The first step is to grind the copper clad laminate with sandpaper to remove the oxide layer, and use a marker to draw the lines of the raindrop sensor board

The second step is to put the board in the prepared potion to corrode

Now half corroded and the water is starting to turn a little blue (this was taken about 45 minutes later)

Corrosion completed.... It can be seen that the copper sheet can no longer be seen

The third step is to use sandpaper to remove the black lines after drying (you can use alcohol)

The fourth step is to drill (use a small homemade electric drill, 1.0 drill bit)

The fifth step is to solder the raindrop sensor board to the leads

The sixth step is to weld the buzzer module, the active buzzer is used here

Finally connect the raindrop sensor board and buzzer board together