Thread: Earthmate USB to Serial cable

Rando, can you post the pic? I want to see what I can do to make mine as serial.
Thanks

Sorry, the digicam is out of town with the lady. No matter, it's simple enough you don't really need a picture.

Just snap off the cover on the GPS end of the GPS<->USB cable that came with the Earthmate. You will see all 12 pins in there. Look at the existing wires and match them up to the pin numbering scheme below. The existing USB connections are in bold.

Delorme Earthmate II GPS - Pinout
----------------------------------
1 - GND
2 - USB Data+
3 - USB Data-
4 - +5V
5 - RS232 RXD
6 - RS232 TXD
7 - RS232 DTR
8 - +5v
9 - GND
10 -
11 -
12 - SHIELD

Here is the pin-out for a DB9 serial connector.

RS232 DB9 - Pinout
------------------------------------
1 DCD Data Carrier Detect — Input status Line
2 RxD Receive Data — Receives bytes into PC
3 TxD Transmit Data — Transmits bytes out of PC
4 DTR Data Terminal Ready — Output status line
5 SG Signal Ground
6 DSR Data Set Ready — Input status line
7 RTS Request To Send — Output status line
8 CTS Clear To Send — Input status line
9 RI Ring Indicator — Input status line

Solder the GPS TxD line (pin 6) to the DB9 RxD line (pin 2); the GPS RxD line (pin 5) to the DB9 TxD line (pin 3); the GPS pin 7 to the DB9 DTR line (pin 4); GPS GND (pin 1 or 9) to DB9 SG line (pin 5).

Next you need to supply a 5v source to GPS pins 4 or 8 (your choice). The simple thing to do here is just use the USB cable for power. To avoid confusion, you might want to lift the USB Data+/- pins in that case or make a USB power passthrough cable that only passes the +5V and GND signals but not Data+/-. Alternatively you could attach a standard PC molex connector.

That's it. As soon as the device gets power it will start to pump out an NMEA stream 4800/8/n/1. I believe the device will go into sleep mode if DTR goes low. By default, your PC will assert DTR high anytime the COM port is opened so (in general) you don't really need to worry about it.

If you still need pics, I should be able to take some next week.

Originally Posted by asci01

Any luck with the pictures, please?

Ha! I completely forgot. I'll try to put some up tonight.

Originally Posted by Supermike

(just depends on how you look at the connector - but should be obvious once the USB pins are identified (since they are the only ones hooked up).

I pulled the 5volts off the USB as you suggested.

Yep, that's why I didn't bother explaining which side is which or even rush to post a picture. There is NO CHANCE to mix it up since the existing wire configuration completes the explanation. In any case, here is a pic. The oem USB wires are on the right side. The serial wires I added are the ones in the middle/left. Sorry the picture is so blurry. I guess I need to read up on macro mode on the digicam.

Also, you really should thank the original poster as well as a few others (posted elsewhere on the web) that I 'borrowed' this info from. My only contribution, if any, was clarification.

Umm ... yep ... I think flexible 'stranded' wire is the way to go. I just yanked a 9 pin connector and wire from an old serial mouse.

Originally Posted by rando

That's it. As soon as the device gets power it will start to pump out an NMEA stream 4800/8/n/1.

Worked for me too. Spend about 20 minutes to solder seral connector. Thanks.