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2003 - 2009, roadster, coupe, facelift
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GuidoK
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Post by GuidoK » Sun Oct 14, 2018 8:03 pm

Nick9one1 wrote: Sun Oct 14, 2018 7:43 pm
GuidoK wrote: Sun Oct 14, 2018 7:22 pm
No its not. In the first place the obd2 speed info is not accurate at all (the 1 or 2 mile speed difference are the 1 or 2 miles that take the longest to overcome!) and in the 2nd place the obd2 update speed is slow and not a constant.
If you use a usb otg OBD2 module rather than Bluetooth the response speed is much better, I'd say a lot faster than 10hz.
Also, torque displays the 'real' speed. Not the corrected speed like the clocks.
If torque displays 'real' speed it can only be on basis of the internal phone gps.
As I've explained that is totally unsuitable for acceleration measurements because it releases its NMEA data with 1hz. Much too slow.
As far as obd2 speed is concerned, there is only 1 signal and that is very inaccurate. GPS speed is well within 0,1m/hr, a whole magnitude more accurate than the obd2 speed. And as I also explained, the obd2 signal is not a consistent signal, Its inconsistent, depending on how much data is sent over the canbus. ITs a serial bus typology, so update speed is dependant on how much is sent in communication between the 10 or so cpu's that talk over that bus. Unsuitable for accurate measurements, Sure you will get a value, but no accuracy within reasonable certaincy (yes 1 second or so but that's worth nothing in these times you want to measure, you need at least 4 or 5 times that accuracy to have a value that means anything).

Buy a 10hz gps, do some measurements and you will understand what I mean. If you get some measurements that are bang on while other measurements differ 0,5sec or more, that means the system is s###.
Thats why NO party that wants to do measurements that bare ANY credibility (like magazines etc) uses an obd2 based system and ALL use a 10hz GPS based system or faster (like vbox), or if they can afford it even more (professional) systems like radar.

BTW bluetooth is easily fast enough to send a 10hz NMEA datastream so if bluetooth is not fast enough for obd2, that means your connection or transfer is very very bad. To give you an example, KKL bus speed topology is about 100 times(!) as slow as bluetooth 1 (which is ~1mbit). Bluetooth 2.0 (since 2004) is ~3 times faster than that. So easily fast enough for the datatransfer. If that has any impact its because of bad hardware (fake interface chips?) or bad software.
CAN bus (the fastest of the 2 variants) is between 2 and 6 times as slow as bluetooth so that also doesnt have to be a problem when protocols are implemented correctly.

Which type of OTG OBD2 adapter are you using? ELM327 based?
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