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GulleyGulley |
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#1
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Member ![]() ![]() Group: Members Posts: 67 Joined: 12-March 12 From: CNY Member No.: 14,243 Region Association: None ![]() |
Installed a 86 3.2 into my car with a tach from the donor. Everything works but the tach. It reads about double what it should. Any ideas why it's off?
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stugray |
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#2
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Advanced Member ![]() ![]() ![]() ![]() Group: Members Posts: 3,825 Joined: 17-September 09 From: Longmont, CO Member No.: 10,819 Region Association: None ![]() |
If it is of any help:
I just spent the last few weeks figuring out how the tach signal (from the coil) works and how to convert it to being read by a microcircuit. I basically used the megasquirt design to step down the 400 Volt pulse that the tach sees to something manageable to trigger a 555 timer "one shot" then the output of the 555 gets read by a arduino and the tachometer is displayed in digital numbers (Hz). Once you get the Hertz value (coil pulses per second), you then need to know if the engine is a 4 or 6 cyl, and if it has multiple spark firings per cyl firing. Then you do the math in the CPU. The same circuit could easily drive a DC motor of the type used in standard tachometers using a digital 5DC output in PWM mode. I even built an ignition mockup complete with points a coil, and a spark plug to bench test it. total in parts is about $15 and fits on a circuit board the size of a silver dollar. I know that what you are doing is different but I could lend help if needed. |
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