DIY Build a Low-Cost 1321 Soldering Iron Control Board

If you are interested in DIY soldering iron controller boards, you may want to take a look at this article.

If you notice that the Xinghe XH-W1122 temperature control board uses a MOSFET to control the output instead of a relay, you will find that the MOSFET is rated at 6A, but the temperature control range is only 0–100°C. It uses an NTC3950 10K thermistor for temperature measurement, which means it cannot directly control a 1321 soldering iron core. If you happen to have suitable firmware, you can modify the board to control a 1321 soldering iron core.

When you measure the 1321 soldering iron handle, you will find that the heating resistance is about 4 ohms and the temperature sensing resistance is about 49 ohms. If you heat it up to 500°C, the sensing resistance increases to around 149 ohms. This indicates that the sensing resistance is still too low (much lower than the 10K of the NTC3950), so if you want to obtain a readable voltage for the microcontroller ADC conversion, you need to use an operational amplifier for signal amplification. You can refer to the following modification steps:

Solder the temperature sensing amplification circuit for the 1321 soldering iron core. This is the circuit diagram.

The actual setup is shown in the figure below.

Flash the firmware to the control board.
The W-1122 temperature control board already exposes the programming interface, as shown in the figure below.

The left side is negative, the right side is positive, and the middle pins are the clock and data lines. You will need a programmer to download the HEX file.

Modify the W1122 temperature control board.
After flashing the firmware, the original NTC thermistor will no longer be usable. Before connecting the amplification circuit, you also need to modify the control board by removing a 10K SMD resistor shown in the figure below.

After removing it, you also need to tap a 5V positive supply, which can be taken from the right pad of that resistor. This voltage will be used to power the operational amplifier circuit you soldered earlier.

Connect the power supply, temperature control board, and soldering iron handle for testing.
You must ensure that your soldering iron uses a 1321 heating core. If it uses a 1322 core, it will not work.

If you test temperatures at 200°C and 300°C, you will observe a temperature drift of about 2–3°C. When measured with a 191 soldering iron thermometer, the temperature error is within 10°C. Of course, each 1321 soldering iron core may vary, so this range cannot be guaranteed for all units.

Finally, the modification is complete.