Pen Solder V3 (PSV3) replacement firmware

Cheap soldering iron reverse engineering and replacement firmware.

See also the write-up on my blog.

Note that while the product is advertised as a T12 soldering iron this is just the name of its ubiquitous soldering tip (Hakko T12). So I needed a more specific name for it and chose the label on its PCB: Pen Solder V3 or short: PSV3.

Replacement Firmware

Development WIP in ./firmware.

Current state (quite usable!):

• soldering tip temperature PID controller code works (adapted from IronOS)
• temperature measurement synced with off time of tip switching PWM
• all buttons work
• voltage measurement of soldering tip temperature and VBUS (from USB-PD) work
• display output works (it's connected to non-hardware-I2C pins, so we're bitbanging with U8g2 with custom STM32 optimizations for around 170kHz I2C clock speed)
• standby after 60s without activity (partly implemented, just turns tip off at the moment)
• no cold junction compensation (not available on this board)
• no settings storage
• resource usage: around 30/32kB flash, 1.4/4kB RAM (we're splurging a bit by including an additional font and Arduino libs)
• supported boards: V3, V7

"Pen Solder V3" Description

Its name is: Portable T12 Electric Soldering Iron PD 65W DC 72W.

Tracing the board layout:

Which leads to this Reverse Engineered Schematic (click for PDF):

"Pen Solder V7"

To compile for V7 boards open ./firmware/platformio.ini and change the following line:

-D PENSOLDER_V=3

to

-D PENSOLDER_V=7

Thanks to @Gobracket for finding the needed change in the display's setup!

Flashing

Some test pads are labeled on the board: VSS, CLK, DAT, VDD:

Connect them to GND, SWCLK, and SWDIO from your STLink adapter respectively. Do not connect VDD. It's cleaner to supply the board in a more stable manner using an USB-C supply instead.

You can then build and flash my firmware from within VSCode using PlatformIO (just press Build/Upload).

Dumping Stock Firmware

Before flashing a custom image you should backup the stock firmware!

I used the Debian 12 package of st-tools for this:

st-flash --hot-plug read t12-f0.bin 0x8000000 32768

Hardware Details

Label on case: T12

PCB:

PEN-SOLDER V3 2023-02-02

MCU: CHIPSEA F030F6P6

• https://www.st.com/resource/en/datasheet/stm32f030f4.pdf
• https://www.st.com/resource/en/reference_manual/rm0360-stm32f030x4x6x8xc-and-stm32f070x6xb-advanced-armbased-32bit-mcus-stmicroelectronics.pdf

$ st-info --probe 
Found 1 stlink programmers
  version:    V2J34S7
  serial:     ...
  flash:      32768 (pagesize: 1024)
  sram:       8192
  chipid:     0x0440
  descr:      F0xx

Big P-MOSFET: NCE30P30K

• https://datasheet.lcsc.com/szlcsc/NCE30P30K_C130106.pdf

Small N-MOSFET driver: 72K

• Maybe: https://pdf1.alldatasheet.net/datasheet-pdf/view-marking/1085166/RUICHIPS/2N7002K.html

OpAmp: 8331CGn04

• https://datasheet.lcsc.com/lcsc/2206101816_Gainsil-GS8331-TR_C157712.pdf

Zener: W3

• Maybe: BZT52C3V3 https://pdf1.alldatasheet.net/datasheet-pdf/view-marking/58974/DIODES/BZT52C3V3.html

SMPS: XL1509-3.3E1

• https://www.xlsemi.com/datasheet/XL1509-EN.pdf

USB: CH224K

• https://datasheet.lcsc.com/lcsc/2204251615_WCH-Jiangsu-Qin-Heng-CH224K_C970725.pdf
• https://www.laskakit.cz/user/related_files/ch224ds1.pdf
• https://components101.com/ics/ch224k-usb-power-delivery-controller-ic

"STM"32F030 Pinout

• 1: BOOT0 -> 10k to GND
• 4: NRST -> filtered VDD
• 6: PA0 -> not connected here, but optionally a non-populated part could connect it to some kind of SMD part (white square with 4 pads)
• 7: PA1 -> ADC: VIN measurement of 1/11*VBUS
• 8: PA2 -> ADC: Temperature measurement of soldering tip's thermocouple (through amplifier)
• 9: PA3 -> Heating enable for soldering tip
• 10: PA4 -> Button "Minus (-)", high active (10k pull-down to GND, button pulls to VDD)
• 11: PA5 -> Button "Plus (+)", high active
• 12: PA6 -> I2C SCL to display (4k7 to VDD)
• 13: PA7 -> I2C SDA to display (4k7 to VDD)
• 14: PB1 -> Button "Set", high active
• 17: PA9 -> looks like it's not connected to anything, used in stock firmware for display reset
• 19: PA13/SWDIO -> SWD header/pads
• 20: PA14/SWCLK -> SWD header/pads

CH224K USB-PD Control

CFG1,2,3 pins are not connected to anything. Floating CFG1 means it will request VBUS=20V from USB power supply. That's a bit concerning given that this means the P-MOSFET gets U_GS=20V (or more) and that's already its U_GSmax.

Too bad those pins aren't connected to the uC or we could switch to a lower USB voltage.

OpAmp

• Used as non-inverting amplifier, 221x gain
• Input connected to T12 soldering tip pin A (the last ring), (tip pin B (the ring between A and Earth) is connected to GND)
• Zener diode clamps input to 3.3V max.
• Input range should be 14.9 mV max. assuming the output is 3.3V max.