This is a project of an alternative SH72 soldering iron controller with turbo mode, two-stage sleep mode, grounding the soldering iron tip to a "-" power wire and the protection against the reverse polarity, short circuit and overvoltage.
In normal mode, the upper output of the temperature regulator R1 (according to the schematic diagram) is connected to the +5V net, and the lower one to the ground net. In turbo mode, when the SW2 button is pressed, the lower output of the regulator is connected to the +5V net, due to which the maximum temperature of the soldering iron tip is set, regardless of the position of the temperature regulator.
If for some time the position sensor did not change its state (closed / open), and the turbo mode was not used, then the upper output of the temperature controller R1 is connected to the ground net, due to which the minimum temperature of the soldering iron tip is set regardless of the position of the temperature regulator (sleep mode).
Exit from this mode to the normal one can be done by shaking the soldering iron (the position sensor will change its state) or by pressing the turbo mode button. If, for some time after entering sleep mode, the position sensor does not change its state and the turbo mode button is not pressed, the soldering iron will enter the power down mode, in which the power of the soldering iron tip will be completely turned off by the transistor VT1. Exit from this mode to the normal one can be done by pressing the turbo mode button or by the power reset.
The original circuit was taken as a basis, additional functions were implemented on the ATtiny13 microcontroller. Thanks to this, when upgrading the soldering iron, most of the components for this controller can be taken from the original board. Due to the use of components from the original circuit, some of them had to be located on the bottom side of the board due to lack of free space on the top side.
Protection against the reverse polarity, overvoltage and short circuit is implemented by the fuse FU1 and suppressor VD3.
When ordering board, you should choose the FR-4 core with a thickness of 1.2 mm.
Due to the lack of free space on the board, the programming connector was not installed. Therefore, it is necessary to program the microcontroller before installing it into the board or connect the programmer cable by soldering it to the following pins: 1 - RESET, 4 - GND, 5 - MOSI, 6 - MISO, 7 - SCK, 8 - VCC.
Warning! Be careful when powering the MCU from a programmer or external source, as the MCU power is shunted by a parallel voltage regulator (DA1, 5V)! Also during the programming of the MCU, the position sensor (SW2) should be disconnected and turbo button (SW1) should be released!
Despite the fact that the DA1 stabilizer on the original board is marked as 431, its pinout corresponds to the 432. Based on this, the DA1 stabilizer is marked in the diagram and installed on the board as 432.
The firmware of the microcontroller was designed in such a way as to use the factory-setted fuse bits, only the flash memory of the programs needs to be flashed in the new MCU. The firmware repository can be found here.
At the moment, the board and MCU firmware have been developed, but not tested yet, since the boards have not arrived from the factory yet.