For any add-on boards such as VR conditioners, optos and OEM interface boards
#49169
I do apologize that my first post is a cry for help. HELP!!!!

I have designed and built (just at final assembly) a custom dash cluster for a classic Mustang. More details on that another day. . . . but it uses the following:

1/ An ESP32 for main processing. Directly runs 4 servo gauges, all the sensor inputs, OLED (I2C), 2 rotary encoder knobs and WS2811 LED's
2/ Arduino Nano for the tach (RPM). Runs a x27 stepper motor needle for speedo gauge, outputs rpm etc to the ESP via I2C. Receives its RPM signal direct from the Engine ECU.
3/ Aruidno Nano for the speedo. All exactly as the RPM but takes an input from a VR conditioner which is connected to a wheel ABS sensor.

The very last step was to get the signal sorted for the speedo signal. i.e. a road speed pulse signal input into the speedo Nano.

As I have also built custom suspension, which uses Mazda RX8 hubs, I have ABS sensors which are otherwise spare (not bothering with ABS. Don't need it - the car only has 500hp :lol: ).

I tested the ABS sensors with an Oscilloscope and get a nice clean VR signal: a wave type signal (i.e. not square pulse) 48 times per wheel revolution. This signal increases in size (voltage) the faster the wheel spins, and together with only having 2 wires I decided this must be a VR sensor. At slow speed (9htz) I get circa 50mv. This increases to around 2v at the fastest speed I can spin the wheel. 1000htz would be 101mph with the tyres I have fitted and 48 pulses per revolution.

To adapt this signal to the Arduino Nano I purchased a DSC VR Conditioner from DIY-EFI.co.uk site (I am in the UK) (link below).

https://diy-efi.co.uk/product/speeduino ... onditioner

I soldered it all in and if I touch the end of the cable the VR1 light indicates. Tapping the end of the wire fast gives me speedo movement (around 10mph is the quickest I can tap it). So I know it is all connected and basically working.

But when connected to the wheel sensor, I have nothing. Nada. Dead. Regardless of how I connect it, how fast I spin the wheel etc, there is nothing triggering the DSC (no light) and nothing output to the Nano.

Please help. What am I missing?

I could interconnect to the VSS (vehicle speed sensor) fitted to the transmission (standard Ford AOD) but that is also a 2 wire VR sensor so likely won't be any different.

Have I purchased the wrong type of conditioner (i.e. not sensitive enough) or connected it wrong?

I have tested it with the shielded twisted 2 core cable but also directly connecting the sensor to the DSC (basically directly). So it is not a signal loose issue. The shielding is earthed one end. The two twisted cores carry the VR signal.

Any help appreciated please.


To summarize I have:

- The two VR sensor wires connected directly to VR1+ and VR1- inputs of the DSC VR conditioner (tried switching them, makes no difference).
- VR1 Output connected to Nano.
- 5v and GRD connected obviously.

Works when I tap the VR+ input if I have my other hand on a voltage+


HELP! and THANK YOU!!!

Mick
User avatar
By PSIG
#49173
With those basic connections, the DSC should operate, if the signal voltage is high enough. The DSC was intended for typical crankshaft sensors, with typical trigger wheel rpms of 200 and up. That said, it can trigger at very low rpm if signal conditions are suitable, such as the video test below. I would verify the VR signal is suitable.

I am about as confused as you at this point, and I'm thinking something simple, such as connection to the sensor shield wire rather than the signal wire? Or, the signal voltage is too low? Or, the VR internal resistance is too low or high? Or, the alignment and spacing to the trigger wheel is too small or large? Something simple like that could be defeating the signal.

Do you have a 'scope image of the spinning wheel VR signal? Try it disconnected and connected at the DSC inputs, which may give more clues. Also trying it with sensor-out and triggered manually with an object could tell us if the output is sufficient otherwise. Note there are limitations for the signal with any conditioning circuit, and for example the common MAX99xx series has a lower limit of 120-160mV.

https://i.imgur.com/SpyP36R.mp4
#49175
I really appreciate your input (no pun intended). Thank you.

I have since tried the exact setup using the signal from the VSS and it works perfectly. Absolutely perfectly. So you guessed it, I will get the signal from the VSS and give up on the ABS.

I think you hit the nail on the head. The voltage from the ABS was definitely small. 20-50mV from memory (will test tomorrow) and as it works so well on the VSS it must have a high and more suitable output.

I did a load of sums and have calibrated my readouts/dials/figures accordingly and the VSS gives me a steady signal as low as 1mph. So I am very happy with that.

The VSS is intended to signal the main ECU. No idea why as the AOD is not an electronic transmission. :? Cruise control?
Emissions? :?

So I just hope that the ECU won't mind me piggy-backing off the VSS signal.

Thanks for the help. I may have a play one day with the ABS. Shame I can't use them as 4 spare unused ABS sensors seems a waste. :mrgreen:
#49177
ABS is some quite serious stuff and the manufacturers do nothing by chance. You seem to have a real mismatch sensor/ electronic wise. The ABS rotors are usually build much lighter than the huge teeth of an engine VR wheel. So the induced current should be much lower with the ABS rings. As any ABS unit works with these signals, there should be a simple solution to this problem. Did you measure the resistance of the ABS sensor? Might give you a hint how to do the amplifying stage and the Schmitt trigger that transforms it into a square signal. Maybe you only need a simple OP-amp stage?
User avatar
By PSIG
#49182
Super Dragpack wrote: Sat Mar 20, 2021 8:14 pmThe VSS is intended to signal the main ECU. No idea why as the AOD is not an electronic transmission. :? Cruise control?
Emissions? :?

So I just hope that the ECU won't mind me piggy-backing off the VSS signal.

Thanks for the help. I may have a play one day with the ABS. Shame I can't use them as 4 spare unused ABS sensors seems a waste. :mrgreen:
Yes, VSS is used for many functions with non-E transmissions, such as the ones you mentioned, plus stuff like traction control (rpm slew rate exceeds set maximum), or transmission/converter trouble codes (engine rpm vs output rpm differential), etc.

The OEM ECM should not mind the piggyback, as the input to Speeduino is high-impedance, and it should not be aware it's there.

As mentioned, the ABS sensors are usable, but you will likely need a different differential amplifier for reliable signal processing to your Arduinos.
#49189
Superb information. Thank you. I knew this was the best place to ask!!!!

You may be correct about the ECU using the VSS for TC diagnostics reasons. The AOD has a lockup TC so it would need to confirm somehow. It may therefore look for a drop in revs-vs-speed to ensure its engaged.

There is also talk of it being used to hold the revs up between shifts etc and better idle control depending on vehicle motion.

Eitherway it works, so I am a happy man. That was the last hurdle before final assembly.

I will show what I have done once it is complete.

Thanks again,

Mick
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