Playing with the SUP500F GPS module

The SUP500F is a pretty nice unit: small, low power consumption (33mA), 10Hz update, and quick start up time (29 second cold start with an open sky).

Here it is on the breadboard:

I’m using a MAX232 to convert the RS-232 voltages from the PCs serial port to TTL (5V), and a simple voltage divider to reduce the 5V TTL signal to the 3V required by the SRF500F’s UART.

Initially there was no signal on the TX pin, and a square wave with a 4 second period on pin 6 (the documentation states this pin should have a frequency of 1Hz). This behaviour was reported by a couple of other people on the sparkfun forum. After a bit of trial and error I got the expected behaviour by setting VBAT to +5V, and PSE_SEL to GND.

If you view the serial port output with something like TeraTerm (9600 baud 8N1) you can see the NMEA messages streaming out of the GPS unit:

...
$GPGSV,3,2,12,10,31,120,,29,27,214,,10,15,336,,04,11,132,*7B
$GPGSV,3,3,12,31,09,212,,21,03,320,,27,04,355,,31,00,217,*76
$GPVTG,000.0,T,,M,000.0,N,000.0,K,N*02
$GPRMC,130122.000,V,0000.0000,N,00000.0000,E,000.0,000.0,220302,,,N*79
$GPGGA,130122.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,0.0,M,,0000*68
$GPGSA,A,1,,,,,,,,,,,,,0.0,0.0,0.0*30
$GPGSV,3,1,12,14,82,367,,05,56,055,,22,51,246,,02,32,144,*71
$GPGSV,3,2,12,10,34,171,,25,22,233,,06,12,316,,04,12,182,*72
$GPGSV,3,3,12,30,09,239,,24,08,300,,27,04,355,,31,00,217,*77
$GPVTG,000.0,T,,M,000.0,N,000.0,K,N*02
$GPRMC,130122.000,V,0000.0000,N,00000.0000,E,000.0,000.0,220302,,,N*78
$GPGGA,130122.000,0000.0000,N,00000.0000,E,0,00,0.0,0.0,M,0.0,M,,0000*69
...

If you like your GPS data to look a bit prettier, you can use the SkyTraq GPS Viewer software available on the SparkFun website:

It took about 5 minutes under an open sky for it to get a fix the first time, but since then its been very fast: 30 seconds if its been off for more than 30 minutes or so, and under 5 seconds otherwise. The initial delay is because the GPS unit has to download the almanac (a coarse description of all satellite orbital information, valid for a few months), and the ephemeris for each visible satellite (a precise description of the satellite’s orbital and clock correction information, valid for 30 minutes).

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