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Subpage of MembersPage/MarcellGal/PowerAndTraction 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. 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. ---- '''[http://www.sjmautotechnik.com/trouble_shooting/instrument.html#speedo Speedometer]''' 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 This matches the [http://www.autolib.diakom.ru/CAR/Audi/1989/200/WIRING DIAGRAMS/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 [http://www.sjmautotechnik.com/trouble_shooting/instrument.html#speedo 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 ?
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