Serial 4-digit seven segment LED display
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. It's based on MAX7219 LED display driver.
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 (0.40Ē size) and two colon segments (to support time display) display.
The main controller of this display module is MAXIMís MAX7219 driver chip. Included on-chip are a BCD decoder, multiplex scan circuitry, segment and digit drivers, an 8×8 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.ís
LTC-4727JS module, which has LED segment arrangement and pin
configuration as shown in figure below.
click on schematic for full resolution
This display module can be easily interfaced with Arduino using the
LedControl library. Hereís an example that displays numbers 1 through 4
and activates the L1, L2, and L3 segments. The SPI interface pins DIN,
CLK, and LOAD of MAX7219 are driven by Arduino digital I/O pins 7, 6,
and 5 respectively in this example. However, the LedControl library
allows customization of these pins.
3D PCB rendering
- MAX7219 datasheet: http://datasheets.maximintegrated.com/en/ds/MAX7219-MAX7221.pdf
- Arduino LedControl library: http://playground.arduino.cc/Main/LedControl
- PIC12F683 and MAX7219 interface: http://embedded-lab.com/blog/?p=4935
- Buy 4-digit MAX7219 based displays: https://www.tindie.com/products/rajbex/spi-4-digit-seven-segment-led-display/
- Buy 8-digit MAX7219 based displays: https://www.tindie.com/products/rajbex/spi7segdisp856-kit-eight-digit-serial-spi-seven-segment-led-display-red/
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