Dust Extraction Panel

An 800 x 480 panel by the workshop door, pressed with gloves on - so the targets are large and there is nothing small to hit. The gates are on a PCF8574 rather than on the board, which is what you do when the panel is by the door and the gates are across the shop: one pair of wires instead of four runs. The extractor starts itself when any gate opens and stops when the last one closes, so nobody has to remember. A differential pressure sensor across the filter drives the bar, and an analog threshold puts up the cleaning banner - which is a more honest service interval than hours run, because a filter blocks at the rate the work dirties it. The motor hour meter is persisted, so it survives a power cut.