> Does anyone has any experience tapping signals from the tachometer? Is there > any other method of knowing a car revolution per minute (rpm)? > > I was thinking of designing some simple module with a uC that interprets an > automobile rpm and do certain things accordingly, for example, locking of > door and sounding the buzzer when the hand brake is not released, etc. > > I don't have a car of my own, as such, can anyone describe the expected > waveforms roughly? Can we actually tap the signal and feed it to a ADC or a > Timer input Capture, simply? We did a project that controlled the speed of a gasoline engine. The engine speed feedback came in the form of tachometer pulses. This was for a marine engine, so the tachometer signal "standard" may be quite different than for a car. In this case the tachometer signal was actually right from an alternator output winding. Of course it varied greatly in amplitude with speed. Some analog circuitry filtered it and converted it into one digital pulse per cycle, which was fed into a CCP input of a 16F876. CCP modules in capture mode are great for measuring the period, which was inverted by the firmware into speed. In really old cars the tachometer signal was actually a rotating flexible shaft. My 1972 Pinto had one of those, but you would probably have trouble finding this if you wanted to. On some cars I've seen magnets on the drive shaft with a pickup for the cruise control, but the tachometer seemed to be driven from elsewhere. I'm guessing that newer cars have a more integrated approach, but I don't really know. I've been out of touch with these things ever since my 1984 Escort finally died. That was the last car I had chance of doing things myself on. After that, everything is controlled from one unfixable enigmatic computer module. On the other, I haven't needed to mess with my 1996 Neon. It must be all the tecnolergy in it . ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu