Hello everyone,

Before I ask for assistance, I would like to tell everyone that I used the search function and looked for speedometer and read every forum on on this subject before asking my question.

Ok, now I would like to build a digital speedometer using this schematic http://www.edn.com/article/CA529384.html

The only difference is that I will be using the cars VSS instead of the Hall-Effect Sensor.
The only question I have is, the Above schematic is configured for km/h, I would like to use mp/h. So how can i achieve this and what do I need to do.

Any help would be great,
Thank You for your time.
Danny - argenstyle

 

It depends on the output of the VSS (vehicle speed sensor?). If it's compatible, then it can make a reasonable input.

One thing to determine is the number of pulses per revolution. If it's different from the Hall effect pickup, then the program will have to be changed to accomodate that. Changing to MPH is another program change. One kilometer is about .62 miles. Or you can figure it frm the exact equivalence of 2.54 cm = 1 inch.

 

Thanks for the info:
I will need to find out the VSS output on my car, I believe its 4000 pules per mile. The km/h is not a big nuisance, I guess I will build it first and then work from there.

If anyone else has anything to add, please do. I am open to an ideas that will help me build this device or improve on its design.

Thanks...

 

I also am looking for info for the VSS, so if you find anything definite, please post it here. I'll do the same.

My current understanding is that the VSS pulses 4x per rotation of the driveshaft. However, I havent found anything definite yet. OTOH, it would make more sense for a fixed pulserate per rotation of drive shaft vs fixed pulserate per distance.

 

What car do you have or what car VSS are you going to work with, Cause I know different cars use different VSS rates.

 

Uh, yeah. The distance is dependent on the tire diameter. This is only known if you're using the recommended tires at the recommended inflation. At the calibrated wear situation.

 

You could code up a "calibration mode".For instance:
1.Enter mode
2.Roll the vehicle a certain distance (like 1 foot or some other easy to calculate distance)
3.Count the pulses to roll that distance.
4.Do a little math

 

My target vehicle right now is a 2007 Ford Crown Victoria.