This project is a 7 segment LED display module that can be driven using SPI protocol, so it needs only 3 pins of your mcu to drive 4 x LED displays. Itβs based on MAX7219 LED display driver.
Description
Seven segment LED displays are very popular for displaying numeric information because they are very attractive and readable from a far distance and wider viewing angle.
The downside is they are resource-hungry. For example, it requires 12 I/O pins of a MCU to drive a 4-digit seven segment display using a standard time-division multiplexing technique.
Here I present a serial seven segment LED display module that can be used with any MCU using a 3-wire SPI interface. This particular display has four digits (0.40Β size) and two colon segments (to support time display) display.
Β Schematic
The main controller of this display module is MAXIMΒs MAX7219 driver chip. Included on-chip are a BCD decoder, multiplex scan circuitry, segment and digit drivers, an 8Γ8 static RAM to store the digit values, and a 3-pin SPI interface to receive the display data from the host MCU.
The segment current for all LEDs is set through only one external resistor. However, the device also provides a digital control of the display brightness (16 steps from minimum to maximum) through an internal pulse-width modulator.
The seven segment module used in this project is LITE-ON, Inc.Βs LTC-4727JS module, which has LED segment arrangement and pin configuration as shown in figure below.
For more detail: Serial 4-digit seven segment LED display
