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  • A fully automatic coffee bean roaster (Arduino)

    You could use a pressure sensor at the fan outlet. This should give you a reasonably steady state signal between the two flow regimes for static beans (higher pressure), and fluidised beans (lower pressure). I'm not sure if the relationship will be linear, but there will be a relative pressure drop (pressure over fan speed) once the beans fluidise. You could slowly increase fan speed until you notice a step change in pressure.

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