RPM Signal Generation Help

[Mark Walker]

Hey Guys and Gals,

We have a little project we need to get the bottom of that could use the help of our most electronically knowledgable hackspacers.

We have a dashboard off of a radical trackcar that seems to have a problem detecting the RPM of the engine when connected.

The below link in which the dash is used by someone else as a project mentions him using a signal generator to simulate an engine rpm signal:

http://radovan.me/Dashboard-controller.html

As we dont know if the rpm detection works at all it would be really useful if someone handy with a signal generator could show/help us determine if the dashboard we have has an issue or whether it is genuniely an issue with layer one somewhere on the vehicle.

So could anyone be available on this wednesdays open night to help?

Cheers,

Mark

[Greg Fenton]

Depending on the system RPMs are a voltage that is always off apart from a brief period  once per revolution or always on apart from a brief period once per revolution.

Imagine a disk with a small hole drilled near the outer edge, an LED under the disk and a light sensor above the disk.
Turning the disk will let the LED shine through the hole once per revolution.
Start a timer running then wait until the next time the light sensor is triggered.
You now have a time period, a little basic maths would take that time and convert it to RPMs.
If the time taken between pulses was 1 second we could use 60/1 which would give us 60 RPMs.
If it was 0.5 seconds then 60/0.5 would give us 120RPM, 2 seconds per revolution 60/2=30RPMs.

Hope that helps

Greg, Newcastle Maker Space and former West Midlands bod