After burning through my fourth cheap soldering iron, I decided it was time for something more professional. At the time I was soldering on an increasingly frequent basis and needed to do work on a robotics project that suffered from the lack of temperature control in the simple devices I had used in the past. Building a custom digital soldering iron seemed like a good opportunity to kill two birds with one stone:
- Create a powerful and accurate soldering tool that can be used for future projects.
- Gain more experience in the fields of electronics, 3D printing and prototyping
This project was finished in two stages, because it got shelved for a year after it hit about 80% completion. The hardware might not be entirely up to par any more, but the design certainly stands!
The design is based on readily available (clone) parts, predominantly from China. At the start of this project only a few soldering controllers were available and most open source projects were still a work in progress. The chosen controller works with Hakko T12 tips, which perform well (70W) and are easy to interchange in the soldering handle. An interesting feature is that the thermocouple is placed in series with the heating element; the heating wire is one half of a Nickel-Nichrome (or -Kanthal) thermocouple which simplifies the design and frees up wires.
The design of the controller is a combination of hits and misses. It is feature rich (4 quick temperature settings, auto-sleep functionality, rotary encoder input, 16×2 display included, on board NTC) and has good specifications where it counts. However, the board layout is not great, it lacks proper documentation and the pin spacing on the DC input and DC output are terrible.
With the help of topics on dangerousprototypes.com and datasheets the basic workings are uncovered. Board logic power is regulated by a TI LM7805 which is rated for 25V. The controller utilizes a FDS 4953 Dual MOSFET with maximum ratings of 30V and 5A. It is a P-channel MOSFET to keep the ground connected at all times. During each cycle the controller switches between powering the heating element and reading the value of the thermocouple.
The controller is fed with 24V DC. Mains power is supplied via an IEC 320 socket with a built in fuse holder and switch. In runs through a large 24V 120VA toroidal transformer and is rectified by a KBU 1010 rectifier. A 4700uF capacitor is used to decrease the voltage ripple. The 5A 180 KHz XL4015 buck DC/DC converter by XL Semi provides regulated power to the controller. The power train performs very well and delivers a stable 24V without getting hot.
The Chinese FX-9501 Hakko clone has sub par quality, but it has some usable components. For this built, the T12 connector, the lower part of the handle and the strain relief have been reused in the new design. An eight pin GX16-8 lockable connector is used to connect it to the soldering station.
The soldering station features a bespoke design tailored to the hardware components it needs to house and personal preferences. Its main components are a modified aluminium enclosure and a PLA 3D-printed base that ties everything together. Except from the wiring, the entire design was modelled in Solidworks.
The display is tilted to provide better visibility to the user and prevent it from getting obscured by the rotary encoder and/or the cable that runs to the soldering iron.
A large knurled aluminium knob provides improved tactility and adds a more qualitative feel to the design. The recessed placement relative to the extrusion enclosure keeps the footprint of the station smaller and also provides some protection in case of an unintentional drop.
The PLA base is made specifically to limit the amount of post-processing needed to assemble the soldering station. The toroidal transformer is mounted on ribs that closely follow its shape. The number of ribs are increased near the centre to improve stiffness where it is fastened to the base. There is no space to mount the large capacitor securely on a PCB, so a cradle is incorporated in the design. It is held in place by a lid that doubles as a mount for the buck converter. The electronics and the encoder are mounted on strips of bare FR4 boards, to drastically increase the stiffness in those areas as compared to incorporating them into the 3D print. To keep the design as clean as possible, dovetail rails are incorporated into the print to mount the aluminium enclosure. It is held in place by screwing on the original rear bezel.
The base has two chamfered corners that can be used to mount the socket for the soldering iron. In this case it is mounted on the right hand side, because I am left-handed; the soldering station is positioned to the left to keep the workspace clear.
The Hakko logo does not use the vertical leg of the second “K” in the brand name and it resembles a stylized letter “C”. The spoofed logo used in my design switches the two and gives the project its name: “Hacko”.
The original (clone) soldering iron handle has been reverse engineered with the goal of creating a custom handle with an improved design. The new handle has a more spacious design to create room for thicker wiring and a vibration (sleep) sensor, while still maintaining a sleek appearance. The knurled surface improves the feel of the handle and gives it some texture which helps to mask the (FDM) layers of the 3D printed part.
One of the key features of the new design is that it is made from thermochrome filament. The colour of the handle actually changes from brownish black to milky white when the soldering iron becomes hot!