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A weight based measurement of the number of cups of coffee currently available in the kitchen.
A set of bathroom scales lives underneath the coffee machine in the kitchen, connected to an Arduino Ethernet that measures the weight, calculates the number of cups of coffee in the machine and sends the data out to Xively. All the measuring electronics of the scales has been bypassed and the Arduino measures the mass of the water in the coffee machine by reading resistance change from the strain gauges at each corner of the scales, via an INA125 instrumentation amplifer. Detail on connecting the instrumentation amplifier to the Arduino is shown in the ArduinoInstAmp repository in GitHub.
A remote monitor for the scales polls the Xively feed regularly for the latest values of the number of cups and displays the results on a dial gauge in the main room of DoES. While it is possible to find out the amount of coffee available from anywhere there's internet access, the usefulness of the information diminishes as you get further away from the machine. The optimum condition for using the CoffeeBot would be out-of-sight of it, but still in the same building.
While collection of the level of the coffee in the machine is an interesting exercise and it's nice to know if there's coffee available before getting up, there are some more practical uses once the data has been collected. Averaging the number of cups consumed during each day might give guidance on when to stop making coffee in the afternoon, and how many cups to make in the last pot. Tracking total cups made would mean that it's possible to determine how regularly coffee beans need to be purchased so as to keep them available, but still fresh.
Up-to-date and historical information on DoES's coffee usage is available at xively.com/feeds/106284.
Setting the Empty Weight
There is now a tare (zero) button on the board, with a red LED. To zero the scales:
- Take both pots off the coffee machine (doesn't matter if they're full or empty).
- Press the tare button.
- Wait for the red LED to come on, this may take a moment of it's in the middle of sending data.
- Wait 2 seconds for the red LED to turn off. ''Don't touch or knock the machine during this time, this is when the measurement is taking place''
- Place the pots back on the coffee machine.