Analog and Digital Heater–Stirrers- Design & Fabrication

Overview
Based on the success of my first 500 °C programmable heater–stirrer, I was asked to design a simpler, robust heater–stirrer system . The goal was to provide controlled heating. I built two versions using a similar mechanical platform but different control approaches:

An analog heater–stirrer with simple knob-based control
A digital heater–stirrer with precise electronic temperature and speed control

Both systems shared the same hot-plate and enclosure design, but targeted different levels of cost, precision, and user interface.

1. Application and Requirements

The main requirements were:

A flat, robust hot plate suitable for beakers and small containers
Integrated stirring capability to mix molten or semi-molten material
A compact metal enclosure with easy-to-use front-panel controls

2. Shared Mechanical Platform

For both analog and digital versions, I used a similar mechanical design:

A rectangular metal enclosure to house all electronics and the motor
A machined aluminum heating block as the core of the hot plate
A stainless-steel top plate bolted to the aluminum block to provide a clean, durable working surface
A motor and magnetic stirrer mechanism mounted underneath to drive the stir bar in the container

This modular approach allowed me to change the control electronics without redesigning the entire device.

3. Analog Heater–Stirrer Version

The first version focused on simplicity and low cost:

Heating was controlled using an analog thermostat / temperature controller and a power control circuit (e.g., triac/relay).
The temperature setpoint was adjusted via a front-panel knob, with indicator lights showing heater status.
Stirring speed was controlled using a separate analog speed controller for the motor, again with a dedicated knob on the front panel.
The wiring, fuses, and switches were arranged on an internal panel to keep the system safe and easy to maintain.

This version was ideal for users who needed a straightforward, “set-and-use” heater–stirrer without complex programming.

4. Digital Heater–Stirrer Version

The second version upgraded the control system to a digital interface, while keeping the same mechanical layout:

A digital temperature controller (or microcontroller-based board) measured temperature via a sensor under the hot plate and regulated heater power precisely.
The front panel included a digital display showing both the actual temperature (PV) and the target temperature (SV).
Users could set the temperature and adjust stirrer speed using buttons or digital controls, giving more repeatable and accurate settings than the analog version.
The motor speed control was integrated into the same board or coordinated with it, providing a defined RPM range for the stirrer.

This version was better suited for applications where temperature accuracy and reproducible conditions were more critical.

5. Assembly, Calibration, and Use

For both units:

hot plate, motor, enclosure, and control electronics assembled
temperature response, heating rate, and stability at different setpoints has been tested
The final analog and digital heater–stirrers provided flexible options for plastics processing: one focused on simplicity and robustness, and the other on precision and reproducibility.

Heater stirrer