Splitting Serial

August · 10-31-2004, 09:38 PM

I need to provide GPS data to a laptop and an APRS tracker simultanously. I don't really want to have to buy a second GPS. Can serial be split into two serial connectors in parallel? Is there an interface on the market that can do this?

blurp · 10-31-2004, 11:26 PM

http://www.mp3car.com/vbulletin/show...t=serial+split

Come on, guys,

for 2 seconds before you post a question like this.

danon · 11-01-2004, 01:56 AM

wow, thx for the link!

.

August · 11-01-2004, 02:05 AM

Virtual com ports have nothing to do with my question. I don't need two software applications to access the GPS; I have two devices that need to access the GPS.

kingtut · 11-01-2004, 02:22 AM

you can't, you would risk blowing the 2 devices since each puts out current. Even if you would work around the current issue, one device would confuse the other since one might send a specific request to the GPS that the other did not expect. Serial is a protocol between 2 devices, that is the short answer.

zPilott · 11-01-2004, 02:24 AM

does the gps receive data from the PC, or is it only one way? If the gps is expecting config data from the PC, I think you might have trouble if both are trying to send something out.

If the gps is sending only you might be able to try something like this:
http://www.airborn.com.au/rs232.html#monitor

zPilott · 11-01-2004, 02:29 AM

another option might be to run a null modem cable from the first pc to the second, and somehow propagate the data across, so that the second device would think it is connected to the gps, not to a pc.

August · 11-01-2004, 04:14 AM

I found this in a PDF manual for a Ratheon GPS.

Quote:

When using the NMEA 0183 format, the Raystar 112 can provide data
for at 2 or more navigation equipments when connected in parallel. Be
sure that all devices connected to the data output ( plotters, video
sounders, radars) are programmed to use the NMEA 0183 data format.

WARNING: Do NOT GROUND the Data, Data return lines, or the
Shield of the interface cable at any of the external navigation
equipments.

The ability to do this must be part of the NMEA standard. Any thoughts?

Laidback · 11-01-2004, 04:19 AM

If you're just reading there's no problem.

Ricky327 · 11-01-2004, 12:12 PM

Quote: Originally Posted by August

Virtual com ports have nothing to do with my question. I don't need two software applications to access the GPS; I have two devices that need to access the GPS.

I though as much but relax man.

Heres your solution :

GPS <---> PC ( Normal 2 way using RX/TX, can read and write to GPS )
:
: -------> Another device (1 way using the TX line of the GPS, device can only read)

Dont forget the GND for both PC and other device.

Ricky327 · 11-01-2004, 12:19 PM

Quote: Originally Posted by August

Is there an interface on the market that can do this?

Dont think so, but you can try to solder 2 wires that connect to the TX and GND of the serial connection of the GPS...and connect this to the "READ ONLY" device.

If this doesnt work properly due to the TX line being loaded with 2 devices then you may need to add a MAX232 chip to boost the signals and split them to 2.

blurp · 11-01-2004, 05:58 PM

Quote: Originally Posted by August

Virtual com ports have nothing to do with my question. I don't need two software applications to access the GPS; I have two devices that need to access the GPS.

Read post 14 on the thread I linked to above. And I stand by my original comment.

!!!!

zPilott · 11-01-2004, 07:31 PM

Quote: Originally Posted by Ricky327

If this doesnt work properly due to the TX line being loaded with 2 devices then you may need to add a MAX232 chip to boost the signals and split them to 2.

The max232 is for converting 5V TTL (1 is +5V, 0 is 0V) to the voltages for rs232 (1 is -15V, 0 is +15V), its not gonna help with this problem

Ricky327 · 11-01-2004, 07:38 PM

No I meant...

GPS ----> RS232 > TTL > RS232 > PC
:
:--------> RS232 > TTL > RS232 > Other device

The MAX232 contains 4 converters, and can be wired up to buffer the signal from the GPS before feeding them directly to the 2 devices.

It converts the RS232 down to TTL and then to RS232 again

If that can help I dont know, but its just a mean of buffering the signals before sharing ONE signal by the 2 devices.