Reading VSS output
- Thread starter Rusty67
- Start date
nyuk98gt
15 Year Member
Rusty67:
I have a tough time with electrical stuff (missing gene or something tragic) but the VSS is alternating current so you should be able to measure AC volts (or current) on a multimeter. If it is fancy enough, it may even give RMS (root mean squared) - akin to 'average' - voltage.
I've never measured the VSS but I do know that it is an alternating current/voltage/frequency signal.
That's it, lol.
HTH,
Chris
I have a tough time with electrical stuff (missing gene or something tragic) but the VSS is alternating current so you should be able to measure AC volts (or current) on a multimeter. If it is fancy enough, it may even give RMS (root mean squared) - akin to 'average' - voltage.
I've never measured the VSS but I do know that it is an alternating current/voltage/frequency signal.
That's it, lol.
HTH,
Chris
5ubtle
Founding Member
Not easy.
Yes. Unfortunately building the converter is a job for an electrical engineer. I don't know of any converters which are marketed as "VSS to voltage". If you want to learn to make one yourself, Google "frequency to voltage converter".
Yes. Unfortunately building the converter is a job for an electrical engineer. I don't know of any converters which are marketed as "VSS to voltage". If you want to learn to make one yourself, Google "frequency to voltage converter".
wmburns
SN Certified Technician
It might help if we knew what you are trying to accomplish.
I could be wrong, but I do not think that the VSS sensor's output is voltage based. I think it is frequency based.
In any case, if you have a high end multi-meter, try the "Hz" setting. If the sensor is frequency based, the Hz will vary with the shaft speed.
I could be wrong, but I do not think that the VSS sensor's output is voltage based. I think it is frequency based.
In any case, if you have a high end multi-meter, try the "Hz" setting. If the sensor is frequency based, the Hz will vary with the shaft speed.
If you just want to see the VSS reading, I would imagine most tuning software would allow you to monitor or datalog it. I have PCMscan which is just a basic scantool/trouble shooting device and it can datalog VSS, along with pretty much every other drivetrain sensor
I'm going to be puting a T56 into my car and it has that reverse lockout solinoid on it. I wanted to build a box that I could wire in that would disable the reverse lockout when the car is under 5 MPH just like the stock Cobra ECU does.
For now I have used a spare fog light switch with a relay but this is a bad solution because I tend to forget to turn it off. I still want to build the box. I have a fairly good idea what I need but I just need a tiny bit of help from someone who is either a good EE or has the experience to clue me in on the piece of the puzzle I'm missing.
wmburns
SN Certified Technician
Sooooo. Have you tried measuring the VSS output with a DVM? Pay attention to the frequency (not the volts).
There is a write up in the Ford Service manual regarding the priciples of operation and how to trouble shoot the VSS sensor. Seems like a great place to start for information. PM if interested.
There is a write up in the Ford Service manual regarding the priciples of operation and how to trouble shoot the VSS sensor. Seems like a great place to start for information. PM if interested.
nyuk98gt
15 Year Member
Rusty67:
Check out accutach.com (Mark Olson's site). He know just about everything there is to know about VSS and OSS signals and may be able to assist with what you are doing. (Actually, he has exactly what you're looking for!)
Chris
Check out accutach.com (Mark Olson's site). He know just about everything there is to know about VSS and OSS signals and may be able to assist with what you are doing. (Actually, he has exactly what you're looking for!)
Chris
nyuk98gt, I've been to his site. He actually sells a product that disables the lockout for a short time period using a momentary push button switch and a timer ciruit. I didn't really think asking him for help would get me any where since I am making something he would provably see as a competing product.
On a side note.... His accurate gauge conversion is really something I would love to have, I have never liked how the stock gauges don't really tell you anything unless there is something seriously wrong. If he releases that for the 99-04 I'll be jumping on that quickly.
