Книга: Advanced PIC Microcontroller Projects in C

PROJECT 6.6 — Two-Digit Multiplexed 7-Segment LED 

Project Description

This project is similar to Project 6.5, but here multiplexed two digits are used instead of just one digit and a fixed number. In this project the number 25 is displayed. In multiplexed LED applications (see Figure 6.29) the LED segments of all the digits are tied together and the common pins of each digit are turned ON separately by the microcontroller. When each digit is displayed only for several milliseconds, the eye cannot tell that the digits are not ON all the time. This way we can multiplex any number of 7-segment displays together. For example, to display the number 53, we have to send 5 to the first digit and enable its common pin. After a few milliseconds, number 3 is sent to the second digit and the common point of the second digit is enabled. When this process is repeated continuously, it appears to the user that both displays are ON continuously.

Figure 6.29: Two multiplexed 7-segment displays

Some manufacturers provide multiplexed multidigit displays, such as 2-, 4-, or 8-digit multiplexed displays, in single packages. The display used in this project is the DC5611EWA, which is a red 0.56-inch common-cathode two-digit display having 18 pins and the pin configuration as shown in Table 6.9. This display can be controlled from the microcontroller as follows:

• Send the segment bit pattern for digit 1 to segments a to g

• Enable digit 1

• Wait for a few milliseconds

• Disable digit 1

• Send the segment bit pattern for digit 2 to segments a to g

• Enable digit 2

• Wait for a few milliseconds

• Disable digit 2

• Repeat these steps continuously

Table 6.9: Pin configuration of DC56-11EWA dual display

The segment configuration of the DC56-11EWA display is shown in Figure 6.30. In a multiplexed display application the segment pins of corresponding segments are connected together. For example, pins 11 and 16 are connected as the common a segment, pins 15 and 10 are connected as the common b segment, and so on.

Figure 6.30: DC56-11EWA display segment configuration

Оглавление книги