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Thermistor stuck at 275°C

Posted by Atfer 
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Atfer
Thermistor stuck at 275°C
November 19, 2011 04:11PM
Hello again! I just got this strange problem that appeared suddenly : My thermistor temperature is at 275°C and won't change. If I connect my thermistor to my heated bed input, it shows the good temperature. I tested with my voltmeter the two pin of the extruder thermistor on my ramps1.4, and I can see that current goes trough these, I don't that with the other thermistor input. Is that software related or is something broken? Thank you!


BTW, sorry for flooding the forum, but my project is almost done!
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brupje
Re: Thermistor stuck at 275°C
November 20, 2011 04:30AM
Maybe your thermistor is shorting soemwhere?


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Atfer
Re: Thermistor stuck at 275°C
November 20, 2011 11:33AM
No, because when I plug it in the bed input, it is working, so the resistor is not the problem, it come from the board.
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Atfer
Re: Thermistor stuck at 275°C
November 20, 2011 03:29PM
Ok, I found that the problem come from the arduino itself. I tried to export the firmware again, but it didn't change a thing. I don't understand how is that possible. It was working like a charm and then not. Is there a way to test if everything is alright with it?

One solution I could see is to use the second extruder thermistor input, but I didn't find what to change on the firmware to change this. If someone could help me!

I use a Ramps1.4 with a Arduino mega 1280.

thanks


PS: When the Ramps is disconnected from the arduino, I see the temperature T:357 B:179 (or 184). When I plug the ramps back in, I see T:278 B:0.

Edited 1 time(s). Last edit at 11/20/2011 03:32PM by Atfer.
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nophead
Re: Thermistor stuck at 275°C
November 20, 2011 04:25PM
Quote

I don't understand how is that possible. It was working like a charm and then not.

This is usually caused by a short between the thermistor and the heater. It puts 12V on the Arduino pin which destroys the input circuit.

[www.hydraraptor.blogspot.com]
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Atfer
Re: Thermistor stuck at 275°C
November 20, 2011 04:40PM
nophead Wrote:
-------------------------------------------------------
> I don't understand how is that possible. It was
> working like a charm and then not.
>
> This is usually caused by a short between the
> thermistor and the heater. It puts 12V on the
> Arduino pin which destroys the input circuit.

I see how that could be a problem... So is there a way to change the input, since that one is destroyed?
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ECSuyu
Re: Thermistor stuck at 275°C
November 20, 2011 06:58PM
the only way is to cut the pin going to your pin0 from your ramps and reroute it to one of the pins thats not being used.

A good and easy to test and make sure its the arudino is to check the resistance with a multimeter when the arudino is powered on. the input pins should have a resistance reading if its working if not it'll read 0
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Atfer
Re: Thermistor stuck at 275°C
November 20, 2011 08:11PM
Thanks for your answer, I've looked for the resistance : The working pin shows a resistance of 696 ohm, the broken one shows 152 ohm. It is lower, but it's not 0. I don't know if it is possible to compensate with the firmware? If not I guess I'll have to order and wait for a new arduino.
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ECSuyu
Re: Thermistor stuck at 275°C
November 20, 2011 08:34PM
I dont know about compensating for it in the firmware as I actually had the same issue as you at one point. It happened to be my pin0 was showing no resistance upon replacing the arduino it was fixed. But make sure nothing is shorting out, because if thats the case it'll just happen again.
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Atfer
Re: Thermistor stuck at 275°C
November 20, 2011 11:00PM
I've been looking over the forum about how to use the second extruder with the RAMPS1.4, but I don't find any documentation. If it is possible, I could just switch everything in the second extruder. But if it is too complicated and could result in issue, I'll just buy a new arduino. Thanks for your help!
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brnrd
Re: Thermistor stuck at 275°C
November 21, 2011 12:48AM
What firmware are you using? If it's Sprinter or Marlin, you can just edit your pins.h file. Look for TEMP_0_PIN (usually for extruder 1) and swap the assigned number with TEMP_2_PIN (usually for extruder 2) as follows:

#define TEMP_0_PIN         13   // ANALOG NUMBERING
#define TEMP_1_PIN         14   // ANALOG NUMBERING
#define TEMP_2_PIN         15   // ANALOG NUMBERING

to

#define TEMP_0_PIN         15   // ANALOG NUMBERING
#define TEMP_1_PIN         14   // ANALOG NUMBERING
#define TEMP_2_PIN         13   // ANALOG NUMBERING

Edited 1 time(s). Last edit at 11/21/2011 01:01AM by brnrd.
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Atfer
Re: Thermistor stuck at 275°C
November 21, 2011 08:51AM
This is what it was looking for! Thank you! I'll try it and try not to kill the other pins this time.

EDIT : It worked! I've been looking for the pin assignment in the firmware but couldn't find it. I looked in the thermistor table, but didn't notices the pins tab (working on a Eeepc is harder than expected).

Edited 1 time(s). Last edit at 11/21/2011 08:58AM by Atfer.
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alex_rycroft
Re: Thermistor stuck at 275°C
January 05, 2012 07:53PM
Hi there,

I am a newbie with the same problem.

