Subpage of MembersPage/MarcellGal/PowerAndTraction
I plugged in [PS2 wheelspeed cable] to the PS2 connector of my old 3B ECU with (using 2 wires: pin2,3 of 3pin injector connector for the audi transmission side)
- it just works. Need to calibrate for correct kp/h value though.
Making small vemstune ini change so the descriptor is available (under the GPS group, although this comes from ECU, not from GPS).
Anyone knows the correct setting for the speedsensor calibration for kp/h (I have factory tires on 15" rims) ? Or the number of pulses per wheelrot ? 8 or 9 ?
- since 100 km/h = 27.8 m/s
- If wheel circumference is 2m, and 8 pulses per wheel rotation, than 1 pulse = 2m/8 = 0.25m
- so configuration in vemstune 27.8/ 0.25 = 111 (Hz / 100)
With GPS hooked up to notebook, (and configured in VemsTune) the GPS is sometimes higher, sometimes a bit lower than the wheelspeed (GPS lags a bit behind). Will need to get this (and gear calibration) straight on clear roads.
It would be much easier to mount a round device and display precisely calibrated digital wheelspeed on it, than sorting out this mess around the speedo gauge in the dash.
I'm also thinking of lighting up a "stayaway" light (different color than the red shiftlight) in the speed ranges:
- 72..75 km/h (with limit=50km/h they pull your licence above 75km/h)
- 86..90 km/h (with limit=60km/h they pull your licence above 90km/h)
- 100..105 km/h (with limit=70km/h they pull your licence above 105km/h)
- 114..120 km/h (with limit=80km/h they pull your licence above 120km/h)
- 128..133 km/h (with limit=100km/h they pull your licence above 133km/h)
- 161..172 km/h (with limit=130km/h they pull your licence above 172km/h)
This would help prevent serious speeding while allowing some slight speeding.
I found the connector that should go to the transmission speedo output (we already have the backup lights hooked up properly and working ;-)
The 3pin female connector has
- pin1 black-blue +12V (when ignition is on, fuse-relay panel pin B15A fuse#12) supply for HALL sensor
- pin2 brown-red pulled up by the car with 100 Ohm (strong pullup!)
- pin3 brown: GND
My 6 gear audi transmission sensor seems to have a simple reed-switch between pin2-3. It's a passive device, does not need supply on pin1 (with the [PS2 wheelspeed cable] I did not connect any supply).
This matches the [fig09.pdf instrument panel schematic] perfectly.
- the outer housing (shell) of the 3pin female connector is broken off, the inner part keeps the 3 receptacles together but does not guarantee perfect mating (also, one has to be carful with the direction!)
- when I pushed the connector on, and drove around with the car, there was some speedometer needle activity. It was fluctuating, not stable at all, which I blamed on the half-broken connector... but something else might be broken here, read below...
The speedo sender in the transmission
- only has 2 pins in the 3 pin connector. Pin1 is missing.
- it seems to be a reed-relay (same type as in your bicycle speedometer), that does not need +12V supply. Obviously the same harness is used for older (or other) sensors that have HALL sensor inside, these do need the +12V supply
- when pushing the car around (in neutral gear), the Ohm-measurement between the 2 pins flip from near 0 Ohm (1..2 Ohm) to near infinity (>2Mohm)
- that's what you expect from a reed-relay
- it seems to give more than one pulse per wheel rotation. One is a bit reluctant to do this measurement properly when pushing 1500kg back and forth. From some internet page (todo: find again) I remember 1670 pulses per mile (isn't that the ABS sensors ? No, the ABS must be much more, sg. like 20..100 pulses per wheel-rotation). 225/60 R16 tyre circumference is (16*25.4 + 225 * 0.6 * 2) * pi = 2125 mm (is this correct?). 2 pulses per wheel rotation would be 1600 / 2.125 *2 = 1506 pulses per mile ... more measurments needed to find out the truth
- duty is obviously much "higher" than 50% (the resistance is 0 most of the time, rarely infinite - obviously infinite when the magnet is close)
Maybe I have to hire a car-electrician to disassemble the instrument cluster, and do what [SJM] suggests. I've seen Scrambled Auto Check "OK" display recently, which is another symptom of instrument cluster solder-over-wear (Flash Gordon was there in silver underware).
Frequency signal to the brown-red pin2
- generated wav file with ElectronicDesign/TriggerSignalGenerator, using c004 100-100-100-100-200-200-200-200-300-300-300-300-.... 7800
- using a recent signalgen, the secondary trigger pulse was 50% duty. Earlier, it was narrow. I look at the wavfile (and play them) in audacity (a nice program, works in linux and windows)
- the secondary trigger output (notebook soundcard 3.5mm jack speaker output, right channel) was connected through 1kOhm to the base of a small NPN transistor (BC817 sot23, but almost any type should work), the base was also pulled up via 10k to +5V (this should not be necessary as the soundcard output is several Volts, opens the transistor easily)
- the NPN output was directly connected to the brown-red pin2
- without wav-file played, I measured appr 7.8V DC voltage
- with wav-file played, I measured appr 3.9V DC voltage (makes sense, if the NPN pulls down the signal to 0V 50% of the time)
- To my surprise, the speedometer needle didn't move away from the resting 20km/h
- no, I didn't forget to have ignition on
- maybe it's sensitive to the duty of the input signal ?