Building a Calculator
My first job after university was designing analogue circuits and programming their firmware. I skipped larger through-hole and went straight to SMD (Surface-mount Devices). These were tiny devices that required using a magnifying glass and tweezers to solder. I learnt a lot at that job. Shortly after, I switched to doing software, and haven’t really touched a soldering iron since. I figured building a DIY calculator kit would be a fun project to do with my 7 year old over the holidays, and it only took a couple of hours to build. I plan on doing this again with my other kids, and with more complicated circuits as my kids get older. My son already had a simple calculator, but I think he’ll appreciate it that much more knowing how the internals are put together. You can pick it up at Amazon for around $18 (link).
We did this in the garage, as I wanted to not have anyone walking around near the soldering iron.
I had my son do everything except the soldering. He selected the parts and connected them to the circuit, and then handed the calculator to me for soldering.
I even had him use a multi-meter to confirm he was using the correct parts.
My 4 year old even wanted to help out.