DIY T12 Soldering Station: Microcontroller Temperature Control

For those with an interest in electronic craftsmanship, chances are you have accumulated an array of microcontroller-based components such as stc89, stc15, M8, Arduino (atmega), stm8, and more, often left neglected in a dusty corner. Crafting a T12 soldering station has long been a popular topic in online DIY communities. Soldering irons are essential tools for electronic enthusiasts, and if you happen to possess an electronic voltmeter with an stc8h microcontroller, this project is well worth exploring. Furthermore, it provides an opportunity to delve into C51 microcontroller programming for those accustomed to working with Arduino.

Procure a 24V3A power supply to complement your T12 soldering iron. Size isn't a major concern as soldering irons are typically stationary devices.

In theory, a digital control T12 is simpler than its analog counterpart. The operational sequence is straightforward: "Power On - Monitor T12 Temperature (Thermocouple Voltage) - Compare with Set Temperature - If Lower: Activate Heating, If Higher: Deactivate." It truly is that uncomplicated.

With a digital display, you already have a microcontroller equipped with ADC (Analog-to-Digital Conversion), GPIO (General Purpose Input/Output) pins, a display unit, and buttons. Additionally, the current detection circuit typically includes an operational amplifier for signal amplification. These components together comprise the essential hardware for a complete digital control T12 soldering station. The control algorithm for the T12 soldering iron is also relatively straightforward, making it an ideal project for beginners to delve into microcontroller programming. Additional hardware requirements include configuring GPIO pins to control a high-current PMOS transistor for regulating the T12 heating element and integrating the T12 thermocouple voltage into the microcontroller. The primary focus of this project lies in software development.

The simplified diagram illustrates the electronic voltmeter head's functionality: measuring the voltage drop across resistors R5-1 and R5-2, amplifying it using the TP09 operational amplifier at a gain of (1+250/2), and finally, collecting the amplified voltage with the microcontroller's ADC. This voltage is then converted into current values. The essential input is Ain+, responsible for the original current detection, capturing the thermocouple electromotive force from the T12 soldering iron, amplifying it, converting it into temperature values, and subsequently comparing it with the set temperature. The OUT1 pin is utilized to control the heating and deactivation of the T12 soldering iron by toggling between high and low logic levels. Buttons serve the purpose of adjusting temperature settings and selecting various functions.

Create a small PCB (Printed Circuit Board) using a perforated board to accommodate the mentioned circuitry. Port pins are employed for controlling the PMOS transistor (or NMOS, if preferred) to regulate the T12 soldering iron's temperature while simultaneously interfacing with the T12 thermocouple voltage, which is then amplified and read by the ADC. In the diagram, T12+ and T12GND are connected to the positive and negative terminals of the T12 soldering iron, respectively. OP9-Ain connects to Ain+ as shown in the initial diagram, and MCU-IO connects to OUT1. Remove the current-sensing resistors R5-1 and R5-2 and replace R3 and R4 with 300K and 1K resistors, respectively, to achieve a 300-fold amplification.

The hardware components have been successfully configured.

The subsequent step involves the development of software.

The software aspect is equally straightforward. The software used in the original electronic voltmeter head already includes features for display, button input, and ADC data acquisition. Therefore, only minor modifications are necessary.

The process can be summarized as follows, and it is as straightforward as it sounds. In fact, the main control loop can be expressed succinctly in a single line of code: CurTempADC < SetTempADC ? HeatPin = 1 : HeatPin = 0;

After connecting this system to the digital voltmeter, programming the microcontroller, and running tests, it should operate reliably. For those seeking further refinement, options include implementing PID (Proportional-Integral-Derivative) control, creating an elaborate user interface, and incorporating menus for adjusting the soldering iron temperature curve. However, the core functionality hinges on the previously mentioned line of code. T12 soldering irons are inherently stable, temperature fluctuations of approximately 10 degrees Celsius have negligible practical implications. In the absence of dedicated temperature measurement equipment, using ADC values divided by 10 as a temperature display is a viable alternative. Fine-tune the settings through repeated adjustments during usage, observing the CurTempADC value to gauge the desired temperature.

Future enhancements and customization possibilities encompass:

1. Incorporating a vibration switch or reed switch for implementing sleep or automatic shutdown functions.

2. Implementing PID control algorithms, which can regulate either the heating duration or the PWM (Pulse Width Modulation) duty cycle for even more stable temperature control (note that this may present a significant technical challenge).

3. Enhancing the user interface with improved aesthetics and menu-driven settings (consider establishing a versatile framework for microcontroller-based menu systems).

It's worth noting that this project entails both hardware and software components, requiring a solid understanding of electronics and microcontroller programming to execute effectively.