Week no.13
- Input Devvices
Assigments :
- Measure something
- Add a sensor to a microcontroller board that you have designed and read it
Temperature Probe
The idea for this assignment was to add a temperature sensor to control the Heated-Bed temperature for my printer. Since the desired target temperature would range from 80º to 140º degrees Celsius, the first choice was to use a thermocouple type K. And I just got one that ranged -50º to 400ºC
The first problem: I just realized I needed an amplification board for the millivolts signal from the thermocouple. It also needs to compensate the cold junction reference for correct measurement.. – It remembers me the good old days from my first job as an engineer in FullGauge Controls, 16 years ago -- beside it is a lovely project and I would really enjoy doing it with a Wheatstone bridge and some Amp-ops, there was a time problem. I was a little bit late on schedule, that implementation should already be done at this time (25/10/2017) so it will be a future update.
The quick turnaround would be to implement a thermistor carefully chosen for the working temperature range.
Implementing a Platinum Thermistor
I find out that in the FabAcademy Inventory there was a platinum Resistance temperature detector (RTD-PTS12061.0KCT-ND). Nice, just what I needed ! The specs are: Platinum SMD Flat Chip Temperature Sensor.
The idea is to make a 4-wire RTD measurement to reduce voltage drops from wiring, I would suggest this good article about this topic by Measurement Computing.
Thermistor test
So I jumped to a thermistor sensor I had, it´s a replacement part for a commercial refrigerator. I don’t have much information about it but the nominal resistance value of 10k and the Beta parameter, since it is sealed, all I can do is test.
I worked through the Adafruit tutorial, with I strong recommend since it goes thought the testing, filtering and temperature conversion in Arduino. Ando so I made my first test with a Arduino Uno sending the AD reading values trough the serial to my PC.