The idea to get power from serial port is not so bad ... but you can only get it from Tx, RTS,... (Rx, CTS,... are receivers) and it doesn't give must current, but just put diods and you get constant positive voltage

1 - you speak with your mouth and listen with your ears !

2 - no matter if your batterypack delivers enough current for both ! and it will be empty faster.

3 - Usually, ground is used as a reference :
Tx and Rx are set to +U or -U (I found : 3V< U < 25V) compared to GND.

So you need 3 wires to connect 2 systems (without hard flux control) :
Tx1  <->  Rx2
Rx1  <->  Tx2
Gnd1 <-> Gnd2
more about serial port : sorry only french ;)

On Apr 5, 2005 9:26 PM, Marek Jawurek <> wrote:

Ok I am sorry for that stupid post about power over serial, I just
looked at the schematics of my gps receiver, now I see that there is no
VCC on the serial port so where should all the electrons move too ?

Anyway, I'd still like to connect the GPS to the serial port but I am
not that much into the electronics. Could you help me out with these:

1. The Tx line of the gps has to be connected to the Rx of the gumstix
and vice versa, right ?
2. The GPS needs power so connect it in parallel to the batteryback
which is running the gumstix. Any problem with that ?
3. What to do with the GND of the serial connector on the gumstix. What
is it needed for ?

4. Trying to check out the buildroot i encoutered these issues:

        As indicated in the WIKI I did:
svn co

in order to check out the buildroot. But all I got was :
svn: PROPFIND request failed on '/svn/gumstix-buildroot/trunk'
Could not open the requested SVN filesystem

Is it temporarily down ?

Thank you for your help.


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