I have a customized Four Wheel Drive 1975 Volvo Wagon. It is powered by a 1997 Chevy Camaro 3.8 V6 coupled to an older 1986 Chevy S10 automatic transmission. I am also using the 1986 S10 cruise control. I made a custom reluctor ring from a motorcycle sprocket to create pulses for the stock vehicle speed sensor. This sensor sends a signal to the 1997 engine computer which sends a signal to the 1986 cruise control. I have found that the cruise control will only work up to about 35 mph. I assume there is a mismatch in that the cruise probably thinks the car is going too fast and won't engage above 35 mph. I would like to add a frequency divider circuit to cut the frequency in half or fourths. The manual says the 1997 engine computer is supposed to output 4000 pulses per mile which works out to about 66 Hz at 60mph according to my calculations. However, I have measured about 1000 Hz with my DVM while having the wheels jacked up and the speedometer indicating 40 mph. I am supplying this in case the range of the frequency is important to the design of the circuit. I believe the signal I am trying to modify is a square wave going from approximately 0 to 5V+. Can I make a circuit relatively easily to cut the frequency in half or fourths?

Brian

 

A LM4017 decade counter IC would do the job and let you divide by 1-10 pulses. Unless you have electronics experience it's going to be difficult to get done. That would be the way I solve it though.

 

Take a look at the Dakota Digital tach adapter and see if it will let you do the pulse manipulation you want...

 

From a mechanical standpoint, how about grinding, cutting, or torching every other tooth off of the sprocket? This would in effect cut the number of pulses in half. Removing additional teeth equally spaced would reduce it further. Or, decrease the diameter and number of teeth on the sprocket. Just an idea.

Dennis

 

from a mechanical standpoint this is bad....
you can get a stuck tooth(just like when you brake one off and suddenly teh gear jams) and you would get some freewheeling...which would lead to inacuraccy......

removing teeth from gears is ALWAYS a bad idea

 

it's a reluctor wheel setup,not a driven gear setup

 

I understood his post to suggest that the sprocket is only used as a reluctor ring relying on the teeth themselves (proximity) to trigger the sensor. Having a chain on the sprocket would not allow the sensor to function properly.

I do agree though, if the sprocket is used to drive anything, it is a bad idea to remove teeth.

 

If you're handy with electronics, then you could get a CMOS 4 bit counter and wire it up (with an IC voltage regulator) to divide down your frequency;
you could make up a small printed circuit board;
the counter, the regulator, and the PCB kit should be available from Radio Shack;
this is similar to what Zombie suggested above.