Pulse Modulation

Hey guys,

This is my first post here! I did do a quick search but couldnt find anything that helped so I figured I would post up. As a warning, I am totally ignorant in the knowledge of what goes into the making of small electronics. I'm a quick learner and understand the basic properities of most parts; I just don't know how to put it all together.

My project goal is to correct the speed displayed on my motorcycle speedometer.

To accomplish this I will need to create something that will modify the input signal coming in from the speedo sensor into an increased or decreased pulse to adjust the speedometer.

My understanding of the speedo sensor is that it is based off a magnet going over a speed ring mounted on the wheel. Because of the magnet goes over this ring (which alternates between a metal piece then a space then back to metal, etc) in this fashion, it is my understanding this would create a pulse of sorts in the two wires coming from the sensor.

In my mind this project just seems very easy but the most I have done is spliced wires together or put together preassembled computer parts. So I dont really know how easy/hard a project like this is.

Any help will be appreciated as it will help me learn to do a new hobby!
puma

So does your motorcycle have an electronic speedometer that reads wrong? Or is it a mechanical one, and you want to add an electronic one?

Try going over to "Search" on this site and search for "speedometer". I get 98 hits; you should be able to find something that should at least get you started. Then you can come back and ask some better questions.

If it's like the speedo on BMW K-bikes, it's a magnetic sensor issuing pulses from the rear wheel. The display is a simple dial, but is really a voltmeter. The key is that the pulses are integrated by an opamp; taking the pulse train and accumulating/averaging it into a voltage.

Given manufacturing variances, there is a trim pot to set the opamps' gain. That's how BMW did it on all K-bikes and sets the calibration.

If it's a digital display; unless it's Really off, you'll probably have to live with it. Calibrating a digital entails remapping the pulses/sec -> display value, stuff embedded in the instrument controller. By the time you figure out how to do that, you've built your own instrument Several times over. I've built 3 instrument clusters for K-bikes, you just Can't get access to anybodys' embedded code (other than your own).