With some exceptions, projects aren't necessarily "beginner" or not in some intrinsic sense. What makes it "beginner" or "expert" is related to the details of the requirements and constraints. Building water level sensor to do something for your goldfish? Probably trivial. Building a water level detector that needs to be guaranteed to be accurate and stable enough to control the pumps and valves rigged up to a 10,000,000 gallon storage tank that serves an entire county? Perhaps more of a challenge.
Take the function generator idea: you can go order an
XR2206 chip and a few passive components and have a "function generator" in less than an hour. But build a lab quality function generator that can compete with something like the
Keysight 33622A and now you're talking about a whole different ball of wax.
So I think the people saying "start with a domain that interests you" are on the right track. If everything interests you, flip a coin or use an RNG to pick. Then start with the simplest project you can do in that domain that won't bore you to tears, then start working out how to advance your $WHATEVER to have better specs, more capabilities, be more reliable, run at a faster frequency, be easier to use, etc., etc.
I mean, hell, my
most recent project was turning a desk lamp on and off with a relay and an Arduino. Not exactly rocket science, right? But the point isn't just to turn a lamp on and off... that's a building block to do more stuff. Now I can look at adding a motion detector and make a simple security system. Or I can start working on voice recognition so I can make my own Alexa-like thing that can turn the light on and off at my command. And I can extend the basic ideas to something other than a light - maybe I want to turn a water pump on and off that's watering some potted plants on the deck out back. And maybe I'll jam a moisture sensor in the pot and try to automate the watering so I don't forget. Blah, blah, blah, etc.. the point is just that something can start "simple" and then become more complex as you add stuff to it or add constraints ("it has to be light enough to send to Mars", etc.)
Have fun. And I hope your goldfish survives!
