Car transmission TCC-control, noise in VSS-signal

Hi,

I made a potentiometer adjustable Arduino solution to
control my truck's ('86 C10 w/TH700) Transmission Torque Converter Clutch apply speed.

The Vechicle Speed Sensor wire going to Cruise Control module is giving square wave
(approx 1Hz/ km/h) and is connected to Arduino digital input. The pin has 3k pull up resistor.
Tried pull down too, it does not work.

The system works as planned in principle and i have a temporary LCD on it to see what is happening.

The problem is; when Arduino is connected to the VSS wire, the VSS signal gets erratic
once in a few minutes time frame and jumps up. I can see on LCD that vechicle speed is
for a split second suddenly from, say, steady 80km/h to 200-300km/h,
and when this happens the cruise control of course commands the servo to pull off,
making Cruise Controlled ride inconvinient.
When Arduino is not connected the Cruise works as it should.

What could cause this disturbance signal in VSS with Arduino and how to filter it out?

thanks.

pocale:
Hi,

I made a potentiometer adjustable Arduino solution to
control my truck's ('86 C10 w/TH700) Transmission Torque Converter Clutch apply speed.

The Vechicle Speed Sensor wire going to Cruise Control module is giving square wave
(approx 1Hz/ km/h) and is connected to Arduino digital input. The pin has 3k pull up resistor.
Tried pull down too, it does not work.

The system works as planned in principle and i have a temporary LCD on it to see what is happening.

The problem is; when Arduino is connected to the VSS wire, the VSS signal gets erratic
once in a few minutes time frame and jumps up. I can see on LCD that vechicle speed is
for a split second suddenly from, say, steady 80km/h to 200-300km/h,
and when this happens the cruise control of course commands the servo to pull off,
making Cruise Controlled ride inconvinient.
When Arduino is not connected the Cruise works as it should.

What could cause this disturbance signal in VSS with Arduino and how to filter it out?

thanks.

Q1) What is the Min / Max voltage on the VSS wire when not connected to the Arduino?

Q2) Why do you think you need to apply a Pull-Up Resistor or Pull-Down Resistor on the VSS Wire?

Q3) What does this mean, "I made a potentiometer adjustable Arduino solution to
control my truck's ('86 C10 w/TH700) Transmission Torque Converter Clutch apply speed." in simpler terms?

Hi, thanks for the response.

Q1) What is the Min / Max voltage on the VSS wire when not connected to the Arduino?

Actually i dont know. My multimeter is not very good to follow up with voltage pulses. AFAIK there is an amplifier between the Cruise module and speed sensor. The fact that it works with a pull up resistor says to me the square wave is to ground.

Q2) Why do you think you need to apply a Pull-Up Resistor or Pull-Down Resistor on the VSS Wire?

It's been a while i played with Arduino last time. But i remember read somewhere it is good to have a pull up/down resistor to prevent the pin floating around the trigger. Is that right? I might need to give it a try without the pull up. Can the pull-up be creating weirdos in the signal?

Q3) What does this mean, in simpler terms?

The truck is Chevrolet Pick up. Automatic transmission with Torque Converter Lock up feature. The Lockup is hydraulically controlled inside transmission to may apply only on 3rd and 4th gear and electronically controlled on based Vechicle speed and Throttle position. However, the truck has changed gearing, torque converter etc, so the original TCC control don't work as i like. applying way too soon (below 60km/h). That's why i have this Arduino to read Vechicle speed and adjustable potentiometer set then relay the original control wire closed.

HowStuffWorks about TCC: "In addition to the very important job of allowing your car come to a complete stop without stalling the engine, the torque converter actually gives your car more torque when you accelerate out of a stop. Modern torque converters can multiply the torque of the engine by two to three times. This effect only happens when the engine is turning much faster than the transmission.
At higher speeds, the transmission catches up to the engine, eventually moving at almost the same speed. Ideally, though, the transmission would move at exactly the same speed as the engine, because this difference in speed wastes power. This is part of the reason why cars with automatic transmissions get worse gas mileage than cars with manual transmissions.
To counter this effect, some cars have a torque converter with a lockup clutch. When the two halves of the torque converter get up to speed, this clutch locks them together, eliminating the slippage and improving efficiency."

Try using the "Smoothing/Averaging" method. I was getting what I think is EMI causing erroneous signals to be injected into the VSS input to Arduino thus causing erratic readings. I averaged a certain number of readings and it cleared up.

Bill