathy Quinlan" <kat-yahoo@kaqelectronics.dyndns.org>
To: <AVR-Chat@yahoogroups.com>
Sent: Friday, March 10, 2006 8:37 PM
Subject: Re: [AVR-Chat] RF communications


> Bryan Martin wrote:
>
>> That was it.  When I sourced VCC and ground off the SDK500 the voltage 
>> went
>> to 4.95 w/no resistors.  Question though while were are talking about 
>> this.
>> Lets say I wanted to run two different power supplies one for part of the
>> controller portion and another for the RF portion (picture 2 different
>> battery banks - trying to isolate noise getting into the RF side) is this
>> possible?  Would this work if I connected the ground planes together?
>
> OK do you know much about electronics ?
>
> If yes then you realise you need a common reference point or your signals 
> will
> appear to float and you will get various problems.
>
> If no, then here is the explanation:
>
> If you have 2 batteries say 1.5V and 9V, if you measure from the positive 
> of
> the 1.5V to the negative of the 1.5V you well get a voltage of 1.5V. The 
> same
> with the 9V battery, measure from the + and - terminals and you will get 
> 9V.
>
> Now if you measure from the 1.5V's - terminal to the 9V + terminal, you 
> will
> see no voltage (in the real world the multimeter will show some stray 
> voltage,
> but this would only be a few milli volts) you will not measure 9V. The 
> reason
> is the current has no where to go to return to the - terminal of the 9V 
> battery.
>
> So if we place a wire between the -terminal of the 1.5V and 9V batteries, 
> and
> then measure between this wire and the + of either battery, we will see 
> 1.5V
> at the + terminal of the 1.5V battery and 9V at the + terminal of the 9V 
> battery.
>
> So why did you measure 5.8V in your RF module:
>
> Well there are 2 main reasons:
>
> #1 the module was being feed from more than +5V
>
> #2 the length of wire between the 0V rails on the different boards 
> (possibly
> through resistors, diodes etc) was sufficient to raise the 0V rail of the 
> RF
> module to 0.8V
>
> I hope this helps.
>
> -- 
> Regards,
>
> Kat.
> ---------------------------------------------------------------
>  K.A.Q. Electronics     Website: www.kaqelectronics.dyndns.org
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