SS3-Power

SS3 — Solder Station 3

A DIY Weller-compatible soldering station controller, inspired by the kair.us Weller WMRP and WMRT compatible soldering station.

Overview

SS3 is a two-board redesign of the kair.us open-source solder station. The key differences from the original are:

• Transformer-based power supply instead of SMPS — cleaner, simpler, lower EMI
• Native 12V and 24V tip support — handle type is identified by reading a resistor inside the handle via a voltage divider (510Ω for WXUP, 1kΩ for WMRP, 2kΩ for WMRT)
• MSPM0G1507SRHBR MCU (Texas Instruments) replacing the PIC16F1788
• Dual MOSFET back-to-back switching stage acting as a solid-state triac with minimal conduction losses

Hardware — Two Boards

MCU / Display Board

Handles all control logic, ADC measurements, and user interface.

• MSPM0G1507SRHBR microcontroller (default)
  • MSPM0G1505SRHBR can be used for 7-segment display builds
  • MSPM0G1506SRHBR can be used for TFT display builds
  • Switching variant requires updating device_linker.cmd
• Onboard ADC for thermocouple sensing (cold-junction compensation is handled inside the handle itself)
• Display support:
  • 4× 7-segment LED display
  • 1.9" TFT color screen

Power Board

Drives the resistive heating element of the tip.

• Four dual N-MOSFET ICs (8 MOSFETs total), one per heating channel: two channels (left/right) × two voltages (12V/24V), each pair wired back-to-back
• Each pair acts as a solid-state triac equivalent, covering both 12V and 24V channels
• Lower switching losses compared to a traditional triac

Tip Compatibility

Compatible with Weller active tips using an integrated heater and thermocouple:

• WMRP — soldering pen (12V)
• WMRT — desoldering tweezers (12V)
• WXUP — soldering pen (24V)

Directory Structure

SS3/
├── 3D/       — Stands and handle models (12V and 24V variants; no enclosure provided)
├── PCBS/     — KiCad / Gerber files for both boards, plus KiCad conversions of the
│              original kair.us WMRP and WMRT boards (including mirrored variant for
│              mirrored jack barrels)
├── SIMS/     — LTSpice simulations: zero-cross detection, 3.6V SMPS from half-wave
│              rectifier, and back-to-back N-MOSFET triac equivalent
└── SS3/      — Firmware source (CMake project)

Credits

Based on the open-source Weller WMRP and WMRT compatible soldering station by kair.us.