I haven't touch anything like this in a good while, how cheap could I get a simple Arduino style chip with a few gpio to drive a yellow LED in 2025?
For £3.50 you can get an ESP32 module with WiFi and Bluetooth (e.g. https://thepihut.com/products/esp32-c3-mini-development-boar...)
(A regular Arduino board might still be the best choice if you're just learning/tinkering though)
At this cost for a hobbyist it's just hard to beat. It can be anything you want it to be in a few lines of code.
I personally write Rust for it, not Arduino C++, but it would work just the same.
I've got dozens of them in my electronics drawers I don't really use anymore since ESP32 dev boards are so cheap and capable for home projects.
Granted, you can almost get a microcontroller for that price…
Kind of mind-blowing. 24mhz 32-bit computer for under a dime.
But you'll learn more about the analog-ish world and not need to deal with SMD if you go the 555 route. And it'll save you power vs the astable monovibrator with NPN transistors.
Make has a really nice little book where they walk you through some simple projects on a breadboard with 555s, transistors, etc. https://www.amazon.com/How-Use-Breadboard-Make-Handbook/dp/1...