Detect Signal

[angrysmileyface]

I am currently working on a project to add a second odometer to my vehicle. At this present time I believe it to be a series of pulses, however I do not know the number outputted per mile. Is it possible have the pic determine (perhaps count) these pulses initially so that I may use this number for my project? I don't believe there is a clock signal involved, and do not know the period. Any help provided is greatly appreciated. (And no this isnt a highschool or college project, I just want a second odometer for my car)

Thanks

SR

[skimask]

I am currently working on a project to add a second odometer to my vehicle. At this present time I believe it to be a series of pulses, however I do not know the number outputted per mile. Is it possible have the pic determine (perhaps count) these pulses initially so that I may use this number for my project? I don't believe there is a clock signal involved, and do not know the period. Any help provided is greatly appreciated. (And no this isnt a highschool or college project, I just want a second odometer for my car)

Thanks

SR

I assume you're talking about the digital odometers and not the old cable driven types.
On most of the dash panels I've seen, on the back, like right under the connector (a few times on the front), there's usually some writing saying something to the effect of "1320 PULSES PER MILE" ('88 Chevy Sprint). I don't remember the numbers for my other cars.

As far as calibrating (if needed), 2 methods come to mind.

-Drive 60mph, press a button, PIC counts for X amount of time or one minute, which would be perfect at 60mph since you'll also have travelled a mile, now you also have pulses per mile.

-Drive X mph, press a button when you pass a mile marker, press the button again when you press the next mile marker. Now you know how many pulses per mile (give or take). Maybe do ten miles so the 'give or take' will average out a bit.

[angrysmileyface]

Yes it's a digital signal, not cable driven. I am thinking its just tie an input pin to the signal, and do the number of pulses that show up. I need to work on some code and then we'll see if that works.

[ronsimpson]

My car gives one count per turn of the drive shaft. (output of the transition)
Multiply by the turn ratio of the rear end multiply by the tire circumference.
You just need to count how many pulses per km or mile. Build a counter with a PIC and drive for 1 mile. Every kind of car is different. You need to do the experiment.
Simple project.

[skimask]

My car gives one count per turn of the drive shaft. (output of the transition)
Multiply by the turn ratio of the rear end multiply by the tire circumference.
You just need to count how many pulses per km or mile. Build a counter with a PIC and drive for 1 mile. Every kind of car is different. You need to do the experiment.
Simple project.

Relatively simple project. I have to wonder how 'ugly' that signal will be coming off the sensor, travelling up the wire to the PIC, etc. Might have to square it off a bit with a 7404 or something along those lines so the PIC doesn't get false triggers.

[sougata]

Hi,

Most probably you would be getting a variable frequency signal. If you have access to a frequency meter (most multimeters have) then measure the frequency while driving at a fixed speed. You get an idea of the number of pulses/per second available a certain speed. Do it for other speeds as well to find if the relationship is correct. Only take care while driving and taking the reading.

[angrysmileyface]

Unfortunately I do not have a frequency meter. best I have is a cheapo Radio Snack multimeter with AC/DC, Diode test and Amperage. So I am rather stuck trying to ascertain what the signal looks like by what I have on hand. Now if I had the gear I had back in college, it would be a diff story.

Basically I think I will count the pulses that show up, unless someone has a better idea (This is a 93 honda civic btw)

[mackrackit]

Unfortunately I do not have a frequency meter.

You are building one. Be sure to look at the COUNT command in the manual. I use something similar to monitor fan and blower speeds.

A hall effect sensor is often used. If the wiring is good the signal will be "OK". The first few blade speed monitors I built used sensors from autos.