Problems with update rate on DIY GPS

So I am trying to build a DIY GPS using the Beitian BN-220 GPS module. This GPS chip is capable of 16.7Hz or 60ms update rate when reconfigured for US satellites only. I am also using an HC05 bluetooth module and have them connected on a breadboard until everything is working properly. Both GPS and Bluetooth baud rate was raised to 115200 to handle the extra data. In U-Center the GPS was working fine at 16.7Hz.

When I tried to connect to RaceChrono, initially it was reading at 16.7Hz in the app and everything looked good for 10-15 seconds and then the update rate suddenly went to 1Hz and stayed there. The data rate was still around 60kbit/sec but the LED on the bluetooth was flashing slowly, backing up the 1Hz reading. The GPS LED continued to flash rapidly. As soon as I ended the session, the LED on the bluetooth starting flashing quickly again. I tried a few things including a second bluetooth module and could not get it to repeat this. It will only do 1Hz in RC now. I reconnected the GPS to the PC and it was still running at 16.7Hz in U-Center. Anyone have any ideas what might be happening? I am trying to figure out if it is a hardware problem or some type of software/configuration problem. Thanks

Comments

  • If you communicate using the Bluetooth serial protocol and NMEA, it maybe useful to copy paste few seconds worth of NMEA here. If it's stuck at exactly 1 Hz in RaceChrono, I bet it's really 1 Hz or the timestamps are missing decimals. If the Hz rate varies, then it maybe a Bluetooth bandwidth issue.
  • Thanks for the advice. It was hovering around 1Hz and not stuck there. I double checked the Bluetooth module and I had the baud stop bit messed up. That did not fix the issue though. So I then reconfigured the GPS to only output RMC and GGA sentences and now it works. Now I just need to wire everything up in a 3D printed box.
  • Is the output frequency always stable at 16.7Hz? Or sometimes does it decreases?
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