>
> Hiya,
>
> I've set up two XBee pro units to do digital line passing - so the pin
> states are mirrored between the remote TX unit and the base RX unit..
>
> In setting up the units I had them on the same power supply and ground
> potential and had them working fine passing a %50 cycle 25Hz digital
> pulse (3.3v) between themselves - Well, the purpose of having wireless
> is so you don't have to use the same power and ground potential isn't
> it...
>
> So I set the RX unit up on its own battery power supply and sent it on
> its merry way to the other end of the desk all by its lonesome ... Now
> on the scope its giving a sine-ish wave output on its output pin (the
> mirrored one) at about 20Hz-ish when idle and when I send my 25Hz
> pulse its the same 20Hz-ish wave with little spikes where there should
> be a digital transition from high to low or vice-versa ...
>
> However ... this glitch disappears if I connect the units to the same
> ground potential.
>
> If I connect the two grounds by a 10MOhm resistor I get a kind of
> 'half-problem' where I get my digital pulse at 25Hz but modulated by
> the 20Hz-or-so pulse ...
>
>
> What am i doing wrong ? I have used the XBee's for line passing
> successfully beforehand - no idea where this glitch is coming from
>
> prob something really beginners ?
>
> nick
>
It's nearly impossible to help with something like this without being
able to actually see what is going on. But, it sounds like a scope
probe grounding issue to me.
The scope chassis and probe ground lead are connected to safety
ground. If you probe the signal without connecting the ground lead
you can get strange results. If you do connect the lead, you are
changing the ground reference for the device but that's the nature of
using a scope.
That you are getting spikes at the rising and falling edge of the
pulses makes me believe you are seeing the derivative of the pulse.
This occurs when you have a capacitor between the signal and the scope
input or when the scope is set to AC coupling. Not connecting the
probe ground can give the same results.
Richard
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/oopic/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/oopic/join
(Yahoo! ID required)
<*> To change settings via email:
mailto:oopic-digest@yahoogroups.com
mailto:oopic-fullfeatured@yahoogroups.com
<*> To unsubscribe from this group, send an email to:
oopic-unsubscribe@yahoogroups.com
<*> Your use of Yahoo! Groups is subject to:
No comments:
Post a Comment