Thanks. Yeah you’re recommending what I was initially thinking.

You should probably use a simulation tool to check the circuit before you start destroying chips.

Fair!

I work in industrial automation and have a background in pneumatics. I think you’ll be surprised at how inefficient pressurizing/moving air is. I think the most practical solution (if you can call it that) is likely carrying an air reservoir that can be pumped up with a bike pump, and having a valve to trigger the whistle. There isn’t really a safe way to carry compressed air on a bicycle because it’s inherently dangerous to transport. There are lots of ways to make an unsafe air reservoir for example what Chris Notap on you tube does.

If you’re doing it to learn about electronics and physics it’s a great thing to do.

Tinkering is fulfilling in and of itself.

You may be interested in the Kelvin Water Dropper.