Geek help needed: RS232 to USB adaptor

Amulet

Amulet

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I would expect to be able to use this cable:
http://www.amazon.co.uk/dp/B0000ADX9D/ref=pe_385721_37038051_TE_dp_1
connected to this device:
https://www.olimex.com/Products/Components/Cables/USB-Serial-Cable/USB-Serial-Cable-F/
to take serial output from a Garmin GPS72 to a USB input on my computer and create a virtual COM port for nav software expecting RS232 input.
It does not work in my hands. I have tried it on a Windows 7 and a Windows 8 machine. Both insist that my driver is up to date. Both succeed in creating the virtual port.
The Windows 8 machine tells me "Device cannot start" "non-existent device". The windows 7 machine tells me everything is working perfectly, but none of my nav packages can use the output from it.
I have examined the raw output using PUTTY. It sure as hell isn't NMEA. It looks like gibberish. I have tried switching baud rates to no avail. I have used this setup before with adapters from different manfacturers, and can make it work with exactly the same computer and GPS through an adaptor from FTDI Chip.

I am on the verge of giving up and buying an adaptor of a type I have used before, but I am frustrated that I can't work out what is wrong.
 
elton said:
USB is serial, but it's not serial as in RS232. It's a different thing. They have different names because they are different.
Click to expand...

That is a USB-serial adapter though, just with a different end.

Quite correct that the set up should work. Has the baud been changed to 4800? Has the Garmin device been set to NMEA output? Garmin do have different modes. Has the Garmin been grounded to power negative rather than just to the gnd of the serial? Garmin often need this.

Have you verified the Garmin some other way? I have a Garmin handheld that outputs gibberish because it's broken rather than because my setup doesn't work - I have separately verified the setup elsewhere :)
 
'
lustyd said:
That is a USB-serial adapter though, just with a different end.

Quite correct that the set up should work. Has the baud been changed to 4800? Has the Garmin device been set to NMEA output? Garmin do have different modes. Has the Garmin been grounded to power negative rather than just to the gnd of the serial? Garmin often need this.

Have you verified the Garmin some other way? I have a Garmin handheld that outputs gibberish because it's broken rather than because my setup doesn't work - I have separately verified the setup elsewhere :)
Click to expand...

+1, sounds like the Garmin output needs to be set up correctly to NMEA.

Yoda
 
Thanks for the input. Yes it is an adaptor. That's its job. I can take it out and replace it with one from another manufacturer and everything works. I expect it to be 4800 baud but have tried all other speeds as well. It says in tech spec that its default is 115200 which I have tried. I am wondering if it is pumping data at a speed too fast for the rest of the setup. I have also tried setting everything to the Garmin protocol rather than NMEA, and again I can make it work with the old device but not the new one.
 
lustyd said:
That is a USB-serial adapter though, just with a different end.

Quite correct that the set up should work. Has the baud been changed to 4800? Has the Garmin device been set to NMEA output? Garmin do have different modes. Has the Garmin been grounded to power negative rather than just to the gnd of the serial? Garmin often need this.

Have you verified the Garmin some other way? I have a Garmin handheld that outputs gibberish because it's broken rather than because my setup doesn't work - I have separately verified the setup elsewhere :)
Click to expand...
Ok, I didn't read the second link. My apologies to the op :o
 
Your USB converter is giving 3.3 V outputs. This is Serial TTL levels and lower than pure serial Voltages. Sometimes one gets away with this however you might need a level converter as discussed on another forum Or find a USB adaptor that puts out Serial voltages which I believe are about 5 V.

Find a nerd who understands Commodore 64 computers and you might find a level converter:)

Quote

NOTE: RevB is completely different hardware, based on Ralink RT3050 SoC. The serial port runs at 57600 baud, 8 bits, no parity, 1 stop bit using ANSI terminal emulation. Levels are not RS232 voltage levels, but +3.3V TTL logic. Use an interface converter chip (Max232/Max3232/DS275 etc.) to connect to standard RS-232.

End Quote

http://en.wikipedia.org/wiki/MAX232
 
Amulet said:
Thanks for the input. Yes it is an adaptor. That's its job. I can take it out and replace it with one from another manufacturer and everything works. I expect it to be 4800 baud but have tried all other speeds as well. It says in tech spec that its default is 115200 which I have tried. I am wondering if it is pumping data at a speed too fast for the rest of the setup. I have also tried setting everything to the Garmin protocol rather than NMEA, and again I can make it work with the old device but not the new one.
Click to expand...

In that case sounds like you may have a duff unit to me if another serial converter works.
 
lustyd said:
In that case sounds like you may have a duff unit to me if another serial converter works.
Click to expand...
This is a classic example of some USB to Serial adapters work with some kit and not others. My Morningstar MPPT controller would only work with the adapter they recommended.
 
Haven't played with these things for a year, but last time I did, I seem to recall needing to invert the data, as in 0>1 and 1>0, before terraterm would read a ublox gps via a usb/rs232 adaptor?
I used a transistor, which also gave 5V logic levels.
 
Thx everyone for the input. Sorry for the delay - been on the water for the last three days, which beats fighting with electronics. I'll faff around a bit more and then capitulate and buy one that I know works. Because I've made this setup work with diverse suppliers I assumed it'd be easy and ordered two of these on the basis of price. (Long story why..) Can't decide whether to solder the second one in to see if it works. Somehow doubt it.
 
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