Dear gr5,
thanks for your reply ,I've measured the voltage of feedback and it reports 1.16v for room temperature , and 1.6-1.8v when I place the thermocouple in my mouth !
this is the thermocouple I'm using ::http://www.aliexpress.com/snapshot/6106857710.html
and this is the IC for small circuit board ::http://www.aliexpress.com/store/product/Free-Shipping-5PCS-AD597ARZ-AD597-SOP-8-IC/614856_1722843997.html
whats your opinion ?
The link to aliexpress does not show a thermocoupler. It shows a 100K thermistor. In that case you don't need the extra amplifier on the printerhead. You can connect it to the UM electronics directly and add a 4k7 resistor to the +5V. Then you need to flash the correct marlin software that is configured for a 100K themistor for the hotend.
Or is your board different from the UM original board....
Dear Zoev89,
I've done what you said ,and now everything is working BUT it shows 11c for room temperature!
do you have any solution for this problem?
my first guess was that the thermistor is not properly attached to the aluminum cube on print head and there is air between the aluminum and thermistor !
or is there another problem ?!
Hi Amirps.
For room temperature it would not matter how it is connected to the heater block. Does the sensor react to higher temperatures in a linear way? Heat it up to know temperatures. If it does that then it looks to me that the characteristic is different then Marlin expects. In know Marlin has a couple different 100K thermistors and it might be the solution is in that area. There are possibilities to calibrate the characteristics but I have no experience in that field. Measuring 11 degrees for room temperature is cold unless it is really cold in the room...
Most Thermistors are not rated above 250F (let alone 250C!) They will get permanently damaged at those temperatures such that they read the wrong temperature. Each time they go above 150C or so they get damaged further and the temperature/resistance gets more and more inaccurate. Because of this we usually only use thermocouples thermistors for the heated bed (which shouldn't get above 110C).
You can probably order a thermocouple from Ultimaker. You would need to get one with the exact same characterstics that the UM Original print head circuit board expects
edited by gr5 (see X out above).
I guess you mean to say:
Because of this we usually use thermistors for the heated bed.
Hi Amirps.
For room temperature it would not matter how it is connected to the heater block. Does the sensor react to higher temperatures in a linear way? Heat it up to know temperatures. If it does that then it looks to me that the characteristic is different then Marlin expects. In know Marlin has a couple different 100K thermistors and it might be the solution is in that area. There are possibilities to calibrate the characteristics but I have no experience in that field. Measuring 11 degrees for room temperature is cold unless it is really cold in the room...
Dear Zoev89,
I changed my configuration ,and yes, it's working fine ! now the room temperature is 26c 
but problems raise one after another :-|
I want to print a model everything is working fine the head is moving in the right path ,but the feeder motor is not working ,I've tested the wires and the driver IC they have no problem .
Most Thermistors are not rated above 250F (let alone 250C!) They will get permanently damaged at those temperatures such that they read the wrong temperature. Each time they go above 150C or so they get damaged further and the temperature/resistance gets more and more inaccurate. Because of this we usually only use thermocouples for the heated bed (which shouldn't get above 110C).
You can probably order a thermocouple from Ultimaker. You would need to get one with the exact same characterstics that the UM Original print head circuit board expects.
Dear gr5,
you mean that thermistor is not good for using in Ultimaker original ? and how is that you said "use thermocouples for the heated bed (which shouldn't get above 110C)" ? the default temperature is 220c in Cura:-\
would you please explain a bit more about thermistors and termocouples?
Did you try to print cold? The feeder motor does not run until you reach a certain temperature in the hotend. This is marlin protection, it does not make sense to run the feeder when cold because you can't extrude. There is a M command that you can give the printer to let the feeder motor run when cold.
Or is it something else...
would you please explain a bit more about thermistors and termocouples?
Try wikipedia! It's a fantastic resource for this kind of thing.
The most important thing to know is that if a circuit is designed for thermocouples you can't replace it with a thermistor. And if a circuit is designed for thermistors you can't replace it with a thermocouple. And these only describe 2 types of temperature sensors. There are other types. The UM2 uses PT100 temp sensor. That can handle the high temperatures but needs special circuitry.
An analogy: Some cars run on gasoline. Some on electricity. You can't just put gasoline on an electric engine and expect it to work.
Dear gr5,
thanks for your answer ,as Zoev89 guide me I'm not using the thermistor with the circuit on the head of the printer(they wont work together as you mentioned in your analogy) ,actually I eliminate the circuit and directly connect the thermistor to the UM. and as you can see in the marlin builder there is multiple options for using 100k thermistor ! but I wonder why you said it's not good and will malfunction in high temperatures :-| I want to know if it's not good I switch back to thermocouples and circut board that I have .
It really depends on the thermistor. For example the E3D hotend comes standard with a 100k thermistor and it can handle up to 295 degrees according to the manufacturer. I don't know if you have a detailed spec of yours. If so it should be specified.
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gr5 2,267
There is a small circuit board on the print head. There are 3 wires. One is ground - should be 0V. One is 5V power. The third reports back the temperature to the board underneath the UM. It should report 0V for 0C and 5v for 500C and 200mV for 20C (room temperature). Measure that voltage and make sure it is correct.
You may have a bad thermocouple or the little board on the head could be defective also.
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