FG-100 Soldering Iron Tip Temperature Sensor


I picked up this cheap soldering iron temperature sensor. I mostly wanted it to check the heat capacity of the various tips I have. I was disappointed that it came with Hakko branding, the supplier just listed it as an FG100 (which is a Hakko model number) but it’s clearly fake.

It does however work pretty well, and I was able to see clear differences between my T12-D12 (1.2mm) tip and T12-D24 (2.4mm). I’ll be performing further tests to see how well the various tips perform and see if I can more accurately gauge the heat capacity of the tips. I also want to use this to check the calibration of cheap Hakko 936 clones that I’ve been picking up from Shenzhen for running workshops.


T12-D24 Tip


T12-D12 Tip

It comes with a set of 10 K-type thermocouples, in order to insure good heat transfer the soldering iron tip should be wet with solder when you measure the temperature. This unfortunately means the thermocouple can get mucky pretty quickly which is why it’s a replaceable part.

Obviously I’ve also taken the device apart too. Below you can see a couple of pictures of the PCB. It uses a single sided PCB with a die on PCB blob. I’m guessing this is a generic temperature sensing IC.


It’s interesting that the PCB has a soldermask, this seems to be a more recent trend with these ultra-cheap single sided PCBs which are commonly used in toys and other low cost products. If you’d like to buy this, I have it in my shop, with the Hakko branding removed. By purchasing from me you support further hacks. In particular I think it’s likely that you add a calibration pot (VR1 on the silk) and fahrenheit mode for people of this disposition.