Summary of A simple temperature control system (for 3D print or other constant temperature control purpose)
Summary: The author built a standalone temperature control system for a 3D printer hot end using a power resistor heater, an N-channel MOSFET switch, and an LM324 quad op-amp. One op-amp acts as a comparator to switch the heater based on a thermistor reading; the other three op-amps scale the thermistor signal to drive a 0–30V voltmeter for temperature readout. The design was chosen to let a Raspberry Pi-controlled printer use an independent analog temperature loop.
Parts used in the Temperature control system for 3D printer hot end:
- Power resistor (used as heater)
- Thermistor (temperature sensor)
- LM324 quad op-amp IC
- N-Channel MOSFET transistor
- 0–30V voltmeter (for temperature readout)
- Supporting passive components (resistors for nominal reference and scaling)
- Power supply capable of driving heater and voltmeter
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After finishing the mini CNC laser engraver, the next thing in my mind is 3D printer. One of the most important part of a 3D printer is the plastic filament extruder, composed by a cold end constantly supplying plastic filament, and a hot end melting the plastic and feeding the liquid plastic through a small nozzle.
For PLA or ABS plastic filaments (most common materials used in home-made 3D printers), the hot end needs to be at a temperature of about 200C (or 180C for PLA, 220C for ABS). It is important to keep this temperature (roughly) constant, so is the plastic melting speed and then a controllable plastic feeding rate.
Therefore two components are essential: a heater, and a temperature sensor. The heater heats up the hot end nozzle, and the sensor monitors the temperature. The heater is on when the nozzle temperature is too low, and is switched off when the nozzle is too hot.
I plan to build a home-made 3D printer controlled by my Raspberry Pi, which, unfortunately, does not have any analog data acquisition pin. Therefore I decide to build a stand-alone temperature control system.
The idea is very simple. I use a power resistor as the heater and a thermistor as the temperature sensor. The system contains an LM324 quad op-amps chip. One op-amp is used as a comparator to compare the thermistor resistance with a nominal resistance and output LOW or HIGH as the comparison result. The other three op-amps inside the LM324 are used to perform some linear transformation and output a voltage that is proportional to the thermistor temperature. This voltage is applied to a 0-30V voltmeter so one can read the temperature. A N-Channel MOSFET transistor is used to control on/off of the heater.
For more detail: A simple temperature control system (for 3D print or other constant temperature control purpose)
- What is the heater in this temperature control system?
The heater is a power resistor used to heat the hot end. - What sensor is used to monitor temperature?
A thermistor is used as the temperature sensor. - How is the heater switched on and off?
An N-Channel MOSFET transistor is used to control the heater on/off. - Which IC provides temperature comparison and scaling?
An LM324 quad op-amp IC is used; one op-amp as comparator and three for linear transformation. - How is the temperature displayed?
The output voltage proportional to thermistor temperature drives a 0–30V voltmeter for readout. - Why build a stand-alone temperature control system?
Because the Raspberry Pi lacks analog data acquisition pins, a stand-alone controller provides independent analog temperature control. - What temperatures are typical for PLA and ABS hot ends?
PLA about 180C and ABS about 220C, with a general hot end target around 200C. - Which op-amp inside LM324 is the comparator?
One of the four op-amps is used as a comparator comparing thermistor resistance to a nominal reference.
