problem reading thermistor values with RADDS+ArduinoDue

Hello guys,
I need your help with the thermistor configuration!

In the last two years I've built a mendelmax1.5 and now I have designed my own 3printer with ArduinoDue and RADDS.
I've always checked this forum because of the huge amount of information I can find, and that always helped a lot to solve my problems.
But now I'm stuck! :-(

So, what's the problem?

- I upload Repetier firmware (0.92.8) with the correct configuration: RADDS + ArduinoDue + thermistor 0 as a ATC Semitec 104GT-2 (coming from an original E3DV6)
- I open RepetierHost and connect to my ArduinoDue+RADDS board without any problem
- in the manual control tab I can move all the axys without any problem
- in the same tab I can see a wrong temperature (-20) and obviously I receive the error "temp sensor defect marked defect"


In the past few days I've tried a lot of methods to solve this issue:

- I'm pretty sure it's not an HW problem (everything checked with a digital multimeter on the boards: 4,7K pull-up resistors, capacitors, scheme)
- If I open the IDE serial monitor and check the values of thermistors (now I don't remember the code I used) the value change from 0 to 1023 (short on the T0 pins or open pins)
- the voltage on the T0 pins, with the thermistor connected, is 3,2V @ 22°Celsius (and it decreases if the temperature goes up)
- what is very strange if I heat up the thermistor, manually, whit a heat gun, when it reaches an high temperature I can see the temperature on the RepetierHost starting to increase (not correct values, althought)
- I tried a lot of thermistor tables, manual thermistor tables with some interesting result:
I managed to obtain a starting temperature of 0° or even 20°C with no message error; but when I switch on the extruder, nothing move till the real temperature is, let's say for instance 130°C (I have a digital thermometer)
- it looks like the firmware is not calculating correctly the values (the formula, the Voltage reference, or WTF)
- but at the same time I've tried other firmwares with no result (even older Repetier versions)
-already checked with other 100k spare thermistors

I'm lost, I don't understand what's going on and I need your help!


P.S. Thanks for this wonderful piece of software (and firmware) Repetier! :-)

Edited 1 time(s). Last edit at 01/24/2016 10:06AM by mignolo4.

Looks like a hard one. Also no idea what goes wrong. Things to try

1. use M105 X0 so you get raw values as well. These should change with temperature
2. Try T1 instead in case there is something wrong with the pin it self on the due.

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First of all, thank you very much for your reply!

I've been busy in the last few days, but in the evening I tried to get to the bottom of it.

- I connected a 22KΩ potentiometer on the T1 Pin (thermistor ATC Semitec 104GT2 in the firmware)

To let you understand what I discovered, these are the most significant results with the M105 X0 code:

T: -3° RAW0 4044 (with 6,5KΩ and 1,89V)
T: 85° RAW0 2680 (with 2,6KΩ and 1,23V)
T: 969° RAW0 3 (with 20Ω and 20mV)

So I obtain the (almost) highest RAW value with only 1,9V and that's very strange...

1,89V sound not so wrong. Remember the pin we read is between 4.7K and your 6.5K so just not in the center of 2.5V.

So maybe the thermistor is just a different type. Have you measured resistance at room temperature? Should be near 100K at 25°C.

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Repetier-Software - the home of Repetier-Host (Windows, Linux and Mac OS X) and Repetier-Firmware.
Repetier-Server - the solution to control your printer from everywhere.
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Solved!!!

Following this discussion [forums.reprap.org] (third page) I realised that that was my exact same problem

To summarise:
I have got a faulty Arduino Due Clone (reprap.me) with a wrong JR1 resistor (it should be 0 Ω )
Since the JR1 resistor affects the reference 3.3V, soldering some tin on top of that resistor (thus making a short) solve the problem! Urray :-)

Edited 3 time(s). Last edit at 02/08/2016 06:18PM by mignolo4.