Thermistor inputs aren't working

[Generic Default]

Hi everyone,

For a few weeks now my bed temperature has been reading about 109 degrees C even though it's at room temperature. I thought the thermistor must have broken somehow until just tonight when I tried plugging in another thermistor for a second E3D hotend. hotend2 temperature read 105 degrees at room temperature when plugged into thermistor2.

I switched the wiring so that hotend2 was plugged into the thermistor1, and it read 21.5 degrees (correct). When I did that, the temperature for hotend1 (plugged into thermistor2) showed 105 degrees. I did the same thing for bed thermistor and found that all three thermistors are working, but they only read correctly when plugged into thermistor1.


Then I heated up hotend2 while it was plugged into thermistor2 and saw that the temperature was increasing from 105 degrees to around 115 degrees (the actual temperature was probably around 220 degrees).

The same thing happens with my heated bed. So all of my thermistors are working correctly, but they only show the correct temperature when plugged into the thermistor input meant for hotend1. They are still receiving some sort of signal from the other two thermistor ports, but it isn't accurate.
Here are some relevant firmware settings;

Code: Select all

// What type of sensor is used?
// 1 is 100k thermistor (Epcos B57560G0107F000 - RepRap-Fab.org and many other)
// 2 is 200k thermistor
// 3 is mendel-parts thermistor (EPCOS G550)
// 4 is 10k thermistor
// 8 is ATC Semitec 104GT-2
// 5 is userdefined thermistor table 0
// 6 is userdefined thermistor table 1
// 7 is userdefined thermistor table 2
// 50 is userdefined thermistor table 0 for PTC thermistors
// 51 is userdefined thermistor table 0 for PTC thermistors
// 52 is userdefined thermistor table 0 for PTC thermistors
// 60 is AD8494, AD8495, AD8496 or AD8497 (5mV/degC and 1/4 the price of AD595 but only MSOT_08 package)
// 97 Generic thermistor table 1
// 98 Generic thermistor table 2
// 99 Generic thermistor table 3
// 100 is AD595
// 101 is MAX6675
// 102 is MAX31855


#define EXT0_TEMPSENSOR_TYPE 1
// Analog input pin for reading temperatures or pin enabling SS for MAX6675
#define EXT0_TEMPSENSOR_PIN TEMP_0_PIN

#define EXT1_TEMPSENSOR_TYPE 1
// Analog input pin for reading temperatures or pin enabling SS for MAX6675
#define EXT1_TEMPSENSOR_PIN TEMP_2_PIN

#define HEATED_BED_SENSOR_TYPE 1
/** Analog pin of analog sensor to read temperature of heated bed.  */
#define HEATED_BED_SENSOR_PIN TEMP_BED_PIN

Does anyone know how to fix this?
Thanks!

[mhackney]

Did you make any firmware changes several weeks ago? This really sounds like a pin configuration issue. What controller board are you using (RAMBo, RAMPS, etc?) and which firmware (looks like Repetier)? Look at the pin assignments for the temp ins in pins.h and depending on which board you are using, we can verify that.

cheers,
Michael

[Lochemage]

Sounds very much to me like your firmware is configured for the wrong thermister types. Every type of thermister has their own table of resistance to temperature values, a wrong table assigned to a thermister will end up showing the wrong temperature values. Are your thermisters both the same exact type, or are they different? Perhaps some closeup pictures of the actual thermisters might help identify which thermister types you are using (also if you have receipts for where you bought them, they could also identify them as well).

It would explain a lot if either both of your thermisters were different and/or your firmware has assigned two different tables for your bed and hotend. In this case, changing which one plugs into which would drastically change the temperature reading you see on both.

[Generic Default]

The bed thermistor is the one type that came with the SeeMeCNC onyx heated bed, which I think is the Epcos B57560G0107F000. The other two thermistors came with E3D hotends, and the website says they're also Epcos B57560G0107F000.

I don't think I made any firmware changes at the time this problem started, and if I did, it would only be minor changes to the delta radius setting.

Right now I'm running the newest Repetier 0.91 firmware on the Rambo board. The settings in my first post show that each input is working with the Epcos B57560G0107F000 thermistor table, but the 2nd and 3rd inputs are showing weird values.

[Lochemage]

I suppose it might depend on how recently you bought them... The ones that came with my rmax kit (as of about 3 months ago) were type 8: ATC Semitec 104GT-2, and the ones I got from my E3D kit were also the same.

As far as I've seen, type 1's were common a while ago but now type 8's are what I see everywhere.

[Polygonhell]

you'll see almost no difference in temperature reading at room temperature between type 8 and type 1

If it doesn't work as type 1 the odds are either the pin is configured incorrectly, the wiring is bad (easily established by swapping to the working connection) or you've damaged the thermistor pin.

Unfortunately the way the analog pins on an arduino are exposed and wired on the Rambo (and pretty much every other controller) they are extremely delicate and any over voltage, i.e. shorting to power pins is pretty much guaranteed to damage them.

