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thermistor_troubleshooting [2016/04/16 16:24] – [Check Thermistor Wiring] Traumflugthermistor_troubleshooting [2018/05/27 16:10] (current) – external edit (unknown user)
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   * //CT1// means to smooth out noise, it's not directly involved in the measurement circuitry.   * //CT1// means to smooth out noise, it's not directly involved in the measurement circuitry.
   * //Connector// is where the thermistor is connected.   * //Connector// is where the thermistor is connected.
-  * //RT1// makes up a [[https://en.wikipedia.org/wiki/Voltage_divider|voltage divider]] together with the thermistor.+  * //RT1// makes up a [[https://en.wikipedia.org/wiki/Voltage_divider|voltage divider]] together with the thermistor. Most controllers have a 4700\_ohms resistor here, which gives optimum resolution at about 100\_°C. 1000\_ohms moves the range of optimum resolution closer to typical extruder temperatures.
  
-Connecting components this way gives a voltage on the signal line which depends on the thermistor's resistance and accordingly, on the thermistor's temperature. If the thermistor is very hot, its resistance is near zero, so the signal's voltage will be close to zero. If the thermistor is very cold resistance is very high, signal's voltage will beclose to the supplied voltage, 3.3\_volts (or 5\_volts on other controllers). In between is our measurement range.+Connecting components this way gives a voltage on the signal line which depends on the thermistor's resistance and accordingly, on the thermistor's temperature. If the thermistor is very hot, its resistance is near zero, so the signal's voltage will be close to zero. If the thermistor is very coldresistance is very high, signal's voltage will beclose to the supplied voltage, 3.3\_volts (or 5\_volts on other controllers). In between is our measurement range.
  
 ===== Hardware Measurements ===== ===== Hardware Measurements =====
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 Before searching for firmware misconfigurations, it's always a good idea to check hardware. A firmware can only report the voltage on the processor's signal pin. Before searching for firmware misconfigurations, it's always a good idea to check hardware. A firmware can only report the voltage on the processor's signal pin.
  
 +==== Thermistor Type ====
 +
 +Actually, thermistor type doesn't matter much for troubleshooting. They all work by the same principle, so the circuitry shown above always works (unless it's broken). Most RepRap printers use thermistors with 100\_kOhms nominal resistance. This means they have 100\_kOhms at 25\_°C ("room temperature").
 +
 +During firmware configuration types matter a lot more, because there we want not only a working principle, but also reasonably accurate readings.
 ==== Check Supply Voltage ==== ==== Check Supply Voltage ====
  
-Easiest way to do this is to disconnect the thermistor and measure voltage between both pins. With no thermistor connected, it should be full supply voltage, 3.3\_or 5\_volts depending on the controller.+Easiest way to do this is to disconnect the thermistor and measure voltage between both pins on the board. With no thermistor connected, it should be full supply voltage, 3.3\_or 5\_volts depending on the controller.
  
 ==== Check Thermistor Wiring ==== ==== Check Thermistor Wiring ====
  
-This measurement is simple, too. Disconnect the thermistor and measure resistance between both pins. At room temperature this should be around the nominal value of the thermistor, typically 10\_kOhms or 100\_kOhms. Warming the thermistor by hand should reduce this resistance.+This measurement is simple, too. Unplug the thermistor connector and measure resistance between both pins there. At room temperature this should be around the nominal value of the thermistor, typically 10\_kOhms or 100\_kOhms. Warming the thermistor by hand should reduce this resistance by a few kOhms.
  
 Measuring the thermistor while it's plugged in gives false results. Measuring the thermistor while it's plugged in gives false results.
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 ==== Check Voltage on the Processor Pin ==== ==== Check Voltage on the Processor Pin ====
  
-This is what the firmware actually "sees", so it's crucial.+{{ :troubleshooting:gen7_2.0_thermistor_measurements.jpeg?direct&300|Location of thermistor pins on a Gen7-ARM 2.0}} 
 + 
 +This is what the firmware actually "sees", so it's crucial. Picture to the right shows where these pins are located on a Gen7-ARM 2.0. It's the 5th and 6th pin in the upper row. 
 + 
 +This measurement can be done without the processor installed. If one is installed, the firmware shouldn't make these pins an output, but keep the default, input. 
 + 
 +Without a thermistor connected, both pins should read full 3.3\_volts (5\_volts on 5\_V controllers). Connecting a thermistor at room temperature (not to these processor pins, but to the thermistor header on the board) should drop this not much, but a bit. Typically to 3.1\_... 3.2\_volts. 
 + 
 +Warming the thermistor by hand might change that slightly, perhaps by another 0.05\_V drop. Warming the thermistor with a lighter or soldering iron (be careful to not overheat it!), should drop that voltage further, down to very low readings, like 0.5\_V.
thermistor_troubleshooting.1460816677.txt.gz · Last modified: 2018/05/27 16:10 (external edit)