GPS modules MKT3339 vs A2235-H

[David Forbes]

I am looking into GPS modules for my scope clock. There appear to be a few out
there.

The Maestro A2235-H is sold by Mouser for $14. Speaks NMEA.

The MKT3339 is sold by Adafruit for $30. Also speaks NMEA. They have some
software for Arduinos.

Has any of you used either of these modules, and if so, what was your experience?

--
David Forbes, Tucson, AZ

[John Rehwinkel]

> I am looking into GPS modules for my scope clock. There appear to be a few out there.

Yes, I've played with several of them.

>
> The Maestro A2235-H is sold by Mouser for $14. Speaks NMEA.
>
> The MKT3339 is sold by Adafruit for $30. Also speaks NMEA. They have some software for Arduinos.
>
> Has any of you used either of these modules, and if so, what was your experience?

I tried the MTK3339, and had repeated problems with it going into a strange mode where it would switch to sending vendor-unique PMTK sentences instead of the standard NMEA ones, and would refuse to respond to commands. Searching the internet for clues revealed that other people had similar problems, and several fairly superstitious sounding "fixes", none of which worked reliably for me.

Since NMEA is NMEA, most software for one of them will work for others. I ended up rolling my own in the end. NMEA isn't hard to parse, but converting coördinates from direction and degrees/decimal minutes to signed decimal degrees requires either floating point, or some creative juggling with integers. My code is part of a project I'm not free to share, but I could strip out the GPS portion if you're interested.

I also looked at the available task schedulers available for Arduino and ended up rolling my own for that, too.

- John

[Oscilloclock]

For my lower-end units I use the NEO-6M-C module (from seller waveshare on eBay), as I wanted a 5V tolerant module and this was one of the more reasonable ones I could find.

Note that the NEO-7M module from the same supplier doesn't have EEPROM, so you have to send the configuration instructions each time the unit powers up - this is rather annoying so I stay with the 6M.

[Dave]

You can get the waveshare unit for $19 shipped off aliexpress:
http://www.aliexpress.com/item/Waveshare-UART-GPS-Module-NEO-6M-C-Compliant-with-UART-GPS-NEO-6M-High-gain-Active/1973062729.html?spm=2114.30010308.3.18.d8DX3g&ws_ab_test=searchweb201556_6,searchweb201644_3_10014_10001_10002_10005_301_10006_10003_10004_62_61,searchweb201560_2,searchweb1451318400_6149,searchweb1451318411_6452

[gregebert]

I've never used a GPS receiver module, so I'm wondering if the units typically do all of the calculations and provides lat/long info, as well as time (UTC I assume)  ?   Is the receiver sensitive enough that a small indoor antenna is sufficient ?

[David Forbes]

The typical GPS module has a built-in antenna, and it provides an NMEA
standard serial interface which has lat/long and time, as well as a 1PPS
output.

I have already written code for my previous scope clock to parse the
NMEA strings.

I also am providing a DS1307 RTC chip with backup battery, for just in
case. Software can find out if the GPS module is locked to its signal or
not, and switch over gracefully.

--
David Forbes, Tucson AZ