3.3V conversion for CH340 Arduino Nano clone
A lot of modules I use with an Arduino use 3.3V, not 5V. Here's how to convert a cheap CH340-based Nano clone to run on 3.3V.
This is a little one-page application for calculating all things to do with frequency, impedance, resonance. RC, LC, RL networks, all calculated and graphed in real time.
A high-gain RF probe for a micro-volt meter
The complete simulation and design files for a 16dB high-impedance probe amplifier. You can tweak the input resistance and gain with one resistor each. The structure of the actual probe tip limits its performance providing 16dB gain flat to beyond 300MHz. A smaller tip would allow it to reach closer to the simulated performance, flat to 800MHz.
A LiFePO4 battery pack refit for a Ryobi drill
This nice drill would have been chucked because the batteries are dead.