Photon - interfacing with GPS

General
1

Hi - This has got me bugged and am seeking some advice.

I have a Photon connected to an adafruit Ultimate GPS - the GPS is powered by a USB power supply seperatly from the Photon (yes the grounds are connected).

This works perfectly.

I have another GPS (a GP-20U7) connected directly to another photon. (Powered from either 3.3v or 5v - depending on my mood).

This works in the sense that I get NMEA sentences but I do not get any fix info.

SO I swap the GPS’s

The GP-20U7 connected where the adafruit one was and powered by seperate power supply works perfectly.

The adafruit one connected directly gives me NMEA sentences but no fix information.

The adafruit pull 25ma and the GP-20U7 pulls 40ma.

According to the DOC the photon can supply a max of 100ma on the 3.3 line and 1A on the 5v line.

The hardware in both cases seems to be ok - in that NMEA sentences are sent from the GPS - it is just with the GPS powered directly by the photon it does not seem to get a fix. The adafruit has a fix LED which will go out when it has a fix - it just blinks the ‘I have not got a fix’ pattern when directly connected to the photon for power.

I Got a tad desperate and put 4 layers of foil between the Photon and the GPS - just in case the GPS needed shielding (told you I was desperate) - but this made no difference.

Eventually the GP-20U7 will be connected to an electron - but for the moment I am simulating the electron code on photon’s.

Any ideas why I would not get fix info when the GPS is directly connected to the photon?

Note both Photon’s and GPS’s are within 6 inches of each other - one working and one not working!

Stan

2

Maybe even 1 inch is too much.
The only safe way to get a clean signal is an open unobscured sky.
What does the NMEA tells you?

3

As I mentioned, the NMEA is valid but does not contain fix information (because the GPS has not got a fix).

Last night I replaced the second photon with an electron with the GPS (Adafruit) wired directly. Worked perfectly with the same code as on the other photon with the GPS seperatly powered.

On the ‘baulky’ photon, I wired 2 x 0.1 uf ceramic caps plus a 10 uf Tant electrolytic cap across the power/ground in case the power signal needed filtering - no difference, however I will try again because I had the caps at the photon end rather than at the GPS end which I understand is where I should have put them!

There is one more test I need to do and that is to swap the good photon with a GPS that is seperatly powered and working great with the photon I was using to directly power the GPS just in case it is a photon specific issue.

Lets see what happens tonite.

Stan