Setting up different divisors in something like an Arduino to show correct vehicle speed regardless of which rear gear would be pretty easy.
I'm currently using an Arduino based speedo in my car, just driving an LCD currently, but plan to have it drive a motor to drive the original speedo eventually. It wouldn't be that difficult to have the code check a digital input to swap between two divisors used in the speed calc to get proper vehicle speed.
The man who says something is impossible, is usually interrupted by the man doing it.
I agree. I'm thinking it would really fun to try and retrofit the steppers they use in modern clusters. Keep the outside look and feel of the original gauges, but modern steppers behind them. Easy for something like an Arduino or Microchip Pic...Originally Posted by Six_Shooter
I've never seen a DRAC/VSSB connector layout with a 40ppm output shown. I think you're looking at 2 different 2000ppm configurations depending on the module and/or the mask.
I would agree with Dave, you can't use a DRAC in a newer truck because the DRAC is missing the correct output for the anti-lock.
With a 2-speed rear-end you could use 2 different DRAC modules and switch between them.
Last edited by lionelhutz; 12-10-2016 at 06:56 AM.
My bench (and in car) testing shows otherwise.
Pin 13 of the VSSB is indeed a 40 PPR output, it follows EXACTLY what the input is doing, but a 5V square wave instead of a VR signal. I have verified this on my bench with an oscilloscope, and in car testing where I was originally using the Arduino based speedo directly to the VSS wire, but am now using the VSSB to drive that signal, and the speedo is reading the same. Any other output (2000 or 4000 PPM) reads significantly lower. I never tried the ABS connection as it is much higher than I need.
Dave W's pictures in post #8 verify what I've been talking about, pin 13 is labeled as 40 PPR, and in one of the other pictures it shows this connected to pin F12 of the PCM.
The following 3 schematics also show this, really one large schematic, just broken into 3 parts for clarity.
Switching between 2 VSSBs could work, as long as the gear ratio change falls within the adjustable range. For that matter going a bit deeper, you could set up some a small circuit (based on some transistors and/or relays) to switch between the two settings where the jumpers where normally go.
The man who says something is impossible, is usually interrupted by the man doing it.
Interesting. I'll have to look into this. It's my impression from the reading I've done so far the 4x4's with the 4L60e/4L80e have the driveshaft VSS moved to the transfer case so what the PCM and speedometer sees is revolutions of the drive shaft. The ratio change in a 2-speed rear happens after this sensor. I will try and understand more about this "4low" setting.
My plan is to adapt the entire non-anti-lock braking system from the Ford F550 for this project (similar class 4 vehicle). No anti-lock for this truck means that kind of output from the DRAC/VSSB wouldn't be needed. Your idea to use two DRAC/VSSB's for the ratio change is also interesting. I'm imagining though it might take a fair bit of steering logic to do this. Might be easier to make a device out of a microprocessor that emulates a DRAC/VSSB instead. Then in software I could change the divisor by simply changing the state on an input pin when I make the gear change.
All worth looking at!
David
Oh I like that idea! Use one DRAC/VSSB, but put the steering logic at the jumpers... Very cool. Relays might be the safest because of an earlier post I saw from Mark about how his experiences with dip-switches seemed to fail for him. Even a tiny relay would handle much higher currents.
FWIW, I've had zero problems using dip switches on several DRACs/VSSBs.
The man who says something is impossible, is usually interrupted by the man doing it.
I wonder why Mark had problems? If I find that thread, I will link to it...
Managed to pick up a couple of VSSB's:
My plan is to add dip switches to one DRAC (7 jumpers) and one VSSB (14 jumpers). I'll then power them up on the bench, feed them a sine wave signal to simulate the output of the VSS signal, and look at ALL the outputs with a scope. I'm assuming the VSS is some kind of hall effect sensor that outputs a sine wave centered around zero volts:
I'll set the dips to a known tire diameter and differential ratio, and using a couple of counters see if the ratio of input pulses to number of output pulses (2,000?) per mile makes any sense. Still not 100% sure I know what I'm talking about...
I will report back with my findings when I get some more free time.
David
Last edited by DavidBraley; 12-30-2016 at 12:35 PM.
David, just to clarify a couple of things. The VSS in this application is whats known as a Variable Reluctance sensor which produces an AC, analog voltage. This voltage will typically vary between 10s of millivolts, to around 100v at speed. The DRAC/VSSB inputs this analog signal, and using a hysteresis, output an equivalent digital signal ranging from 0vdc to ~5vdc.A double pole relay would be simple, but so would a 3-way toggle to switch between buffer modules. Just a thought.P.S."buffer" is a generic term used to convey a conversion of sorts within the module.Bud
If it don't fit force it, if it don't force fit f&%@ it!
Thank you for that information! Because my electronic skills are the least developed (I still manage to let the magic smoke out of stuff...), I would like to try and verify the output for myself as well. I need the practice!
I bought a 40 tooth reluctor ring out of a 4L60e on ebay yesterday and it's on it's way. My plan is to chuck it in the lathe, and use one of the VSS's out of the 4L80e I have here to measure the real output. I will also take some careful measurements to determine the gap between the VSS and 40 tooth ring. If my setup on the lathe is robust enough, I might just use the output from the VSS as the actual input to the DRAC's/VSSB's for my testing. Using a large lathe should make the most expensive and massive signal generator EVER! LOL! I will report back here with everything I learn...
Last edited by DavidBraley; 12-28-2016 at 08:10 AM.
The input to the DRAC is typically a sinusoidal signal with no or very low offset. Usual test the waveform I use on my function generator when driving a DRAC/VSSB. Though I have found that square waves work as well.
Last edited by Six_Shooter; 01-03-2017 at 06:41 AM.
The man who says something is impossible, is usually interrupted by the man doing it.
4L80-E OSS reluctor is actually the park lugs on the rear carrier, having 40 lugs or teeth same as the 4L60E. The DRAC can take a digital pulse as well.
If it don't fit force it, if it don't force fit f&%@ it!
Bits for testing are starting to get here...
Hello, I've been reading with interest this post on VSSB/DRAC. I have 1995 S10 running gear in a 76 Chevy LUV Pickup. I have a EFI 4.3 with a 5 speed manual transmission. I have a electronic speedometer I am having trouble making work. Because I don't have ABS or an automatic can I bypass the DRAC and just run the signal from the VSS directly to the speedometer?
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