MoTeC Global Forum

Hi guys, I got my I/O upgrade code and Temperature sensor connected. I got the sensor from an innovate Motorsports gauge I am not using.

I reached out to them for a calibration and this is what they returned to me:
The reistance values seem too low to me and they cannot be entered in the format into the calibration. 0.3000 will become 0 I am unsure what the other columns to the right are. (3000.0000, 2.631579 etc.)
Someone mentioned that maybe I was provided voltages?

So I am wondering I should set the Calibration Method to "Absolute Voltage or Ratiometric (5v))"

If someone can please help me figure this out it would great. I have unlocked for I/Os and Custom displays and I would love to use it on the track this coming weekend.

I also have an LC2 wideband controller whose output 0-5V I want to read, plus a 0-5V pressure sender.
Should those be configured at Absolute voltage or ratiometric?

If you are supplying the sensor with 5V (if required, AT's have an internal pullup to the 5V rail) and using the Displays 0V pin, then set it as a Ratiometric device, If it has an external supply, then use Absolute.

With the Calibration table, multiply the Ohm values by 1000 and enter them, then test the sensors result against a know good sensor/thermometer at a couple of different points, and see how that compares. Otherwise you can use one of the internal calibrations and see if one of them matches the sensors output.

My wideband has its own 5v and ground (ground shared with tc125) so that should be set to Absolute.

My oil pressure sender, 3 wires, get 5v from the c125 and are grounded as per above.

I just noticed some discrepancies on the wiring schematic from the C125 race loom (which I own) and the C125 I/O Loom which I replicated.

See similarities in yellow
differences in orange
Green - is the only place I see 0V.

Please let me know is there is an error in these document before I tear up my harness again - which gets pretty expensive quickly. The GPS is and has always been working referenced to chassis battery ground.

This leads to another question. My LC2 is also grounded to the battery and so is the C125. Is this going to be a problem trying to read the 5V signed from the LC2?

I understand there is a difference between ground and 0v but please help me make this right.

Thank you

I also wanted to add the the cut sheet for the GPS-L10 references Battery Ground.
So far, it seems that C125 Race loom is correct and its working physically in the car..

somehow the sensor seems to be working. I think that maybe my plug (electrical connection to the sensor was not making full contact).

It was helpful to mulitply all the values by 1000.

My connections for ground for the sensors IS to Battery ground. I am wondering if the PDF document for the C125 accessory loom needs to be updated. If I need to reference the 0v pin on the dash, please let me know

Just because the sensor is working now doesn't mean it is correct.
I wait a response before I dig into my harness.

Thank you.

Theoretically you should always wire sensors to the 0V rather than the chassis ground. This is simply because the A/D converters are referenced to the 0V and the 0V has its own protection/filtering circuitry.

In reality the 0V and chassis ground are internally connected in the dash and because you are running wiring all the way back to the dash rather than using the chassis itself it is unlikely you will see any difference in the sensor readings. The only time you would have issues is if you are using the chassis of the car as the ground for a sensor.

I have however asked for an engineering change to be made to the C125 Race Loom to change the wiring to the GPS from a ground to a 0V so that it is technically correct. If I was you I wouldn't bother modifying the wiring as you will not see any difference in sensor readings.

^
thank you for you help. Your response makes sense and I was wondering how the 0V would be any different for me.
Yes I am running the Neg wires from my sensors up to neg Battery pin on the back of the C125. An as previously instructed on a separate thread (by you I think) my dash grounded directly to the battery via a relay; it is on it own circuit only shared by my wideband controller.

On your last sentence. You are saying the GPS will be grounded on the 0V pin in future? Or are you adding a 0V wire to the vacant GPS connector?
I have already opened the harness. Maybe I will just switch it to the 0V.

The GPS will be grounded via the 0V pin. That way the I/O loom can remain unchanged.

Can I / would it be safe to make the change on my loom? (for the gps to use the 0v)