auxilliary input: can its range be increased?

[studarude]

Hi all,

the other niggle ive got left is to sort out the input from my temp sensor for map correction, im using the standard 205 GTI temp sender which when plugged in gives a max reading on the Megajolt of the 255 i think when cold, is there any way of increasing the range (or at least 'offset' the range) so that i can use the standard sensor?

My limited calcs with regards to thread sizes tell me that the GM sender at 3/8NPT is just over 16mm, so i could junk my M14 sender and re-tap, if i can, id like to avoid this.

[NITROPIXIE]

Instead of using the thermistor input, you could use the variable voltage input instead with a voltage divider.
http://www.autosportlabs.net/MJLJ_V4_ve ... put_source

Basically find the resistances of the thermistor at cold temperature and running temperature. Normally with heat the resistance drops.

Obtain a resistor, a value near the max. resistance of the thermistor.

Create a simple voltage divider circuit with the resistor connected from VREF to AUX INPUT of MJLJ and the thermistor connected from AUX INPUT to GND of MJLJ. This will give you circuit of range 0v to 2.5v at the very extremes of temperature. If this doesn't give you enough voltage range then you can reduce the value resistor.
http://www.autosportlabs.net/MJLJ_V4_ve ... guidelines

You will need to also make the board modification to do this. http://www.autosportlabs.net/MJLJ_V4_ve ... dification

[brentp]

Hi studarude,

Do your readings on the aux input change at all when the engine warms up? If you get a reasonable change in values from cold to hot then you can just re-calibrate the sensor using the software. See:

http://www.autosportlabs.net/MJLJ_V4_Op ... figuration

You'll see that by default, the raw "ADC value" is mapped 1 for 1 to the displayed value. However, you can change this mapping to match the particular curve for the sensor you're working with- even invert the curve if necessary.

If, for some reason, you need to change the voltage divider resistor you can change the value of R6 to something else- just wanted to point out that the voltage divider circuit is already built into the board by default.

Regards,

[NITROPIXIE]

That would be an easier solution,lol

[studarude]

Hi all,

I managed to get this sorted now, and still managed to keep my existing temperature sender. Like you guys said, it was simply a matter of inverting the scale on the table, but to get there i first needed to get a set of values, so i removed the sender (whilst still connected and Megajolt software running) and placed it in a kettle with a digital thermometer.

Switched the kettle on, and then took readings every 5degrees as it heated up in relation to what the software reading was. I then plotted a curve in excel with a best fit line, and voila, all the data range, even for something as nonlinear as the thermistor.

Ive saved the calibration file, so ill happily upload this should it help someone.

[NITROPIXIE]

Good to hear you have it all sorted now.