It turns out that under a truly open sky, after being given a couple of minutes to lock in, relative accuracy within a couple of feet is doable if you are using one in a mobile bot to find another. Let me explain the “if”…
You will get some “chatter” that will make it appear that you are moving around in a small area. I have not ever had it return only one exact location over and over. But under open sky, that small area it will report is about 6’x 6’ and if the unit is completely still and has no obstructions moving around it, the majority of the positions reported will be a single location. Anyway, within a 6’x6’ area, just circling is likely to be adequate to physically encounter the unit with the other GPS.
As far as absolute accuracy, I can’t say for sure that GPSVisualizer (which uses Google mapping) is 100% valid, but the tests I have done (like the parking lot picture in this thread) are pretty much dead on.
I wished I’d known this before ordering a $60 LS20031 :( Which ended up DOA :( Could’ve saved a lot of money…
Well, I have one of these on order now. I will try to remember to post up if I am able to send data / configs to it on the remaining pin. That has to be the RX pin, right? It’s a SirfStar III chipset, so when it arrives, I’ll try sending known commands for the chipset…
I have not used the Rx pin. The easy/safe way to test it would be to loop back on the USB adapter without the GPS attached - just clip a lead running from the one we know is going to Rx on the PC to the one we are pretty sure is going to Tx. Bring up a terminal program , type a character and see if it is echoed. Obviously I have not tried sending commands, but yes the GPS-500 is a SIRFstar-III. The GPS-360 is a SIRFstar-II. My most recent tests with the GPS-500 on open water went amazingly well. Given an open sky, I don’t think you will find a more reliable and accurate GPS without spending a lot more money to get a high end Garmin or Trimble.
Anyway, I might get a chance to try the loopback tonight.
I tried to find more information about the other pins the Pharos 500 but there isn’t much online. I think that the Pharos Tech Support would likely email the pinout if you told them that it was for a hobby project and not a competing product. Anyways, here’s the two links I did manage to find. [Link 1] [Link 2]
I verified that the pin in question (leftmost, next to GND) is the PC’s TX pin. Used an oscilloscope (fewer hands required vs loopback). Have not yet been able to get the GPS to respond to proprietary sirf III commands.
Which one? Beats me; that’s what makes reverse engineering interesting. I don’t know whether that will work or not, but it certainly can’t truly need 2 ground pins, so it may be that one of them is a mode pin and tying it to ground puts it in “spit out data” mode. I tested another GPS that had that sort of pin.
i’am new here and to electronics also I’am now searching for GPS receiver for less than 60$, and i would like to ask if someone compared mentioned here gps360/500 with FMP04-TLP GPS (25$ http://www.ohararp.com/products) based on MediaTek Single Chip Architecture (MT3329) and LS20031.
I was thinking also bout spending little extra on FV-M8 (http://www.sparkfun.com/products/8266) but is it really that good as they mention on sparkfun? (9 sats indoors)
I got a 7-8 sat 3d fix in the garage last night with the iGPS-500. I am able to get fixes not just inside but in the basement.
The San Jose module looks like the same chipset as the Locosys and the same software (MiniGPS from MediaTek) works on it, but the Locosys does up to 10Hz if that matters.
Although I’ve had bad luck with mine… the first one was bad, the second worked but never all that great, and I broke off the RF shield and have tried repair but never got it working as well as the iGPS-500.
Depending on what you want to do with it, the iGPS could do the trick fine. Plus if you can find the $18 deal on amazon that is hard to beat. To me the big downsides are the fixed 4800bps comm and lack of configurability.
I haven’t had a chance to test the other two pins that we suspect might be serial RX to receive commands. Even if one works as an RX, there isn’t a lot that you can do, as far as I can tell, with the SiRF StarIII chips. The MTK chip on the Locosys is extremely configurable. Quite nice.
So no luck with having it respond to commands? Another possible avenue for investigation would be to buy it on eBay with the software (if you look hard, you can find pretty much the same price) and hook up someting to spy on the pin for data to see if they send anything to adjust set up. Sometimes proprietary protocols are very thin wrappers for the chipset, like a byte or two as a command to pass through the nexte few bytes as a chipset command. For my purposes, a reliable position updated every second or so is fine.
Haven’t gotten that far yet. Just soldered two wires onto the half-pins and measured voltages (both show a voltage, incidentally). I had previously measured voltages on the usb serial adapter and found one pin grounded and the other not. Have been up to my ears in trying to get my autonomous robot navigating, but will revisit this question in several more weeks after the competition is over and I’ve begun sleeping again. :) I’m with you, a good position update every second at 4800bps seems to be entirely adequate.
I followed your posts about hacking open the gps500 and using it with arduino and it works perfectly. Thanks for the info.
I wanted to also use the usb to ttl cable that came with the microsoft gps. Is there any disadvantage to this cable for programming?
It looks like a 12 pin cable so I assume every 2 pins connect to the pin out on the gps so it wouldn’t be too hard to find the pinout and solder on a header socket to the end would it?
Back when I was using that Pharos GPS in a few projects, I bought a Streets package (software and hardware) for about $5 thinking I was getting another Pharos. It turned out to be a Novation 168, which is a one piece unit with the USB on the same board and no edge connectors. So it sat on my shelf a long time. I needed another GPS recently and I decided I needed to either figure out how to use that one or get rid of it. When I put it on the shelf, I figured I would use it on the PC but I really haven’t; there just isn’t much interesting to do with a GPS on a machine that sits in one place. Anyway, I cracked it open and figured it out.
Yes, I am using it on a PC, but as you can see it isn't plugged in directly with USB; I am using an FTDI cable. After this test, I hot glued it back into the bottom housing and hot glued the wires to the housing on one side for strain relief. Anyway, FTDI provides 5v and sends/receives data at TTL level; if it works on the cable, it will work with the Arduino.
I don’t know whether that will work or not, but it certainly can’t truly need 2 ground pins, so it may be that one of them is a mode pin and tying it to ground puts it in “spit out data” mode. I tested another GPS that had that sort of pin.
I’am now searching for GPS receiver for less than 60$, and i would like to ask if someone compared mentioned here gps360/500 with FMP04-TLP GPS (25$ 