I went to the trouble of extending cables to run into an enclosure to tidy up my Mendel. In the process I have fried the T0 thermistor pin.

Everything else works fine and I am getting all the same symptoms as Atfer.

So I need to reroute as suggested by brnrd.

How do I do this?!

I am running a preconfigured Arduino Mega 2560 R2 with RAMPS V1.4. I would just like to view and edit the current Sprinter firmware (V1.0) not load new firmware as I would have to reconfigure all the stepper variables etc.

I have the Adruino software installed and get the "start" response from the board when I connect to the serial monitor. Where do I go from here?

Thanks!

Alex.
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Andrew Smith
Re: Thermistor stuck at 275°C
January 05, 2012 08:14PM
Can't be done, you need to upload a fresh firmware. With luck, whoever sold you the preconfigured board can provide the config.h they used, otherwise you're going to have to set it up from scratch.
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alex_rycroft
Re: Thermistor stuck at 275°C
January 05, 2012 08:24PM
Thanks Andrew,

I'll give that a go.

Cheers,

Alex.
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alex_rycroft
Re: Thermistor stuck at 275°C
January 05, 2012 11:42PM
Ok,

So I have successfully uploaded the tweeked Sprinter firmware onto my board using Arduino 0023 and am getting correct thermistor readings from the T1 input.

However, Repsnapper no longer shows the value in the temperature box and therefore will not turn the element on. When looking at the reply from the board it comes back with both the extruder and bed temp (T0 and B0) and a lot of asterisk's where it used to only come back with the extruder temp.

Any ideas on how to fix this?

I have tried using the reprap software but it always crashes. Maybe because I am using 64bit...

Would be great if Repsnapper could work again as I was just getting the hang of it + Skienforge together.

Thanks!

Alex.
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brnrd
Re: Thermistor stuck at 275°C
January 05, 2012 11:51PM
Use the precompiled pronterface instead of repsnapper.

pronterface is [github.com] and precompiled for windows (without sfact) at [koti.kapsi.fi] & precompiled for OSX (without sfact) at [koti.kapsi.fi]
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alex_rycroft
Re: Thermistor stuck at 275°C
January 06, 2012 01:45AM
Thanks brnrd,

Got it all back up and running again, however after lengthening the endstop cables and running them alongside the stepper cables I think I may be inducing some noise and triggering a false end position.

This is what is happening. Jog in the +ive direction, no worries at all. Press home in any of the 3 axis and the head or bed will move a random amount then slow and stop. Press home again and again until it finds actual home. Similar with jogging in the -ve direction, it moves the desired amount most times but just moves a little other times like it thinks it has hit home.

Any ideas?

Maybe I should start a new thread for this?

Thanks,

Alex.

EDIT - This was happening before I updated the firmware but only after I lengthened cables so I may have created a short somewhere...

Edited 1 time(s). Last edit at 01/06/2012 02:55AM by alex_rycroft.
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nophead
Re: Thermistor stuck at 275°C
January 06, 2012 04:28AM
If you run the endstop cables along side the motor cables you get inductive coupling that gives false triggers.

I fix that with a retry loop in my homing code but you could also run the wires separately or use RC filters on the endstop inputs.

[www.hydraraptor.blogspot.com]
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brnrd
Re: Thermistor stuck at 275°C
January 07, 2012 09:21AM
In addition to running the wires far from the motor wires, I wonder if it would also be better to use shielded twisted pair or small coaxial cable for the thermistor connection and to fix this. In my Mendel, I made sure to twist the motor wires together to reduce noise and I used ribbon cables for the thermistor. Since the ribbon cable wires are very close to each other, it provides some noise cancellation. I haven't seen any issues with my endstops.
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nophead
Re: Thermistor stuck at 275°C
January 07, 2012 10:20AM
I have only had the problem with twisted pairs running next to each other for some distance, or ribbon cables.

With twisted pairs, spacing them a few mm apart is sufficient. In the last picture here: [hydraraptor.blogspot.com] you can see I made some dual cable clips for the Y and the Z wires and they work fine. The X axis uses a ribbon cable and that has crosstalk. The only other time I have had cross talk is when I ran some twisted wires next to each other in a bundle from the motor to the controller.

Screening may work, I not sure though as I think the coupling is magnetic rather than electrostatic / capacitive.

[www.hydraraptor.blogspot.com]
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alex_rycroft
Re: Thermistor stuck at 275°C
January 08, 2012 11:01PM
I have now run the opto cables separately and all seems fine.

Thanks for your help!

Alex.
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ijmok
Re: Thermistor stuck at 275°C
January 09, 2012 06:03AM
Hi,

Not 100% Relevant to you per say but it happened to me other the weekend and is linked so thought id post it
My Ramps was playing up badly – T0 showing up between 130 - 500 deg with nothing connected
The thermostor read correctly on the bed input so that side seemed ok
Probing about it seems my ramps board had got a bad joint on the thermistor pin into the arduno (analogue pin 8?)
Resoldered it back up and its working fine
Thought id add it for others incase they run into it
Rob
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