Embedded within the Da Vinci extruder nozzle is a small temperature sensor.
The obvious function of the sensor is to measure the extruder’s temperature. However, I’d like to know if the Da Vinci printer uses this temperature sensor as feedback to control the heating of the extruder or whether the sensor just functions as a safety cutoff.
To understand the properties of this sensor some investigation work was undertaken. The consensus on the internet is that the sensor is a thermistor but there are few details other than that.
With a few spare components some details about the thermistor have been determined. The process that was undertaken to gather these results is detailed.
The thermistor uses a 2-pin micro-JST plug to connect to the circuit board within the extruder assembly. Note, that it is the bottom of the two micro-JST plugs on the extruder, the top plug is for the cooling fan.
Attempt 1 – Measuring whilst in service
The initial thoughts were to measure the properties of the temperature sensor whilst it was in service. So, using a spare JST plug and socket, a small temporary cable was made so I could insert a multimeter in the circuit without having to damage the thermistor connection.
The plug and socket were soldered together and polarity of the plugs were maintained in case the temperature sensor was polarity dependent. The temperature sensor had not been confirmed as a thermistor yet.
Using IC-test-clips, a multimeter was able to be inserted in parallel with temperature sensor.
Next the small test lead with IC clips was installed in the printer.
Then using the printer’s “Clean Nozzle” utility function, it was expected that as the nozzle began to heat measurements could be read straight off the multimeter. Internet research suggested that the temperature sensor was a thermistor, so the multimeter was set to Ohms. However, as the nozzle increased in temperature and got to operating temperature the multimeter read “0.00 ohms” for the entire process.
Anyway, it dawned on me that it is not appropriate to measure the resistance of a device whilst it is in operation and it wouldn’t work. Why? The extruder’s measuring circuit would likely be calculating the thermistor’s resistance by measuring the voltage drop across the thermistor. By adding a multimeter in parallel, a second voltage is being placed across the thermistor and this would interfere with the extruder’s measuring circuit and cause the multimeter to be interfered with. Anyway, pretty stupid move.
Attempt 2 – Substitute Resistances
Another method of determining the thermistor’s characteristics was devised. This method uses the printer’s “Monitor Mode” to display the extruder’s current temperature. The extruder’s thermistor would be disconnected and known values of resistance would be substituted for the thermistor and “extruder’s” temperature could be read directly from the LCD. This method determines the characteristics of the thermistor indirectly, however it is better than nothing.
An example is shown below. A 270 ohm resistor has been substituted for the thermistor and the extruder’s temperature is shown to be 227 degrees Celsius.
For curiosity’s sake, if the thermistor is disconnected, the display will read 10 degrees Celsius. This may be useful in the future if the thermistor ever fails.
To understand the entire temperature range of the thermistor, multiple values of resistance were substituted and the temperature displayed on the Da Vinci’s LCD was recorded. A multi-turn precision trimpot was used to generate all the values of resistance.
Only the measurements for the extruder when it is in “hot” range are shown in the above graph. However, all the recorded data is stored in a spreadsheet that can be downloaded for your reference – Extruder_data_rev1 . You’ll find that the data suggests that the ambient resistance of the thermistor is 100k ohm.
Analysis of the data confirms that the Da Vinci 1.0’s extruder temperature sensor is an NTC thermistor.
Extruder Over-temperature Fault 0014
For reference, the maximum extruder temperature that was able to displayed on the LCD is 270 degrees Celsius. It appears that if the Da Vinci measures an extruder temperature of at least 270 degrees Celsius for more than 30 seconds, then the Da Vinci goes into fault. (For an extruder temperature of 270 degrees Celcius use a resistance of 84ohm.)
According to the Da Vinci user guide, Fault code “0014” is “The temperature of extruder reach warning range limited”. What I think they mean is, “The temperature of the extruder has reached the warning range”. Anyway when this happens, the printer needs to be turned off and back on again to clear the fault.
For more ways to improve your Da Vinci prints, check out the Tips and Tricks page.