T12 soldering iron made by sHMIctrl smart screen

The T12 white light soldering iron is also a very classic project in electronic DIY, so much so that the T12 white light DIY soldering iron is also a standard tool for enthusiasts and professionals; the entire circuit of T12 can be said to be a standard temperature control system, so this system is slightly modified , you can realize various thermostat solutions;

In this example, we did not use an auxiliary microcontroller to implement it, but concentrated all functions on the six expansion ports E1~E6. Because E5 and E6 can have PWM functions, the entire function does not require an extended microcontroller at all.

Since the thermocouple is a nonlinear sensor, when designing this project, the main system also specially upgraded the corresponding statements for the nonlinear sensor to facilitate quick table lookup to obtain calculated values;

Related information download:

How to use the fool update package:

• Download t12_rom.zip and copy the extracted firmware.bin and rom.bin files to the root directory of a TF card.
• After powering on, you can see the progress bar for upgrading the firmware (do not cut off the power when upgrading the firmware, otherwise it will easily become a brick) and upgrading the ROM data;
• After the upgrade is completed, the demo data changes to the interface of the soldering iron. At this time, the functions of the soldering iron can be used, and the TF card can also be removed;

Basic circuit design ideas

sHMIctrl has six expansion ports, which can cover input, output, AD, PWM and other ranges. So we found that we can directly use these 6 expansion ports to achieve T12 control without using an auxiliary microcontroller, so we compiled these 6 Port expansion plan:

In the first issue, we first implement the basic function of the soldering iron, namely heating control, and sleep, NTC and buzzer will be implemented slowly later.

Circuit implementation:

Heating part:

PWM signal controls MOS to heat the soldering iron tip

Soldering tip thermocouple signal amplification:

A standard operational amplifier circuit amplifies the signal about 200 times

Power supply part:

Anything below 40V can be input and converted to 5V for use by the screen and microcontroller. C12 has a reserved pad.

For all schematics, please see: https://lceda.cn/zhqsoft/shmictrl-28-t12

Actual PCB and connection method

The position of ESP12s is reserved in the picture. In theory, it can be made into an IoT soldering iron, but it has no practical use and is just reserved.