AP60B Needs Higher VSS Frequency

I have installed a Command Ap60B on a Mitsubishi Delica.
I have used the VSS output connection that is on the back of the instrument panel.
It works fine but the lowest speed it works at is 50kph.
There are now many many 40 zones everywhere.
I need the CC to work at 40kph to minimize my donation rate to the police.
There are a few jumper-links on the AP60B circuit board to assist matching the VSS output to the AP60B.
Unfortunately these affect the higher speeds as well.
There is only one setting that will allow the CC to work at 40 kph but with this setting the cc will not function above 80 kph.
I need to double the frequency from the VSS and feed this to the CC.
The vss output is not a square wave, its rectangular. If it was square the solution is very very easy. BUT its not.
So does any one know how to increase the frequency of the VSS output while preserving the duty cycle (signal shape)?
Dakota Digital do have a device to do this, but I have no idea how it works.

Thanks in advance

I'm not sure what you mean by "rectangular". Are you saying that the frequency is always the same but the duty cycle is changing to reflect speed? If the Ap60B is reading the frequency at all I would think that there would be a frequency component to it.

What is the frequency of the VSS at 50kph? 25kph? 75kph? What is the duty cycle at these speeds?

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Kevin Pierson

A square wave has a 50% duty cycle. A rectangular wave has a duty cycle between 0% and 100%.
The VSS signal here is about 20%. Basically a pulse followed an interval with the interval significantly longer than the pulse.
The AP60B operates on frequency.
The duty cycle does not change.

There are many easy ways to double the frequency of a 50% duty cycle square wave.
Easy to find circuits for this as microprocessor clock speeds need to be changed.
Data clocks are 50% duty cycle.
These methods do not work correctly when the duty cycle is not 50%.
The case here 20%, the output becomes 2 pulses and a long interval.
The cruise control sees this as garbage.

All resolved now with 2 circuits.
First convert the VSS to 50% duty cycle and then double the frequency via the simple methods above.