Harry's GPS Suite Forum

Hello all, wondering if any of you have experienced an issue of erratic / choppy OBD data readings after connecting an external GPS sensor (in my case a Dual XGPS160). My OBD device is an OBDLink MX+, which works flawlessly when the external GPS sensor is not connected. Here is a link to the video for reference. Any help would be much appreciated!

https://youtu.be/N8mcUUQkTO8

Yes, this is known problem discussed here on the forum already. Sensor fusion joining GPS and OBD (and IMU) fixes results in choppy / stepped OBD data for certain update rate combinations from GPS and OBD. I have tweaked the system a bit for v24, but it looks like it isn't fixed.

Question: which update rates are reported for the XGPS and MX+ typically, please check in Sensor List.
You can try tweaking the storage rate in Expert Settings too. Set it to 5 Hz, 10 Hz, or 20 Hz to see if this results in smoother results. Please note that changing the storage rate will have an effect for new recordings only.

- Harry

Thanks for the reply Harry. So my update rates for the XGPS160 is 10 Hz and for the OBDLink MX+ around 4-8 Hz (it fluctuates). Looking at the engine data in real-time, the reading seem to be very smooth with no choppy/erratic measurements. So it appears this issue is during LapTimer mode only?

Data is coming from several sensors with a specific timing each. When displaying data, LapTimer always uses the latest available fix for the sensor type shown. So this is "as is" data. This situation changes when multiple sensor's data is stored with a common timestamp. This process is named "fusion". It interpolates all channels to have a common time line before the data is stored in one "fix" representing GPS, OBD, IMU, tires data combined. It is this fusion step showing problems.

- Harry

Ok, so I went ahead and changed the storage rate to 5 Hz in Expert Settings. Is there a way to simulate LapTimer without being on track? I’d like to test this out before my next actual track day.

Thanks again.

Pure simulation - probably not. Exporting existing laps to e.g. VBO and importing it again will result in a new lap with 5 Hz rate. But the input will be "stepped" for OBD already. This revaluation will smooth things a bit, but not fix it.

But you can test it easily. Enable "Manual Timing" in LapTimer's Settings. On your way to work or elsewhere, press Start in Timer View and Stop a minute later. This ad hoc recording will be available in Lap List as usual.

- Harry

Ok, so I did some testing at various at rates and I’m still getting quite a bit of “stepped” data. Once I disconnect the XGPS160, the OBD readings smooth out. I’m pretty bummed about this because I made sure to use the recommended Bluetooth sensors, and I’m experiencing these issues.

You mentioned this issue may be fixed for v24, I noticed I’m still running v23.0.11. Is this not the latest version?

*edit* Nevermind, just read the process to request v24 Beta.

Thanks,

Ronnie

This is not a sensor problem, it is a problem in the software. The initial v24 will show the same behavior as before, but I plan to work on this for an early bugfix release.

Hi Harry,

The last time I used LapTimer was in September of 2020. I purchased a Dual XGPS150A right before this event. I believe that it can update 5 times per second. I had similar issues to what RonnieB described. Were you able to make any progress on this? If not, do you have any recommendations on what settings to use to avoid this issue?

Thanks,


Chris

Still on my list for further investigation.