On a side note.... His accurate gauge conversion is really something I would love to have, I have never liked how the stock gauges don't really tell you anything unless there is something seriously wrong. If he releases that for the 99-04 I'll be jumping on that quickly.
trinity_gt
10 Year Member
For a variable-reluctance speed sensor I'd probably suggest considering something in the MAX9924 series of integrated circuits to parallel-tap the VSS wires to obtain a clean, logic-level frequency output. You then have a couple of options:
First you could use a purely analog approach using, say, a frequency-to-voltage converter and a comparator to trip a relay when the frequency (and thus vehicle speed) moves above a certain threshold.
Second, you could consider a small microcontroller to measure frequency directly and control the relay. As a digital designer I tend to favor the microcontroller approach because it allows you to easily do things like hysteresis (e.g. enable the reverse lock out at 6 MPH but don't re-enable is until, say, 3MPH is shown...) and is generally less finicky than purely analog approaches.
Needless to say, unless there's already a box out there (hint) you're going to be looking into a bit of engineering...
First you could use a purely analog approach using, say, a frequency-to-voltage converter and a comparator to trip a relay when the frequency (and thus vehicle speed) moves above a certain threshold.
Second, you could consider a small microcontroller to measure frequency directly and control the relay. As a digital designer I tend to favor the microcontroller approach because it allows you to easily do things like hysteresis (e.g. enable the reverse lock out at 6 MPH but don't re-enable is until, say, 3MPH is shown...) and is generally less finicky than purely analog approaches.
Needless to say, unless there's already a box out there (hint) you're going to be looking into a bit of engineering...
trinity, I already know about the box from samco but I wanted to build something and then put it out on the internet so that anyone comfortable enough with a soldering iron and relays could built it on their own.
I haven't looked at the max9924. I think I was looking at an LM2907. I was going to try doing exactly what your first sugestions is where I provied a reference voltage to a comparator which would operate a relay. I'm not an EE but I do have a friend who is one. He hasn't been much help... he claims we need an oscope to do this but I'm wondering if that is the case or not. My lack of EE skills makes it hard to tell if he is clueless or if what I'm trying to do is a bit harder then I think it is.
Thank you for your sugestions, I will look at the max9924.
I haven't looked at the max9924. I think I was looking at an LM2907. I was going to try doing exactly what your first sugestions is where I provied a reference voltage to a comparator which would operate a relay. I'm not an EE but I do have a friend who is one. He hasn't been much help... he claims we need an oscope to do this but I'm wondering if that is the case or not. My lack of EE skills makes it hard to tell if he is clueless or if what I'm trying to do is a bit harder then I think it is.
Thank you for your sugestions, I will look at the max9924.
trinity_gt
10 Year Member
The MAX9924 (or something like it) will provide a convenient high-impedance front end to your circuit that won't interfere with the operation of the PCM in reading the VSS. Because a VSS is a magnetic device its output will (a) be AC, (b) increase in amplitude with increasing speed and (c) increase in frequency with speed. It'd be nice to have a single piece of silicon do that side of the interface, giving you a nice logic level pulse train to work with.
Interesting reading for a 94-98 VSS:
http://accutach.com/Documents/VSSCharacterization.pdf
Depending on the style of sensor you're interfacing to (gear-driven like earlier units or magnetic pickup as later units were) you might want to do a bit of probing to calibrate your system.
Interesting reading for a 94-98 VSS:
http://accutach.com/Documents/VSSCharacterization.pdf
Depending on the style of sensor you're interfacing to (gear-driven like earlier units or magnetic pickup as later units were) you might want to do a bit of probing to calibrate your system.
nyuk98gt
15 Year Member
Rusty67:
Yes, if you're making a competing product, then Mr. Olson may not be keen on chatting with you about his stuff. I thought you were just doing this for your vehicle and, in that case, I am sure Mr. O would assist.
GL with your "black box"!
Chris
Yes, if you're making a competing product, then Mr. Olson may not be keen on chatting with you about his stuff. I thought you were just doing this for your vehicle and, in that case, I am sure Mr. O would assist.
GL with your "black box"!
Chris
trinity, if only I have a 94-98 Mustang, the last line of that PDF would be the answer I was looking for. The OSS on the 99+ outputs at a different rate. I'm sure if it would convert or not. Sadly, I need to shelf this project for the next 3 weeks. Thanks for the new info guys. I will report back later if I make any head way.
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