Speedometer question. . . number of pulses per rotation?

[ozone]

I'm trying to make my own custom automotive gauges and I found a lot of things on the internet that seem to indicate the vehicle speed sensor generates 4 pulses per revolution. I put an o-scope on it and when all was said and done, it looked more like 100 pulses per revolution, but I'm kind of wondering if I had the horizontal scale off or something.

I can retest this, but it's kind of a pain in the butt and I was wondering if anyone here knew. It's always handy to know the answer before you verify it.

This is a 1999 Solara V6 manual.

Thanks.

[gnegroni]

I'm trying to make my own custom automotive gauges and I found a lot of things on the internet that seem to indicate the vehicle speed sensor generates 4 pulses per revolution. I put an o-scope on it and when all was said and done, it looked more like 100 pulses per revolution, but I'm kind of wondering if I had the horizontal scale off or something.

I can retest this, but it's kind of a pain in the butt and I was wondering if anyone here knew. It's always handy to know the answer before you verify it.

This is a 1999 Solara V6 manual.

Thanks.

Math error?

[ozone]

I don't thinks so. I've been over it several times.

[gnegroni]

I don't thinks so. I've been over it several times.

Is it tire revolution or engine rev? At what engine or vehicle speed are you talking the inputs?

[corlon]

vehicle speed sense wire for the 1st gens reads 4000 pulses per minute. most places call this a 4-pole reading. i believe it is an AC reading and not a DC reading if that helps.

[atclate]

Do people really check their engines with oscilloscopes? Anyways, is your calculation consistent throughout the RPM ranges? I bet if you monitor it while you rev your engine up and down, you'll get a better view of the voltage of the output at different rev ranges.

Just curious, what are you using to fabricate your own gauge? Are you going to make one of those digital display with numbers? Just curious =]

[ozone]

Ok, this is a speedometer I'm talking about. It is independent of engine RPM, otherwise your speedometer would change every time you changed gears or rev'd the engine at a stop light. It is definitely a pulse that is generated by the speed sensor in the transmission which provides a certain number of pulses per revolution of the differential. This means, it must be calibrated for the tire size chosen by Toyota and will change both with tire wear and by chosing a different sized tire.

Yes, I measured with an oscilloscope because you cannot measure pulses with a multimeter (unless they are very slow). It's actually pretty cool to watch them speed up as the car is accelerated. I will post up the results later. I have them at home. I never did find out how many pulses per revolution the Solara has but I did find other cars including Toyotas that output 4 pulses per revolution. When we rolled slowly out of the driveway, I saw just a few pulses, but I have a Chinese brand PC based oscilloscope with a confusing display label and it could have set the horizontal scale to a very short time interval so that a lot of pulses looked like only a few. And who knows when I saved it if it labeled the axes correctly or not. So I need to look into how it does that to be certain.

I hate digital gauges. I plan to make my own analog gauge using stepper motors (like most quality gauges). This requires a driver, in my case a microcontroller. To use the microcontroller I have to know the nature of the signal feeding into it, hence the measurement and the question.

The repair manual told me the nature of the coolant temperature sensor, so that was easy. I measured and got something realistic for the tach reading and except for fuel there are no more gauges. For instance, the oil pressure sensor (I think) only alerts the idiot light. I would have to install a sensor that actually reads pressure. The same with a voltage gauge, etc.

When I did the calculation I got pretty close to 100 pulse/rev, which at least sounds like a nice round number. I just expected to see something like 4 pulses/rev like all those other cars. Unfortunately the manual only says that it will produce pulses, but does not say how many or at what amplitude (5 V by the way).

I took measurements at various speeds, because I wanted to see if it was twice as many pulses at 50 mph as it was at 25mph. I believe it is. I did witness a somewhat random glitch in the pulse and managed to catch it. I guess it's not enough to disturb the Speedo, because it doesn't jump or anything. Makes me wonder if the speed sensor is going bad though.

