First soldering irons are often of the
Radioshack or Maplin firestarter variety. They’re basically wall power shorted across a nichrome heater or similar with some inline resistance to make it harder to burn down the house. You plug them in, the current flows, and they get hot. Done.
If you stick with the hobby for a while, these eventually get replaced with something like the venerable HAKKO FX-888D or that one Weller everyone likes with the analog knob. These are much improved; having temperature control leads to a more consistently heated tip and much improved soldering experience.
Entering the electronics workplace one comes across the next level of quality soldering iron: high end HAKKOs, Metcals, JBCs, and the like. Using one of these irons is practically a religious experience; they heat in a flash and solder melts while you blink. They even turn off when you put the handpiece down! But they’re expensive to buy (hint: think used). What’s a hobbyist to do?
[SergeyMax] seems to have had this problem. He bit the bullet, figured out how the Metcal works, and made his own base. This is no mean feat as a Metcal might look like a regular iron but it’s significantly more complex than ye olde firestarter. The Metcal magic is based on a oscillating magnetic fields (notice the handpiece is connected via BNC?) interacting with a tip bearing a special coating. In the presence of the changing field the tip heats up until it hits its Curie temperature, at which point it stops interacting with the magnetic field and thus stops heating.
When the user solders, the tip cools by sinking its heat into the part and drops below the Curie temperature again, which starts the heating again. It’s like temperature control with the sensor placed absolutely as close to the part as possible and a nearly instant response time, without even a control loop! [SergeyMax] has a much more thorough description of how these irons work, which we definitely recommend reading.
So what’s the hack? Based on old schematics and some clever reverse engineering from photos [SergeyMax] built a new base station! The published schematic is as rich with capacitors and inductors as one could hope. He didn’t post source or fab files but we suspect the schematic and photos of the bare board combined with some tinkering are enough for the enterprising hacker to replicate.
The post contains a very thorough description of the reverse engineering process and related concerns in designing a cost efficient version of the RF circuitry. Hopefully this isn’t the last Metcal replacement build we see! Video “walkthrough” after the break.