| 摘要 |
A meter dial register encoder employs a plurality of photoresistor sensors in a row and column matrix configuration. A microcomputer selectively scans the photoresistors to determine whether they are illuminated or non-illuminated. Each column of the row and column matrix contains a scanned photoresistor and a plurality of unscanned photoresistors operated in a two-or-three-out-of-five code, with one terminal of the scanned photoresistor being selectively connected to a 5 volt source by a microcomputer, the other terminal of the photoresistor being connected to the column conductor. The unscanned photoresistors of the column are connected between the column conductor and a separate terminal of the microcomputer held at ground potential. The column conductor is supplied to one terminal of a two terminal comparator, the other terminal of which is connected to a source of reference voltage. The photoresistors of each column thus comprise a voltage divider circuit, the output of which is monitored by the comparator. The unscanned photoresistors of each column serve as a reference for the scanned photoresistor, allowing the use of photoresistors having much greater variation in illuminated on resistance state while providing an accurate determination of whether the scanned photoresistor is illuminated or non-illuminated. |
