Egglift: an automatic LEGO egg cooker

Step 3 Detecting the position of the basket:

To obtain a reliable cooking system, it is relatively important the lower (and less importantly the upper) position of the basket remains constant and precise: the eggs have to be fully submerged in the boiling water for a safe cooking.

The choice of a temporization in the program (turn on the winch for 5 seconds before turning it off) would have not been well suited for this application.

Because of inaccuracies in the motor, in the gear train and the weight variation of the eggs, to basket would have not returned to the same place every time.

The position of the basket can be detected with a light sensor aimed at the black-and-white circle on the left stuck to a 40-tooth wheel.

This wheel has 24 divisions, alternatively black-and-white. When the motor that control the basket is on, the light sensor counts how many divisions had passed by, thus letting know the RCX a fairly accurate representation of the position of the basket.

This method is not too accurate, but it is accurate enough for this type of application.