Measuring temperature with i.MX286 via PT1000

[christiank]

Hi!
I want to measuer the temperature with the chip mentioned above.
In the refence manual is only stated, that the sensor can be connected. My question ist: how? I tried to connect ot between ADC0 and GND with inducing a current of 100µA and 300µA, but the results is nrearly constant at 2215 digits (with 1/2 divider).
There is no other source connected. My fluke tells me there is only 50mV between these two pins...
Futhermore I have not found the corredponding maximum voltage to 4095 digits without divider.

I hope you can help me.
Best regards
Christian

[igorpadykov]

Hi Christian

for ADC voltage measuring (please check i.MX28 EVK spf-26241 schematic
p.15 on links below) one can look at OBDS example keypad/../stmp-keypad.c

Schematics (3)
i.MX28 EVK Design Files: Hardware Schematics, Gerbers, and OrCAD files (REV 1.01)

Lab and Test Software (1)
On-Board Diagnostic Suit for the i.MX28 (REV 1)
http://www.nxp.com/products/software-and-tools/software-development-tools/i.mx-software-and-tools/i....

Best regards
igor
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[christiank]

Hallo igor,

thank you for your answer. The linked files are very useful for further development.

I have no trouble with ADC in general. I am referring to chapter 38.2 of the i.MX28 reference manual where is stated:

The LRADC channels 0 and 6 have optional current source outputs to allow these channels to be used with an external themistor (or an external diode) for temperature sensing. The controls for these current sources are in HW_LRADC_CTRL2.

I would like to know how to use this feature properly.

Thank in advance

Christian

Edit Addition:
Now I have tried to measuer with ADC1 the voltage over the PT1000 while ADC0 should drive the current. But I always measuer about 50mV, independent of the given current. This value does not change. This value corrensponds to the reading with a multimeter.