Controlling a motorcycle tachometer with a Raspberry Pi

naughtycomputer.uk

20 pointsxylon4 comments

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.

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.)

Doesn't the RPI have a backlight dimming PWM as part of the default board setup?

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

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