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Name: MAX7219
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Author: Gavin Lyons.
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Description: A Raspberry pi library to display data on a 8-digit MAX7219 seven segment module. Dynamic install-able system level Raspberry Pi C++ library. Hardware or software SPI, Shutdown mode, test mode and Brightness control supported.
Example files list:
| List No | Example file name | Description | SPI type |
|---|---|---|---|
| 1 | src/tests_swspi/main.cpp | test sequence | software |
| 2 | src/tests_hwspi/main.cpp | test sequence | hardware |
| 3 | src/bcdmode/main.cpp | Shows use of BCD built-in font | hardware |
| 4 | src/clock_demo/main.cpp | Clock demo , Shows use of cascaded displays | hardware |
| 5 | src/cascade_demo/main.cpp | simple Demo showing use of cascaded displays | hardware |
For Software SPI Pick any GPIO you want. To get the number for GPIO_CHIP_DEVICE parameter you can check ls /dev/gpiochip* At time of testing it was found that Raspberry pi 5 = 4 and raspberry pi 3 = zero But now it look like both are zero after software update, although 4 should still work for RPi5 if a symlink is in /dev/ folder. In software SPI user may need to increase or decrease CommDelay variable (uS Communication delay) depending on speed of CPU on system.
For Hardware SPI the User must use fixed SPI pins SPIMOSI and SPISCLK, user can choice between SPICE0 and SPICE1 for chip select. The Datasheet says it's a 10MHZ device, In hardware SPI user can pick SPI bus speed.
| parameter | default value | note |
|---|---|---|
| HWSPI_DEVICE | 0 | A SPI device, >= 0. which SPI interface to use , ls /dev/spi* |
| HWSPI_CHANNEL | 0 | A SPI channel, >= 0. Which Chip enable pin to use usually 0 or 1 |
| HWSPI_SPEED | 1000000 | The speed of serial communication in bits per second. |
| HWSPI_FLAGS | 0 | mode 0 for this device |
| Pin no | RPI SW SPI | RPI HW SPI | Pin function |
|---|---|---|---|
| 1 | any GPIO output | SPISCLK | CLK = Clock |
| 2 | any GPIO output | SPICE0 or SP1CE1 | CS = Chip select |
| 3 | any GPIO output | SPIMOSI | DIN = Data in |
VCC 5V in theory but works at 3.3V in testing, albeit with a dimmer display. Logic seems to work fine at 3.3V , It safe as it is all one way communications From RPI to MAX. User can adjust brightness from 0x00 to 0x0f by default it is 0x08. 0x0f being brightest
Support for Cascaded Displays is shown in two of examples files. Multiple displays can be connected together. Cascaded Displays are displays connected together. CS and CLK lines are tied together. The DIN line is connected to the first display only. The DOUT line of the first display is then connected to the DIN line of the next display and so on. Diagram below shows how to connect two displays together. Specify number of displays in constructor parameter.
