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Parts
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The DHT22 is quite accurate, cheap and easy to use. See here for more details. I chose the model from AZDelivery. It already has the necessary resistor installed and is ready to use. Run it on 5V to get more reliable reading. The good thing about this sensor is that it can read both Temp & Humidity, but only once every two seconds. I am using two sensors and read alternative, so I get read values every second. For best PID control, faster reading would be better and more accurate. So maybe the one-wire DS18B20 sensor might be better, but only reads temperature...
I purchased a simple stepper motor with 1.5A from Stepperonline. See data-sheet in the docs folder. It can be nicely controlled via the DRV8825 driver. Have a look here for a very detailed explanation.
After trying a few, I chose the IRLZ34N MOSFET to control my heating element. It is powerful enough to switch the 150 Watt heater and has a low enough gate voltage to be controlled via the RasperryPi. The 3.3V of the GPIO pins are not enough though to fully switch the MOSFET under load. Therefore a amplify the gate voltage to 5V. Then it runs fine. It gets a bit warm and so I installed a heat sink and 12V mini-Fan on tis back.