Connecting old handheld Magellan Explorist GPS to computer via serial - Page 1
Forum section: electronics / projects

author: soldar
author_rank: Super Contributor
timestamp: May 02, 2024, 04:10:38 pm
content: For many years I had an old Garmin Etrex GPS, the original yellow model. It worked on 3V (2 x AA). I could connect it to my computer and download and upload tracks, waypoints, etc.It would connect to the serial RS232 port but it used 0V and 3V levels. The computer did not seem to mind and everything worked well.This model had a weak and unreliable display connector and always ended failing. I had three in total and they all failed in the same way. I gave up.Recently I was gifted (donated, presented, junked) a 2004 Magellan Explorist 300. Externally it is very similar to the old Garmin Etrex.I have tested it and it seems to work OK except that the date is off by 1024 weeks (19.6 years, 7168 days) due to it not being prepared and understanding the 1024 week rollover. Not a major thing.https://en.wikipedia.org/wiki/GPS_week_number_rolloverOther than that it gets the location and time of day right.I would like to connect it to the computer like I did with the old one. It does not have an external connector but it does have a hidden port which seems very similar and I might get lucky and get it to work.The main issue is that I need to make some kind of tiny connector, with pins that go through holes and it is difficult to make somthing and have it hold in place.The hidden port is in the battery compartment. It has four contacts, Gnd, Txd, Rxd, Vcc. I am ssuming for now they work like the old Etrex.The connector I make needs to have those tiny pins spring loaded.Of the four contacts, the upper right is connected to the negative gnd and the battery big rivet on the right.The upper left contact is directly connected to the battery + Vcc and the corresponding rivet on the left. So those two can easily be connected to the rivets/springs but the two data pins still need to make contact.I cannot think of a really easy way to make a reliable contact for testing. The only place to hold anything is the female screw thread for the cover and it is #4-40 thread and I do not have screws with that thread. Only a standoff from a computer to confirm the thread.I would like to do some quick and dirty testing to confirm if it can communicate with the computer. I need to handle the unit and use the front buttons so it's not like I can just place it face down on the bench and drop some pins in there.Any ideas?

author: themadhippy
author_rank: Super Contributor
timestamp: May 02, 2024, 04:23:42 pm
content: whip the back of and find somewhere on the pcb to solder 4 wires,if theirs space bodge in a 4 pin jack socket

author: coromonadalix
author_rank: Super Contributor
timestamp: May 02, 2024, 04:24:57 pm
content: to simply your life you could take ftdi or any usb to serial 3.3v interface, do your connection and try with a terminal software if the garmin spit some stuff when it boot1st test is the tx rx shorted together in the garmin if the chars ... are echoed, if you are sure of the TX and RX line ...unless this port get disabled once factory programmedmaybe the pins are .05 " spacing instead of the 0.1" one we see oftenoh pogo pins thats what they are called, they have a spring in them

author: soldar
author_rank: Super Contributor
timestamp: May 02, 2024, 06:10:59 pm
content: Quote from: themadhippy on May 02, 2024, 04:23:42 pmUm, no. It is waterproof, hermetically sealed with rubber all around. I do not want to destroy it unnecessarily.

author: Ian.M
author_rank: Super Contributor
timestamp: May 02, 2024, 06:16:54 pm
content: Although NMEA 0183 is logic level, it is the same polarity (mark low) as RS232,and is inverted with respect to 'TTL' serial from a FTDI or other USB UART. You need to figure out some way of scoping the TX signal to confirm whether or not its inverted, even if you have to resort to wedging in some bare ended wires with matchsticks!

author: soldar
author_rank: Super Contributor
timestamp: May 03, 2024, 09:31:34 am
content: Quote from: Ian.M on May 02, 2024, 06:16:54 pmWedging toothpicks is just the idea I needed!I did a first try but no result. Connected the GPS directly to the serial port, as I did with the old GPS, and I tried connecting from the computer with HyperTerminal but there was no reaction. In my past experience even if baud rate or other parameters were not right I would get some garbled response.I suppose it could be that the contacts were not good. At this point I suppose the next step would be to monitor voltage and signals on the lines but I think I am giving up because I do not think it is worth the effort.I am assuming the serial signals do not need voltage level translation. This might not be so.I am assuming they are plain serial and this is most likely so but there is a very small chance they are USB.Even if I manage to communicate with the GPS I would have to see if I can download waypoints, tracks, etc. which might require determining formats and protocols. maybe even specific software.Too much effort for such an old and outdated device.Right now I can mark points and later retrieve the coordinates manually which is a PITA but will have to do.I wish I could buy a new, similar unit for under $50 but the cheapest I find isGarmin - eTrex SE 2.2" GPS with Built-In Bluetoothfor $150 + tax and just not worth it to me.I just like to record my tracks when I travel and save them to my computer and Google Earth.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 03, 2024, 08:51:27 pm
content: I have a very similar unit (explorist 210) but the contacts are outside the battery compartment and they sold a cable that screwed to the body. The cable contacts were something like small Pogo pins. IMO, my phone with a free app (GPStest) is so much superior to the old dedicated GPS that I never use it anymore. Better sensitivity, faster lock and probably more accurate. I wouldn't waste much time with the unit, especially without the external interface.

author: soldar
author_rank: Super Contributor
timestamp: May 03, 2024, 10:15:55 pm
content: Quote from: Conrad Hoffman on May 03, 2024, 08:51:27 pmIs it serial or usb? What software? Can you download tracks and points to the computer?-I prefer to have a separate device and not use the phone.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 04, 2024, 02:52:58 am
content: You can look it up online, but I remember it as USB. I also remember probably having to load a serial-USB driver so it's basically serial. I think it could download waypoints, but not sure. I mostly used the computer interface with an obsolete program to average position and improve accuracy. That might have been when GPS was purposely randomized with "selective availability".

author: soldar
author_rank: Super Contributor
timestamp: May 04, 2024, 08:35:21 am
content: Thanks. I might try connecting as USB and see if I get anywhere.Do you remember if you had to select in the menus some kind of "data transfer" or "connect to PC" option? Because mine does not have it so it would have to happen automatically upon connection.Even though the original yellow Garmin "12 satellite" fail at the screen connector, I might end up just buying one if I can get it for under $30 because it is exactly what I need.Looking at the Explorist 210 manual I seeQuoteSo it is possible the device detects the USB connection and starts up in data mode. I will have to try.