Volume 2 · Number 1 · February 1982

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Three lines are used as Inputs. Two input signals come from the level switches which indicate when the drum is full and empty. As shown in figure 2, these switches are connected to +5 V. through 10 Kohm pull up resistors.


The third input is used by the processor to determine the speed of the drum for feedback purposes. A reflective optical switch points at the metal spokes of the pulley which turns the drum. When a spoke goes past the switch light is reflected and a ‘1’ is generated on the P.I.O. input line, which is usually at ‘0’. The circuit requires a transistor amplifier to step up the output from the receiver to TTL level for the P.I.O.


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