GPS support

[Finchiedev]

We have at least 2 of Adafruit's Ultimate GPS Module, and with that the following functionality needs to be implemented:

• Parse NMEA sentences
• Enable on-board data logging
• Detect when PPS output shows fix

I'm not sure yet that we actually have a use for all of these features, but building them is fairly trivial and should give some valuable experience, plus it would be nice to have these to come back to later.

[Finchiedev]

Currently I am having trouble getting the GPS to lock to satellites. This is reproducible on 2 separate chips, so most likely there is an issue with signal acquisition (maybe not giving enough time in good range?)

[LukePrior]

The Adafruit guide recommends a 3V active GPS antenna so it may be a good idea to acquire such an antenna.

Core Electronics are local and sell the Adafruit branded ones:

• https://core-electronics.com.au/gps-antenna-external-active-antenna-3-5v-28db-5-meter-sma.html
• https://core-electronics.com.au/sma-to-ufl-u-fl-ipx-ipex-rf-adapter-cable.html

[LukePrior]

I've also noticed that the Adafruit module we have only supports the US GPS network and not GLONASS, BDS, GALILEO, QZSS, etc.

We ideally need a device which supports all of these networks along with dual band support to get optimal location accuracy.

I just checked on my phone and it is can see 44 satellites from 5 networks.

[LukePrior]

We would ideally want one of the ZED modules from uBlox such as the F9P as they offer the best accuracy but they are not cheap so we will probably have to settle for something cheaper.

• https://core-electronics.com.au/sparkfun-gps-rtk2-board-zed-f9p-qwiic.html
• https://core-electronics.com.au/sma-to-ufl-u-fl-ipx-ipex-rf-adapter-cable.html
• https://core-electronics.com.au/gnss-multi-band-magnetic-mount-antenna-5m-sma.html

$620

Cheaper option using the same GPS module and antenna for $425: https://au.mouser.com/ProductDetail/ArduSimple/AS-STARTKIT-BASIC-L1L2-NH-02?qs=GBLSl2Akiru%2FUw8RAcKyUw%3D%3D&mgh=1&vip=1

https://m.youtube.com/watch?v=3tQjIHFcJVg
https://deepsouthrobotics.com/2019/06/03/the-taming-of-the-u-blox-zed-f9p/

[Finchiedev]

Thanks for your input, @LukePrior. Some updates:

• I have managed to get the GPS module consistently acquiring signal after about ~1min in an open area with sky access
• It would certainly be nice to have an active antenna, but it may be worth considering the power/cost factors. Theoretically it would be fairly simple to set up an additional Arduino (or maybe even use the same one) to emulate the GPS device in the meantime for situations where we are either rapidly prototyping, without sky access or both
• You are definitely right about multi-network support, and as the video mentions BeiDou would probably would be the best for Australia at least

I think the best plan of action for now is to add support for this GPS board in a modular way so that it could theoretically be swapped out in the future. The software should be able to support multiple different boards & positioning systems at once, and provide some way to emulate via software as a more cost-effective option until we have actually acquired the parts.

[Finchiedev]

A good reference for building first-class support for the MTK3339 is https://cdn-shop.adafruit.com/datasheets/PMTK_A11.pdf