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Calibration

A project log for ChaiBot

Tea Steeping robot that starts a timer when cups are filled with hot water and lifts bags automatically to make perfect tea every time.

adrianAdrian 04/03/2016 at 10:560 Comments

The capacitive load sensor readings can be monitored and a detection threshold set for cup sensing (both for auto timing & auto shutoff) by entering "test mode". This is performed by pressing the paddle switch and holding it down until TEST appears on the display. A reading of something around 1000 should be expected without any weight on the cup base and the value should go up as cups and water are added (or you simply press down on the base).

While in test mode, turning the rotary encoder will alter the stored threshold setting. This value defaults to 200 but can be adjusted to suit the build. This threshold is used in two places:

  1. After empty cup(s) are placed and the gantry is lowered, the capacitive reading (weight) is noted. The threshold is now used to detect the pouring of hot water to automatically start the timer. I.e. weight has increased.
  2. When steeping has ended and the gantry is automatically raised, the threshold is used to determine when the cup(s) have been removed. I.e. weight has decreased.

Because of 2. a three-second delay has been introduced before the gantry is lowered following cup removal detection to allow time for both cups to be removed. A possible refinement would be to use the weight increase (as measured between the point when the empty cup reading was taken, and at the time when steeping terminated) and only perform auto shutoff when more than half this weight was removed.

To exit test mode (and as general rule to shut down the device) press and hold down the paddle.

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