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Data is inverted when compared to the standard output from a Garmin GPS12 or TomTom wired receiver.
Is the Tom Tom receiver not RS232 levels then?
I'd thought it was, from the data I've found scattered around. I'm interested in this as I want to connect the Inforad to a Tom Tom cradle for a Dell X30 and had thought the Tom Tom cradle accepted RS232 levels?
Joined: Jan 14, 2005 Posts: 19638 Location: Blackpool , Lancs
Posted: Sat Jul 09, 2005 11:40 am Post subject:
Try one of these if you want "true rs232" - extact below is from Garmin site I have one on the Volvo's roof it works great - Mike
"GPS35-HVS Attached 5 meter power/data cable with bare wire ends. Accepts power from unregulated high voltage power supplies between 6 and 40 VDC. Asynchronous serial data interfaces via 2 serial ports with true RS-232 voltage level outputs."
All I can say is when I looked at the outputs of the Garmin GPS 12 and a tomTom wired on a scope, they both had similar outputs. Logic 0 is at 0V and Logic High is at approx 3.3V. Neither showed the normal RS232 +/- voltage swing which you would expect from true RS232. What I don't know is if the Ipaq expects a standard RS232 at its input, or if when you connect to a true serial port as on a PC, what you get out, I haven't looked so I can't say.
When I configure TomTom 3 or 5 for a wired input the Garmin and the TomTom both work if you use a standard wired receiver selection at 4800 baud.
Just to add confusion, and I really have no idea why this happens, TomTom 5 will not run reliably with a non TomTom receiver except the Inforad with the data inversion I have descibed. Levels / later version of NMEA / slew rates? I have no idea.
All I can say is it runs well with the simple circiut I used on an Ipaq 2210. Other PDAs may be more selective and need true RS232, I only have the Ipaq so I can't say.
I have also connected the Garmin GPS 12 to the Ipaq with tomtom. I got the Garmin 4/5 pin connector from the PFranc web site, for the price of a donation!
Modified a standard Ipaq connector and using a HP car adaptor for the Ipaq ran the Ipaq and the Garmin off the same supply. I had the connector and supply any way but I think they cost approx £18, and so I didn't need to buy the Garmin cable. I just fed the GPS 12 output straight into the Ipaq.
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All I can say is when I looked at the outputs of the Garmin GPS 12 and a tomTom wired on a scope, they both had similar outputs. Logic 0 is at 0V and Logic High is at approx 3.3V. Neither showed the normal RS232 +/- voltage swing which you would expect from true RS232. What I don't know is if the Ipaq expects a standard RS232 at its input, or if when you connect to a true serial port as on a PC, what you get out, I haven't looked so I can't say.
