Using LEDs, LCDs and GLCDs in Microcontroller Projects

10.5 PROJECT 10.5 – External Interrupt Based Event Counter Using 4-Digit 7-Segment LED Display with Serial Driver

10.5.1 Project Description

In this project, a display module known as the BM08M04N-R is used. This is a 4-digit 7-segment LED display manufactured by Nexus Machines Ltd. This is a family of 7-segment displays ranging in size from 8 to 38 mm and available in colours of red, green and yellow. The project counts events occurring on external interrupt pin RB0/INT0. An event is said to occur when the state of RB0/INT pin goes from logic 0 to logic 1. This project is similar to Project 10.4, but here the event is interrupt driven and also the display is a 4-digit 7-segment LED module with serial driver.

The BM08M04N-R display (see Figure 10.19) has an on-board controller chip that accepts data in serial format. The display has 9 pins, as shown in Table 10.1. 36 bits of serial data are sent to the display where a logic 1 turns a segment ON. The display has two pins (pin 1 and 2) where external LEDs can be connected via on-board current limiting resistors. The cathode of the external LEDs should be connected to these pins, and the anodes to the Vledpin (pin 9). The chip enable pin (pin 3) should be LOW for the display to be enabled. The brightness pin (pin 7) provides the segment brightness. A resistor is provided on the board that can be used, or an external resistor can be used to provide the required brightness. Serial clock pin (pin 5) clocks data into the display on the ...