BT1 and Data Rates

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mculik5
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BT1 and Data Rates

Postby mculik5 » Mon Mar 21, 2016 6:31 pm

Hi.

Just purchased the GoPoint BT1 to use with HLT GP Edition (19.0.31). I'm also using a Dual XGPS 160. Everything works fine together, but I'd like to optimize the BT1 update rate to smooth out the tachometer/TPS overlays in video.

When I got the BT1, I did a few test drives near my house to gather some data. When I checked HLT before driving, it said the BT1 update rate was 3Hz. Here's my confusion:

When I exported and reviewed the data, it showed an average of 9.2 data points per second, with a min of 4 and max of 11. Looking at some 1-second long groups of data points where I was at full throttle, each point shows a RPM increase. Thus, unless RPM is extrapolated, it would seem that the BT1 update rate is actually much better than 3Hz.

Three questions:
1. Can someone explain what each data point in HLT actually is? Given the claimed 10Hz from the GPS and actual 9.2Hz average I achieved, it would seem the data points are based on GPS, with accelerometer and OBD data added to each. Is that correct?
2. What does the 3Hz that HLT shows for the BT1 actually mean?
3. How is OBD data applied to data points if the OBD update rate slows down? Does it just apply the same OBD data until it gets new data?

Also, most important question:
4. What settings can I change/what things can I do to increase the BT1 update rate to smooth out the video overlays?

Thanks!


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Harry
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Re: BT1 and Data Rates

Postby Harry » Mon Mar 21, 2016 10:41 pm

Hi,

1. Yes, GPS dictates the storage rate and acceleration and OBD fixes are interpolated to this GPS fixes. This means GPS data is what has been received and OBD / acceleration data associated is derived data. You will hardly see a difference between a 10 Hz and a 3 Hz OBD data rate by the way. During overlay, the GPS (augmented with OBD and acceleration) data will be interpolated to each video frame (25 or 30 Hz).
2. 3 Hz means 3 OBD fixes per second. A fix is a full set of OBD channels (PIDs). Not every PID is requested during each loop, so instead of 10(?) PIDs each OBD fix contains, only 5 are requested in average per fix. So another interpretation of 3 Hz is 3 * 5 PIDs = 15 PIDs received per second. A PID or channel is a single value like rpm or throttle position.
3. See #1, interpolation will result in smoother data the lower the rate is. The lower it is, the more peaks will be missed.
4. Not too much. LapTimer GrandPrix includes a small acceleration for BT1 update rates, please make sure LapTimer ‣ Administration ‣ Settings ‣ Expert Settings ‣ OBD Tweaks ‣ Sequential Request (BT1) is in position OFF.

Possible update rates depend a lot on your car's bus protocol. In case it is a CAN bus, you should get something between 6 and 8 Hz (i.e. 30 to 40 PIDs / s). For older buses, 2 Hz (i.e. 10 PIDs / s) is a typical value.

- Harry


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mculik5
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Re: BT1 and Data Rates

Postby mculik5 » Tue Mar 22, 2016 3:59 pm

Thanks. Very helpful.


jwmelvin
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Re: BT1 and Data Rates

Postby jwmelvin » Wed Mar 30, 2016 7:29 pm

Harry, is there a good approach for a vehicle with a really slow bus? I'm seeing 1 Hz reported for my NSX and the BT1 or Kiwi3. If I could limit to just speed and throttle PIDs would that help?


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Re: BT1 and Data Rates

Postby Harry » Thu Mar 31, 2016 2:18 pm

It is possible to exclude PIDs in Expert Settings. The string needs to consist of 4 digit sequences made up from hex mode plus hex PID. Something like 010C.

Only removing MAF, MAP, RPM, VSS, TPS has a relevant impact, all other PIDs are requested seldom. You may want to try VSS because speed is coming in from GPS too.

Harry


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