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.<br /><br />Thermometer link: <a href="https://a.co/d/dSlreMn" target="_blank" rel="nofollow">https://a.co/d/dSlreMn</a><br /><br />00:00 Intro<br />01:18 Setup<br />02:47 Tip Temperature Testing<br />05:01 A Look Inside<br />06:03 9-Volt Replacement Selection<br />07:33 Part Selection<br />09:42 Circuit Design<br />13:08 PCB and Parts Assembly<br />14:33 Setup and Testing<br />17:19 Making It Fit<br />20:00 Fixing an Error<br />21:46 Exploring the ATtiny412 Setup & Code<br />26:48 Final Thoughts