I am trying to interpret the serial pulse train output of an Audi automotive accelerator pedal. I need to convert the pulse output into a linear DC voltage corresponding to a range of pedal motion from idle to Wide Open Throttle. A file depicting the pulse output from the pedal at idle and WOT utilizing LabVIEW is attached. Thank you in advance for any help!
Those are very strange signals! You describe them as serial pulse train signals, but they certainly do not look like TTL pulses. Also, if you removed the labels "Idle" and "WOT" and showed me these two pictures, I'd be hard-pressed to "guess" that one represented a "minimum", the other a "maximum", and to tell which was which. That being the case, I think you have a problem (in solving your problem, that is) ...
Where are you trying to take this reading from? As far as I am aware the throttle position sensor IS a voltage output. If you have access to a VAGCOM, you should be able to monitor this signal directly.
All pedals I have testes over the years have been voltage ouput! These Audi vehicles, A5 and Q7 are unique! I have an actual pedal on the bench, it was too difficult to test in the vehicle under the dash, where we normally access the signals directly from the pedal, in that I needed to utilized more than just a voltmeter and investigate the actual signals. Our LabVIEW test system utiizing compact DAQ is setup to monitor a DC voltage directly from the accelerator pedal to determine accelerator pedal position. To our surprise, there was no DC voltage! Please refer to attachment which describes pinout of the Audi accelerator pedal P/N 8W1723523. I also included two bmp files from a Tektronix scope.
Could be signals transmitted via SENT protocols: https://en.wikipedia.org/wiki/SENT_(protocol). It seems like sensor signals are trending this way. If it is really SENT, there is LV SENT driver API you can use: http://sine.ni.com/nips/cds/view/p/lang/en/nid/211171.
I think Renato_Yapaulo is probably right, namely you are looking at a digitally-transmitted one-wire serial stream, quite possibly using the SENT Protocol (which calls for 8 data intervals following a "synch" pulse -- I'm not using the correct terminology here, but this is the pattern that you show in your first PNG). The "information" is in the timing of the 8 pulse pattern, not in their amplitude. You should also be seeing nice (sharp) TTL pulses, not the peaky signals you show, but those could be due to measuring them with something that loads the signal. I'd advise following up on Renato's suggestions ...
Wow! This is too Kool. Never heard of such a protocol! I don't think they had such a thing in the 70's in my electronic engineering classses? I'll definitely delve into this. Thanks so much!
Thanks for the LabVIEW SENT API, however it is only valid with FPGA, unfortunately I'm utilizing cDAQ with embedded windows 7. I'm hoping to be able to find or build a hardware interface if it's possible for me to actually interpret the signal. I don't have a transmission spec sheet.
I wonder if the serial pulse transmission spec would be listed in an Audi Service Shop Manual?