If you have a dust collector you know what a pain it is if the shavings backup into the filter. Some of the commercial detectors available are expensive and they rely on an optical sensor. Who would put anything optical inside a drum full of statically charged dust and shavings and expect it to work reliably?
Using Eagle, the PCB I designed determines when a dust collector drum is full by detecting when a small DC motor driving a paddle inside the drum slows down due to shavings restricting the paddle.
How it works:
There is no on/off switch on the board, a switching power supply that powers the board is connected to the dust collectors motor control relay. The board is only active when the dust collector is running. You have to turn the dust collector off to empty the drum so the board is reset by turning the dust collector off and on.
The mcu used is an ATtiny84A. The mcu monitors the voltage drop across the motor driving the paddle within the drum. When the voltage drops below a predefined level the drum is full.
When the drum is full:
- The motor in the drum is turned off using a N-channel MOSFET. The design includes a flyback diode in parallel with the motor to provide a dissipation path for the energy stored in the motor at the moment that its turned off.
- A strobe light is activated using another N-channel MOSFET.
- (optional) A message is sent using an RFM69CW transceiver. Noted as optional because the board works with or without the RFM69CW transceiver installed.
If a message is sent, the message is received by a companion board I designed that will send the message Dust collector full to my hearing protector that has a built-in FM radio. See https://www.instructables.com/id/Audio-Alert/
The board contains a DC-DC module to supply 5V power to the motor and to a 3.3V regulator on the board that powers the mcu and the optional transceiver.
The overall board is powered by an AC 120-220V to 12V DC switching power supply. The strobe is a 12V device.
Reliability:
I initially thought that the paddle would be in the way when emptying the drum and eventually it would snap off. Ive been using it for over a year and because of its location on the drum cover, the paddle stays out of the way. I use it on a wall mounted dust collector. The drum on my collector is on wheels. The cover is light, it lifts up and you move the drum out from under it. I dont think this solution would work well on a portable dust collector where you lift the motor attached to the drum cover off in order to empty it. You would need to devise some way to protect the paddles when placing the cover on the floor.”

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