Since I got a bigger place where I can have a projects area slash lab slash dumpster I have been upgrading the basic tools needed to get the job done.
One of the most valuable tools is a proper soldering iron, and since many years ago I have been a fan of the JBC irons. Since I first tried one at work I wanted one for myself.
Now a JBC soldering station goes for a minimum of about 400EUR which due to my cheap nature and limited budget makes it as available as unobtainium. The JBC handles on the other hand go for about 50EUR and I was sure I could get one used for free.
Thinking about the controller itself I pondered about designing something from scratch, order the pcb, sourcing the parts, assembling them, discovering the routing errors made at 2am while working with only one eye opened…
So I went the quick and dirty way, searched aliexpress for the cheapest piece of kit which kind of made what I wanted, and had the possibility of being improved upon with some custom firmware.
The problem with the solution
I found a controller made for the popular hakko T12 tips , featuring an STM32 (which I have quite an experience with), an Oled display (never used one but since they are cheap I can use the learning experience for the future) and a rotary encoder. Schematic was no available but for less than 20USD I couldn’t go wrong.
Judging by the product picture to the right I was somehow convinced that the original firmware was garbage, the
Chinese characters, and the fact that the only understandable writing was “error” may have had something to do with that idea.
With the plan strongly defined on ether I asked my wife’s permission to spend 30EUR and ordered myself one of these controllers, an hakko T12 handle and a couple of tips so I could test without ruining a much more expensive JBC tip.
The solution to the problem with the solution
After about on month a orders arrived and I quickly tested them, not surprisingly it didn’t work very well, with a set point of about 300ºC the pour T12 tip became red hot, which, even not being a soldering iron PhD, I don’t think should happen at that temperature.
Time to reverse engineer the controller schematic. For that I used my favorite technique of taking pictures of both sides of the board, opening them with gimp, assigning them to different layers, reversing the bottom layer, adjust skew and size so they perfectly overlap, and play with the top layer transparency so I can see what connects to what.
Time to start drawing the schematic while annotating the image with some info.
This was what I came up with:
An SWD connector so it will be easy to flash and debug, a DC-DC converter with an input of 4.5V to 28V, an exotic amplifier circuit for the thermocouple, a not so fast mosfet and driving circuit for the heating element, a buzzer, voltage input sensing trough voltage devides, ntc for ambient temperature sensing used for cold junction compensation, a bunch of passives, and a…hum…thing with a voltage reference going to an ADC pin (no idea, something to do with neutrinos protection probably).
Eagle file will be available from the github project soon.
Eagle file link
EDIT:Most of the passive values of the schematic are made up, I would have to remove them from the PCB for proper measurements, and it doesn’t really matter for what I’m trying to accomplish.
With the schematic at hand I will start writing the firmware for this thing, next post will be about the development environment and project setup I use for such a thing and the 3rd and final post will be presenting the finished firmware.