I have a motorcycle that I added and extra speedometer. The speed read far too low, so I bought a device called a SpeedoHealer. This thing lets you set the speed ratio to +/- about 200% of the input pulse rate. It works great. My speedo is very accurate now.

It got me wondering how they might have done that. There is a single IC that I assume is probably a PIC. There's a 2-digit LED display that displays the selected ratio and a push button switch for setting the ratio.

Any thoughts on how it works? I'm not asking for a schematic, that would be fairly simple, just an idea how the code would work.

Jack

 

What is the part number on the IC? Microchip PIC uC's all start with PIC, obviously.

They might just be letting a timer free-run at the CPU clock speed, averaging out a few samples of the clock counts between input pulses, and then using a PWM output that matches your multiply or divide requirement, or just generating that output in software.

 

Its either a simple counter (frequency divider), a special counter called a "binary rate multiplier", or a Phase Locked Loop with two counters m/n. It may be done inside a PIC, but its still one of the above

 

What is the part number on the IC?

It's been buffed off.

 

You should have got one of these;
Yellow box speedo recalibrator for motorcycles
they are more reliable than those healer ones and are a proven design with a 10 year guarantee.

 

Thanks for the ad but it won't work for me. It will correct to +100% and my speedo needed 225% since it read about 27 MPH when my GPS showed my speed as 60 MPH. I never could have gotten there with the yellow thing.

Jack

 

Another technique for accomplishing this would be to use a frequency-to-voltage converter the output of which feeds an opamp gain stage then the output of the opamp would feed a voltage-to-frequency converter. The multiplication factor would be adjusted by changing the gain of the opamp.

hgmjr

 

Sounds interesting. Any suggestions on ICs?

 

...
my speedo needed 225% since it read about 27 MPH when my GPS showed my speed as 60 MPH.
...

Sorry my mistake, I didnt realise you needed such a large correction.

What vehicle is this for? Or is it one of those kit cars?

 

I put a Harley Davidson tachometer on my Yamaha Stratoliner.

[edit] Sorry, speedometer.

 

I put a Harley Davidson speedometer on my Yamaha Stratoliner.

 

Ahh ok, thanks for the info.

You do know many of the custom Harley speedos have recalibrate function built in so you don't need a recalibrator?

Or if you must use the speedo you have, why not stick with the reclibrator you already purchased?? It's not a trivial application to make one, especially considering the speed conversion has to be accurate enough to be legal.

 

I'm using the one I bought. It just made me curious about how it works. I thought it would be fun to try to make one.

Jack

 

No more ideas on how to do this? I've been thinking about software but that seems too complicated. There MUST be a hardware chip that can do this, otherwise it must be software.

Jack

 

Here's my idea for software to do this. Count the number of pulses emitted by the VSS in a 100 ms window. Multiply that number by user's input. Send new number of pulses in a 100 ms window. repeat.

I suspect the speedometer would not mind getting pulses only half the time since half would be only 0.1 second.

Here's my flow chart.

Jack