alt Hacker NewsBad programming. People who have experience with embedded programming knows that reading out a button usually means denouncing. At the speed a microcontroller can read out a button it will change it's state multiple times per press because of contact bounce. Meaning when a user presses a button the program sees off, on, off, off, on, on, off, on, on, on, on, on, on, etc.
Now if you just naively read out the current state of the button and do something with it elsewhere in the program looping may be off or on randomly.
It is not hard to imagine if there is some other logic (or e.g. a rate limit) on the 30 seconds and on the beep that these would see different slices in time of the button. Congrats you built a button-debounce based RNG.
Physical buttons can be surprisingly complex if you don't rely on someone else's driver. The correct solution is to debounce the button, that can be done either in hardware (too expensive, so rarely done) or in softeare, by e.g. averaging the last 50 reads and wait till the majority is either off or on.
This should be common knowledge for embedded programmers, but every noe and then you will see someone who has never heard of it.
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Checking the button state a bunch of times and computing an average wastes a ton of clock cycles that you could be doing anything else (like updating a display, polling sensors, etc).
The standard way to debounce is to attach an timer to the button. When you press the button, an ISR runs that temporarily disable the timer from triggering again and starts the timer for a specific period (say 20ms). The processor is free to do whatever it wants for the next 20ms. When that timer expires, another routine checks to see if the button is still being held, sets the button's state accordingly, then re-enables the button Timer so it can be triggered again.
Averaging loops are much better for analog inputs where you may have noise that throws off the reading. You only care about a button being on or off, it doesn't matter if it's been mostly on for that period only that it's still on.
When you get into extremely fast digital inputs that need to be reacted to sooner than the debounce wait period, that's when you need hardware debouncing.
> People who have experience with embedded programming knows that reading out a button usually means denouncing
I know you mean "debouncing" but I love the autocorrect. Like the button is some almighty authority that Denounces noisy signals.
>averaging the last 50 reads and wait till the majority is either off or on.
This is a bad way to do it because it adds avoidable latency. A moving average is a low-pass filter. The switch bounce is better handled by hysteresis. Change state as soon as you see an edge, then ignore further edges until a timer expires, e.g. 5 ms, which should be enough for the bouncing to settle. A 5 ms timeout limits your repetition rate to 100 presses per second, which is beyond human capabilities.
You might want a tiny bit of hardware low-pass filtering too, for EMI resistance, but that's with microsecond-scale time constant, not milliseconds.