Wireless charging for a HP-25 calculator

[jwr]

Hi fellow HP enthusiasts,

I thought you might enjoy my weekend hacking project. I decided I should do something to make my HP-25 usable every day. So, I set out to design a rechargeable battery pack, which replaces the original one, but uses a modern Li-Po battery, and has Qi/WPC wireless charging with a USB fallback. I now have the perfect engineering calculator, that is 45 years old and yet sits happily on a Qi power pad and recharges. If I don't have a pad available, I can remove the battery pack and use the micro-USB connector in the side to charge it.

For more details: https://partsbox.com/blog/wireless-charg...-2021.html