Also, I believe the 4000 pulses per minute is possibly the ability of the computer to read or something, but pulses per minute doesn't make sense because, how many pulses do you get sitting still then?

Thanks for the comments.

[corlon]

zero pulses while sitting still.

[youngblood]

I believe most if not all obd2 cars do have sensors for oil temp and pressure, so no additional sending unit should be required. My basis for this thinking is that the MSD Dashhawk can display readings for for both engine and transmission temperature as well as many others while only being connected to the vehicle through the obd2 port under the dash.

[ozone]

Thanks I'll plug in my OBDII reader and check that out. It might be that it uses essentially the same sender, but only triggers the light at a certain value. That would be cool, then I wouldn't have to get a different sender.

[Chinky420]

wow, for some reason, this is cool as hell that you know all this. good luck on the custom project

Ok, this is a speedometer I'm talking about. It is independent of engine RPM, otherwise your speedometer would change every time you changed gears or rev'd the engine at a stop light. It is definitely a pulse that is generated by the speed sensor in the transmission which provides a certain number of pulses per revolution of the differential. This means, it must be calibrated for the tire size chosen by Toyota and will change both with tire wear and by chosing a different sized tire.

Yes, I measured with an oscilloscope because you cannot measure pulses with a multimeter (unless they are very slow). It's actually pretty cool to watch them speed up as the car is accelerated. I will post up the results later. I have them at home. I never did find out how many pulses per revolution the Solara has but I did find other cars including Toyotas that output 4 pulses per revolution. When we rolled slowly out of the driveway, I saw just a few pulses, but I have a Chinese brand PC based oscilloscope with a confusing display label and it could have set the horizontal scale to a very short time interval so that a lot of pulses looked like only a few. And who knows when I saved it if it labeled the axes correctly or not. So I need to look into how it does that to be certain.

I hate digital gauges. I plan to make my own analog gauge using stepper motors (like most quality gauges). This requires a driver, in my case a microcontroller. To use the microcontroller I have to know the nature of the signal feeding into it, hence the measurement and the question.

The repair manual told me the nature of the coolant temperature sensor, so that was easy. I measured and got something realistic for the tach reading and except for fuel there are no more gauges. For instance, the oil pressure sensor (I think) only alerts the idiot light. I would have to install a sensor that actually reads pressure. The same with a voltage gauge, etc.

When I did the calculation I got pretty close to 100 pulse/rev, which at least sounds like a nice round number. I just expected to see something like 4 pulses/rev like all those other cars. Unfortunately the manual only says that it will produce pulses, but does not say how many or at what amplitude (5 V by the way).

I took measurements at various speeds, because I wanted to see if it was twice as many pulses at 50 mph as it was at 25mph. I believe it is. I did witness a somewhat random glitch in the pulse and managed to catch it. I guess it's not enough to disturb the Speedo, because it doesn't jump or anything. Makes me wonder if the speed sensor is going bad though.

Also, I believe the 4000 pulses per minute is possibly the ability of the computer to read or something, but pulses per minute doesn't make sense because, how many pulses do you get sitting still then?

Thanks for the comments.

[ozone]

Thanks. I still have a lot to learn actually. I don't really know anything about microcontrollers or how to program them, so I'm learning that too. Hopefully in a year or two I can have something that works.

Oh and by the way, it won't be in a Solara. I plan on transplanting the 1mzfe engine from a Solara into my 1988 Corolla GTS. That's the car for which the gauges would be built.

[JavaJoe_2]

I believe most if not all obd2 cars do have sensors for oil temp and pressure, so no additional sending unit should be required. My basis for this thinking is that the MSD Dashhawk can display readings for for both engine and transmission temperature as well as many others while only being connected to the vehicle through the obd2 port under the dash.

MSD DashHawk is for 2004 and up. CAN not obd2.
We don't have a trans temp sending unit. Also not an oil temp, water temp., but not oil.

[therieldeal]

could you be so kind as to post the pinout for the sending unit?

[ozone]

Check your other post for the pin outs.