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Unformatted text preview: ED displays, the common anode type and the common cathode one. In the common anode type, VCC (diode’s anode pin) is shared. This shared pin is set to ‘high’, whereas the other pins from ‘a’ to ‘g’ retain active ‘low’ – i.e., ON for 0, OFF for 1. Conversely, Ground (diode’s cathode pin) is shared in the common cathode array. Thus, the shared GND pin is set to ‘low’, while the other pins from ‘a’ to ‘g’ are active ‘high’. Figure 4.2.1 is an example of the common anode 7-segment LED display. Here, a NPN transistor is used for the ‘power control input’ that is a device to control the power for the 7-segment LEDs. For Over-Current Protection, a resistor of 330 ohm is connected to the collector. Besides, a resistor of 2.2K ohm is connected to the base for high input impedance. Electrical supply is controlled by sending varying levels of current from the base. That is, if the ‘power control input’ device is ‘high’, the current flows through. Otherwis...
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- Spring '10