Tonight's work will be another live-stream, hacking on F3l1ks. After the 3D Printer extruder PEEK insulator meltdown, it seemed prudent to verify that the temperatures, shown and logged by octoprint are actually the temperatures of the bed or the hot-end.
In theory it works like this: The Bed and the hot-ends have so called thermistors built-in, which are, in simple terms, just a certain kind of resistors that change their resistance (in ohm) proportional to their temperature. A specific temperature will result in a specific and predictable resistance. When we know the linearity and parameters/curve of the thermistor we can use the ADC of any uC to measure the Voltage which will change proportionally with the resistance. With a little math we can convert the digital value back to °C. So far my understanding of the principle and could/should also be reviewed in the Firmware code (reminder).
Theory is all good, but in theory the PEEK element also never should have melted. But it did. Now it's time to gather and verify data to make sure it wasn't some error in the firmware configuration, wiring or setup that led to instrumentation errors, where the temperature readouts actually were much lower than the actual temperatures to reach way above 245°C to melt the PEEK. So let's wire up an external thermometer with a K-Type temperature sensor and verify the data of the bed and the hot-end thermistors through the whole chain:
Thermistor → Cable → Connector → ADC → Firmware → USB → OctoPrint → VFCC
Since the cam and metrics shipping is already in place you can follow it live: