Testing A 191 Thermometer + Ridding The World Of 9-Volt Batteries

I bought one of the Hakko 191 knockoff thermometers. And it worked. It's nice to have an easy way to check the soldering iron tip temperature. So I take a look inside the beast. And decide that the 9-volt battery has to go. So now it’s a knockoff 191 thermometer with a rechargeable battery. It's a fun project all around.

Thermometer link: https://a.co/d/dSlreMn

00:00 Intro
01:18 Setup
02:47 Tip Temperature Testing
05:01 A Look Inside
06:03 9-Volt Replacement Selection
07:33 Part Selection
09:42 Circuit Design
13:08 PCB and Parts Assembly
14:33 Setup and Testing
17:19 Making It Fit
20:00 Fixing an Error
21:46 Exploring the ATtiny412 Setup & Code
26:48 Final Thoughts