Connecting Current Limiting Resistors to a Cluster of 8 Seven Segment Displays?

          We had already seen the criterion for connecting current limiting resistors to LED matrix. Same criterion have to be followed for connecting current limiting resistors to a cluster of 8 common cathode seven segment displays. We had reduced the number of control pins, for a cluster of 8 common cathode seven segment displays in previous blog. Current limiting resistors can be either connected to the anode terminals or to the cathode terminals. Current limiting resistors of 100 ohm are connected to the anode terminals (a, b, c, d, e, f, g and dp) as shown in the following circuit.

          To get maximum brightness, each segments of seven segment display should have separate resistors. Since only one seven segment display will be on at a time, if resistors are connected to the anode terminals (a, b, c, d, e, f, g and dp), each segments will get separate resistors. So segments will light up at maximum brightness. At the same time, if separate resistors are connected to the cathode terminals of seven segment display cluster, when a particular seven segment display turns on, resistor connected to the cathode terminal of that seven segment display will become common to all the anode terminals of that seven segment display which will reduce the brightness of that seven segment display considerably. From these, we can conclude that, current limiting resistors should be connected to the anode terminals (a, b, c, d, e, f, g and dp).

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