Stabilising Gear position Voltage on C125

[mikepurse]

Hi all and sorry if it’s been asked before but…

I have a gear position sensor going into my pdm input, and can’d to my C125 for gear position. Problem I’m having is my gear display sometimes flicks between gears. Is there away to smooth out the input?

[Stephen Dean]

Hi,

Is this a MoTeC PDM or a different brand of PDM? The Inputs on the MoTeC PDM are not designed for inputs like a Gear Position sensor.

Are you sending the voltage signal from the sensor over CAN, or the calculated position? Is the signal stable in the PDM?

[mikepurse]

Hi Stephen,
It's a Motec PDM30. And its just outputing input voltage on to CAN. Signal in PDM fluctuates very slightly by 0.05-0.1v which is whats causing the issue.

We will be rewiring the car to send the gear position and stick load sensor direct to ECU for better flat shift control but at the moment just wanted the gear display to play ball...

[Stephen Dean]

If you have the C125 to report the gear position based on the voltage that the Gear Position Sensor is putting out for each gear, then you will have this issue if there is some fluctuation in the voltages. The solution to this is to induce some hysteresis into the positions configured in the C125. For example, if the Gear Position Sensor is reading first as 0.5V, second as 1.25V and third as 2V, I would set the voltages for each of these positions in the C125 as 0.75V, 1.5V and 2.25V. By doing this, whenever the voltage is within the specified range (0.0 to 0.75V is first, 0.75V to 1.25V for second, etc.) then that gear will be shown.

This also applies to multi position switches as well.

[SOReilly]

Hi Mike,

Can you upload your Dash config file so we can investigate this further?

[NathanB]

Hi Stephen,
It's a Motec PDM30. And its just outputing input voltage on to CAN. Signal in PDM fluctuates very slightly by 0.05-0.1v which is whats causing the issue.

Hi Mike,

If you refer to to the input specifications in the PDM user manual, you will see that the PDM inputs have an 8 bit AD converter, which paired with the input range of the pin, gives the input pins a 0.2V resolution.

PDM input specifications.jpg (70.52 KiB) Viewed 13768 times

This lines up with your voltage fluctuation. Anything you attempt as a fix is just going to be a bandaid solution. The only way to correctly rectify the situation is to wire the gear position sensor to a suitable input (not of the PDM).

[mikepurse]

Thanks for the replys guys. I think Nathan has nailed it, so will rewire direct to Life Ecu and send it to dash.