Last year we had a thread where the problem of knowing when the bin on the dust collector is full, I suggested a paddle the gets slowed by the rising dust level.
Here is my first go at this solution.
The paddle is rotated by a small 12v motor at 5rpm.
The small power supply has resistor in series with the motor and when the voltage across the resistor increases, the sounder and LED are turned on.
It is still in a trail phase, I will keep an eye on it, I think I might need to add a couple of blades to the current paddle, if the bin is a bit too full when it sounds the alarm.