PID Temperature Controller

My friend is building a plastic extruder for plastic recycling (https://preciousplastic.com). He needs to control the extrusion temperature. For that purpose he is using a nozzle heater band. In this nozzle, there is a thermocouple and a heating unit which allow us to measure the temperature and finally reach the desired temperature (make a retroaction loop).
When I heard that he needed to by several PID controllers to control all these nozzle heater bands, it immediately gave me the desire to try to make our own.”

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