
Controlling a motorcycle tachometer with a Raspberry Pi - xylon
http://www.naughtycomputer.uk/controlling_tachometer.html
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kevin_thibedeau
Sort of a a circuitous way to drive a device that's ready to take a pulsed
frequency input without tearing it apart. Should have tried harder to figure
out how to do it in FreeBSD or just dump the OS and baremetal it.

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lutorm
I agree with circuitous. Most tachometers just take a pulse train from the
ignition, so all you need to do is vary the pulse frequency instead of the
pulse width.

On my Honda NC30 project bike, I'm feeding the stock tachometer with a
variable-frequency pulse train from an Atmega328. The tacho just wants its
input pulled to ground with a frequency equal to 4x the RPM, so one external
transistor is all that's needed.

(The 328's main function is for talking to the wideband O2 sensors and sending
that data over the CAN bus to a Microsquirt ECU, but it works nicely for also
reading engine RPM over CAN and outputting the signal to the tacho.)

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randlet
You made the front page of HN... Hope you've got a rev limiter installed by
tomorrow!

