As is the case with a lot of the designs I see here, I don’t understand why it has a microcontroller in it. Using a 556 timer (dual 555) could have provided exactly the same functionality in a much more compact, inexpensive and simple design.

As an electrical engineer who is primarily focused on embedded software I tend to be biased toward using microcontrollers wherever they are beneficial, but in a case like this it is obvious overkill. If you’d used a cheap 8-pin micro with an internal oscillator in place of a 556, I’d probably like it, but using a $30 board in place of a $0.50 chip seems wrong.