GPS with PPS output

Note: all files and sketches on M0IFA.me

I have been using a  GPS board with 4 pins VCC-GND-TXD-RXD in a clock project and it works very well using the TinyGSP Arduino library.

QCX+ on top of GPS CLOCK

The sketch is  GPS_CLOCK_TFT. To get out the PPS signal from the GPS module which did not have a PPS pin output, I soldered a tiny wire to the 1K resistor connected to the GPS receiver pin 3.

Wire on PPS output of receiver

On test with the QCX+ inputting the NMEA GPS TX signal and the PPS signal via the "Paddle" input to the QCX+ I found that it did not operate reliably. So I checked, and found the output voltage levels from the GPS module were 0-3.2V. In the QCX+ manual it says the GPS inputs should be 0-5V levels and at least < 1.5V to > 3.5V. So it seems I cannot directly interface the GPS and QCX+...

So I wired up this 3v3 to 5V converter:

And low and behold the QCX interface worked just fine. i was able to easily calibrate both the Reference (menu 8.11) and the System (menu 8.12) oscillators from the GPS PPS input. While calibrating I set the Practice mode (menu 4.7) "ON" to prevent any possible transmissions, I don't know if the is mandatory or if the calibration happens without the GPS triggering the TX.

Here's the inside of the GPS CLOCK with the converter installed

Inside the GPS clock

The GPS clock, Time, Locator and Date