>To find the vehicle speed for my project, I was going to tap into the >speedo wires coming from the gearbox, but after getting a wiring diagram >for the vehicle I changed my mind. It is 97 pages of schematics just for Tony, I'd suggest you persevere with the existing speedo signal. Try approaching firms who fit meters to taxis. Most cars with electronic speedos have known pickup points that people use to feed such devices. . Failing that, you could look at signals that enter the speedometer proper - there are only so many of them. I did this on one of our cars and found the correct wire fairly easily. Another alternative where there is a mechanical speedo cable is a screw on pickup that goes at the gearbox - these are made to for all common brands of car. You simply unscrew the speedo cable, screw on the pickup and then screw the speedo cable to the extension on the rear of the pickup. You can get opto and hall type pickups (possibly mechanical too). Pulses per kilometre vary with design and internal gear ratios - easy enough to calibrate by driving a set distance and seeing how many pulses you get. I have a friend who makes taxi meters who may have details on a specific car but I'll let you ask people at your end first - ask me if you are stuck and I'll email him. >I'm going to test drive the vehicle (which has a digital speedo) and >press a "button" on the controller when the speed is 64KPH. If I >multiply the accumulated speed pulse result by 64 (easy), I get the >speed at 1KPH. From then on, to get any speed in KPH, I just divide the >1KPH speed by the new capture value. Probably more accurate to find a known distance and simply count the output pulses over this distance. Of course, once you have pulses per distance the pulses per time per kph follow automatically. If you use your wheel spokes idea you could VERY accurately measure the distance travelled in one wheel revolution.(about 2 metres) (chalk tyre at bottom and ground, have person drive car slowly forwards until chalk mark does one rev, chalk ground, measure distance). You can probably do the latter to well better than 1% accuracy (1% = about 20mm in one wheel revolution). This assumes that the tyre's dynamic (road speed) size is about the same as its static size. Russell McMahon _____________________________ >From other worlds - www.easttimor.com www.sudan.com What can one man* do? Help the hungry at no cost to yourself! at http://www.thehungersite.com/ (* - or woman, child or internet enabled intelligent entity :-)) -----Original Message----- From: Tony Nixon To: PICLIST@MITVMA.MIT.EDU Date: Thursday, 9 March 2000 11:22 Subject: Speed Capture Hi all, To find the vehicle speed for my project, I was going to tap into the speedo wires coming from the gearbox, but after getting a wiring diagram for the vehicle I changed my mind. It is 97 pages of schematics just for a 4 cylinder car. That also took ages to get hold of, and I couldn't believe that the manufacturer will no longer give out any info on this type of thing. I had to get it from a friend of a friend etc. inside the business with the assurance that I was not to disclose it. -- Best regards Tony http://www.picnpoke.com mailto:sales@picnpoke.com