Bluetooth Data Acquisition

andylaurence

Some of us are running cars without OBD-II. Would it be possible to use a Bluetooth device to read sensors on the car for things like wheel speed, engine speed, throttle inputs, accelerometers and the like? I'm thinking something like this Bluetooth DAQ, which has 8 analogue inputs, Alternatively, "grow your own" with something like this Bluetooth serial device, which allows connection of serial devices. This means you can connect any serial data acquisition device to allow connection of your sensors.



As for sensors, you can have lots of inputs:

3D accelerometers (although the new RaceChrono beta supports this with the right phone)

Optical sensor (wheel speed reading on ABS sensors, for example)

Driver heart rate

Distance sensor (how close are you to the car infront?)

Temperature (oil/water/intake)

Oil pressure

Brake pressure

Throttle position

Damper positions



Alternatively, importing of data from a data logger
like this would be great. Any thoughts?



Cheers,

Andy

aol_of_RaceChrono

Everything is possible to support, the only problem is choosing what to support :) But certainly with those gadgets you got my attention!

The external data channels (like the OBD-II) are bit tricky as there is time stamps for the GPS but not the data channels. And synchronizing the external data to the Bluetooth GPS timestamps isn't too easy, as the lag depends on the connection and on the device.

So an ideal device would be one that would receive all channels as well as GPS, and possibly would back up them to SD. The device could then time stamp the accelerometer data, as it can trust the data is received with fixed time offsets, and send it all through one Bluetooth connection to RaceChrono. Also it could buffer the data to the SD if Bluetooth has disconnected, so data is not lost before reconnecting.

I even believe such device could have commercial potential. Too bad I'm clueless about electronics R&D :)

andylaurence

OK, how about a Bluetooth RS232 device and some stackable hardware? Use the 8 input analogue device and the digital input device (will even read turbocharger RPM if you can find a sensor) to read in whatever data you need and the RS232 input device for GPS time. Of course, this example isn't great as the devices can only sustain an 80Hz sample rate split between the lot. There isn't much in the way of cheap data loggers, although there are proper data loggers, intended for car use, such as the DynoStar GPS, which has 2D accelermeters, 7 analogue inputs (12.5Hz sample rate), 4 digital inputs (100Hz sample rate), tacho input and the required GPS. It's cheap too, although another league from the SD data logger I linked to earlier.



I'm sure someone with some PIC knowledge could interface something like this with a GPS receiver and use the 13 analogue inputs for something useful. That's beyond me, though.



Cheers,

Andy

andylaurence

How about this device, which logs wheel speed, engine speed and g-force along with time and date? Data is downloaded via USB. It's got a nice display, a few other useful features and it's cheap too!



Cheers,

Andy

aol_of_RaceChrono

Not sure, seems like it doesn't have a GPS. The logged data might be hard to sync GPS data... Quite cool though.

andylaurence

It doesn't have built-in GPS but it does timestamp the data. By manually setting the time, could it be close enough?



Cheers,

Andy

aol_of_RaceChrono

Probably not, as it needs to be within half a second to be useful at all... So manual time setting is not good option. Half a second is easily achieved by connecting to external (Bluetooth) data device like OBD-II reader, but if better sync accuracy is needed, things get tricky.

Perfect sync is possibly achieved only if the data sources are integrated to the GPS input, like some professional data logging device. But the accelerometer / OBD-II sync may be improved by some computing, but only if the sync is already close enough. I've been investigating this but not working yet.

andylaurence

In which case, I'll stop looking because I don't think you'll get anything better than the DynoStar for the money.



Cheers,

Andy

aol_of_RaceChrono

I could probably add a DynoStar import if I get some sample files. I guess you could send me some if you are going to buy the system?

johntorg

I just tested the Alpha-Bid OBD2 on My 2003 VW 20th Anniversary GTI. It appears to work, although I haven't looked at the sync problems. I didn't notice anyway to pick up the Brake on/off. this would be useful to look at braking points around the track.

aol_of_RaceChrono

I don't think the brake on/off is available at OBD-II. But I think the RaceChrono is quite accurate there already, as the braking point are currently determined from the speed (the hi/lo speeds mode).

andylaurence

I've just bought one of these on a whim for a bit of a play to see if I can get speed from the analogue inputs by sampling at high speed and manipulating the data. I'm not looking for big budget ideas on my track car as it's only a cheap hack for a bit of fun. The GPS isn't so much of a win for me in competition as I compete in AutoSolo, which is too low speed and twisty for GPS to really cope with (see trace). I'm going to try this non-GPS data logger to measure what I want to find (2D G-force, throttle position, air/fuel ratio, wheel speed, engine speed, brake pressure, etc.) and see if that's OK for me. If not, I'll upgrade to the DynoStar. I only really use RaceChrono when I go to the 'Ring and for straight line performance analysis. WIth the 'Ring, I'm always in a different car, so a hardwired data logger isn't practical (the car would either be my Golf or have OBD2, most likely).



Cheers,

Andy

aol_of_RaceChrono

Yeah, it's a bit tricky for a GPS if the track is too twisty, and speeds are low. But maybe some GPS data logger with integrated accelerometers would work better there. I mean one of those which use the accelerometers to improve positioning data, like RaceLogic.

Let me know if you decide to integrate a GPS with your build (shouldn't be that hard, it's "just" another RS232 input).

andylaurence

Another RS232 input would be fine if the device I'd bought supported RS232. Sadly, it doesn't, otherwise it'd be the best thing on earth! If I could find something with a decent data rate and an RS232 input, I'd get one and send you the logs. The best thing I can find is the DynoStar but that already has GPS! In reality, I will probably find the cheap data logger isn't really much use and end up buying a DynoStar. If I find something more useful, I'll let you know.



Cheers,

Andy

johntorg

Braking data doesn't seem to appear in the TrackVision .CSV export. Should it?

aol_of_RaceChrono

Currently no, as there is no braking data from OBD-II. It could be estimated from the GPS data, do you think this might be useful?

johntorg

Since Brake points are useful in analizing lap times, I think this would be very useful.