Need help from electronics wizard please

[mechman600]

Basically, I want to turn a circuit on when my vehicle reaches a certain speed. So, what circuit do I need to build to take the signal from my VSS signal wires and once the frequency reaches a certain speed close a circuit?

I am messing around with my TC lockup. Typical ford lockups: lock-unlock-lock-unlock-lock-unlock.....all with the very slightest throttle movement. I want to "fix" this.

Thanks in advance.

[saand]

Hi Mechman,
I am sure there are many ways to do this but with a quick search on voltage to frequency converters i found this chip which will do what you want
LM2917 - Frequency to Voltage Converter

on page 8 it even has a circuit for a speed switch so it looks like exactly what your after.

good luck

[mechman600]

Awesome. Thanks!

Page 8 contains exactly what I'm talking about. How would I control/adjust what frequency is required? By a variable resistor on pin 3? And what size of capacitor would I use on pin 2 & 3, or do I just go by picture above it?

[saand]

There is a little writing above the diagram on page 8 that has
load is energized when f>1/(2*R*C)
So set your resistor and capacitor appropriately and you should be fine.
If you choose a set capacitance then you can use a variable resistor to change the speed at which the TC will lock using the resistor.

So i dont know the frequencies you will be looking at but say you have a 1 uF capacitor and a variable resistor that goes between 0 and 500kohm you will get a frequency selection between infinite and 10Hz. You will not get very good accuracy if the frequency is too high with these R and C values.
I suggest playing around with the numbers and see what you get, you can always change the R and C later on if it doesn't work for you as well.

[mechman600]

Awesome.