Sharing damn simple cheap alternative to expensive Hakko FG-100 thermometer

[mcinque]

Nothing particularly fancy or complicated here, something that even a monkey can do...

Instead spending $$$ for the overpriced Hakko FG-100 to check solder irons calibration, I guess it's damn cheap (and damn easy) to use this kind of pcb and a meter with K thermocouple input and purchase only the cheap 191-212 hakko sensors.

I found this way better than simply using a K thermocouple on the iron tip because the Hakko sensor is much more stable and I can get repeatable readings and the sensor thermocouple is housed inside a small metal cage to avoid adding metals to the bimetallic junction while measuring tin temperature, falsing the readings.

- connections are made with 1.8mm RC battery contacts (females are soldered to the pcb, males are used to "hold" the Hakko sensor, the sensor height is optimal)
- pcb is attached

Maybe someone can find this useful, even if it's so damn simple that anyone can do it.

[GreyWoolfe]

Why not get a Hakko FG-100 knockoff?  Under $12 USD from China.  They even work fairly well.  I have one.

https://www.ebay.com/itm/FG-100-Soldering-Iron-Tip-Thermometer-Temperature-Tester-LCD-Display-0-700-DIY/192691374192?hash=item2cdd4d0870:g:iUIAAOSwGWJcUW1S:rk:3:pf:1&frcectupt=true

[mcinque]

Why not get a Hakko FG-100 knockoff?

Mostly because of calibration: you can't calibrate some versions as they are manufactured by different "companies" each one with a different PCBs inside, attached examples, one is without calibration. Since I can't know which kind of fake I'm buying, and since I already have a digital thermometer with K thermocouple input, I preferred to choose this way.

EDIT: maybe you can add calibration to the second pcb by adding VR1 but I don't like this kind of incertainess and the crappy soldering and flux residues.

[amyk]

The temperature-voltage dependency of a thermocouple is exact, that does not need calibration after it leaves the factory.

[mcinque]

Indeed, but the voltmeter reading the thermocouple value won't require a basic calibration? Mostly because we're reading millivolts.