[Generic Default]

I found this in the pins.h file in the rambo section;

Code: Select all

#define HEATER_BED_PIN 3
#define TEMP_BED_PIN   2

#define HEATER_0_PIN   9
#define TEMP_0_PIN     0

#define HEATER_1_PIN   3
#define TEMP_1_PIN     2

#define HEATER_2_PIN   7
#define TEMP_2_PIN     1

Can someone please check to make sure that's the normal configuration? It doesn't make sense to me that the bed pin and the temp1 pin are the same, but I don't want to change it and mess stuff up if it's supposed to be like that.

Also, I really doubt I damaged the pins because I haven't messed around with the wiring for a while. The board looks fine after a visual inspection; nothing fried.

[mhackney]

That is correct. There are 2 types of pins - digital and analog - and they both start numbering at 1. Confusing.

[mhackney]

After thinking about this a bit, I suspect you have blown the thermistor circuits on these two inputs. It is *very* easy to do. If you did any wiring or accidentally shorted the thermistor leads, you probably toasted them. The Rambo has 4 thermistor inputs, did you try the 4th one?

[Generic Default]

Woah, serious problem. I have NUM-EXTRUDERS set to 1 in both the firmware and in repetier host. In repetier host I started heating up the hotend but stopped when I noticed that both of the E3D hotends were getting hot. I turned off the "Heat Extruder" button in repetier host so I could look through the firmware code. A few minutes later I smelled smoke and saw that my hotends were about to catch on fire, so I turned off the power supply.

Here are some relevant settings in my firmware right now;

pins.h

Code: Select all

#define HEATER_BED_PIN 3
#define TEMP_BED_PIN   2

#define HEATER_0_PIN   9
#define TEMP_0_PIN     0

#define HEATER_1_PIN   3
#define TEMP_1_PIN     2

#define HEATER_2_PIN   7
#define TEMP_2_PIN     1

configuration.h

Code: Select all

#define EXT0_TEMPSENSOR_TYPE 1
// Analog input pin for reading temperatures or pin enabling SS for MAX6675
#define EXT0_TEMPSENSOR_PIN TEMP_0_PIN
// Which pin enables the heater
#define EXT0_HEATER_PIN HEATER_0_PIN

#define EXT1_TEMPSENSOR_TYPE 1
// Analog input pin for reading temperatures or pin enabling SS for MAX6675
#define EXT1_TEMPSENSOR_PIN TEMP_1_PIN
// Which pin enables the heater
#define EXT1_HEATER_PIN HEATER_2_PIN

I really hope my thermistor circuits aren't fried. I just doesn't make sense that the first input works fine and the second two don't read accurate temperatures. I have only used the first and the third inputs until now (for the heated bed and the hotend); the second and the fourth inputs have been unused until this point. How would I check to see if the fourth input works?

[Generic Default]

Another note;

When I turn on my rostock, only the green LED is working on the rambo. When I turn on "Heat Extruder" in repetier host, two red LEDs turn on near it. When I turn off "Heat Extruder", one of the LEDs turns off but the other one stays on. The only way to turn it off is to turn off the power supply. The LED that stays on indicates that the second hotend is getting power, so it continues to heat up. The first hotend stops heating with the first LED.

[Polygonhell]

If you're using the same configuration as the SeeMe CNC firmware you need to disable the extruder fan, which is set as the extruder 2 output by default, if you don't it will be on full power anytime the first Hotend is over 50C.

[Generic Default]

I just tried a bunch of pin changes in the firmware over the last hour, and I think I might be able to get this to work. Thermistor inputs 0 and 3 are working with accurate temperature readings for both hotends. Since there are four thermistor inputs (0-3) and I need to check 3 temperatures, I think the best solution for now is to simply use inputs 1 and 3 for both hotends, and keep the bed thermistor wired to thermistor input 1 or 2. The bed temperature isn't critical for printing with nylon, so I'll have to not use it for now. Hopefully I can fix it in the future, though. Since it's plugged into a defective thermistor input, it reads 119 degrees at all times.

THERMISTOR INPUT 0 ------ Works fine
THERMISTOR INPUT 1 ------ Reads 120
THERMISTOR INPUT 2 ------ Reads 109
THERMISTOR INPUT 3 ------ Works fine


There is a small fuse next to the thermistor pins on the rambo board. Does the fuse have anything to do with this? How can I fix pins 1 and 2 for future use?

And thanks to everyone who has been helping me with this so far!

[mhackney]

The fuse next to the thermistor inputs is for either the extruders/fans or motors/logic (I can't recall which), the small devices on the other side are capacitors, not fuses.

Back in the old days we controlled out heated beds with an external thermostat. It was a kit made by Vellman. I have 2 new-in-the-box kits laying around if you want one of them, just pay the postage and I'll ship it. $5 USPS priority anywhere in the US and you would likely get it by the weekend.

Also, Ultimachine will repair/replace blown boards for a small fee. Don't ask me how I know!

cheers,
Michael