MAXREFDES99#: MAX7219 Display Driver Shield

Figure 1. The MAXREFDES99# reference design block diagram.

Detailed Description of Hardware

See Figure 1 for a block diagram of MAXREFDES99#.

MAXREFDES99# can be powered from a wall-wart which provides a minimum of 7W of power and an output voltage in the range of 7.5VDC to 12VDC. 7W is enough power for the display, plus the microcontroller platform being used through the VIN pin of the target platform. The reference design can be optionally powered from a USB port while developing application code, however, the user must take care not to exceed the power capabilities of the 5V rail supplied by their platform. The recommended method of powering MAXREFDES99# is through a wall-wart connected to J1.

MAXREFDES99# uses the MAX3390E level translator to provide a 3.3V logic-level compatible interface to the four MAX7219 display drivers when using the shield with 3.3V platforms. The serial interface between the platform and the shield uses D10, D11, and D13 for LOAD, DIN, and CLK respectively. The four MAX7219 display drivers are daisy-chained connected with D11 connected to U3 and DOUT of U3 connected to DIN of U4 and so on. DOUT of U6 is left unconnected.

Detailed Description of Firmware

Libraries have been developed for both Arduino platforms and the online development environment mbed.org which supports microcontrollers from several manufacturers of ARM Cortex^®-M microcontrollers. The source code for these libraries and their corresponding 'Hello World' demo programs can be found in the design files, or at the following links.

• Arduino
  • GitHub Link
• mbed
  • Library
  • Demo Program

Figure 2 provides a high-level flow chart of the demo program for both platforms.

Figure 2. Demo program flowchart.

Quick Start

Required equipment:

• Windows® PC with a USB port
• MAXREFDES99#
• MAX32600MBED or Arduino® UNO Development board
• 7W (min) Wall-Wart with 7.5VDC to 12VDC output

Procedure

This reference design is fully assembled and tested. Follow the steps below to verify board operation.

1. Connect MAXREFDES99# to the user supplied Mbed®/Arduino platform.
2. Connect wall-wart power adaptor to J1 of MAXREFDES99# and switch the sw1 to the arrow pointing position to turn on the display
3. Connect a USB cable from the PC to the platform.
4. Follow the appropriate instructions below:

1. Arduino
   1. Download the library from the GitHub repository
   2. Extract the MAXREFDES99-master.Zip library file
   3. Open the Arduino IDE, version 1.6.7 or later.
   4. In the tool bar, go to "Sketch" and select "Include Library"
   5. Select "Add .ZIP Library…"
   6. Go to the folder where you extracted the Library
   7. Open folder RD99_ARDUINO_V01_00 and select MAX7219
   8. Navigate to File/Examples/MAX7219/MAXREFDES99_example
2. Mbed
   1. If you have never used Mbed, setup an account and add your platform to your online compiler per the instructions on your platform's product page.
   2. If you are using Windows and have never used serial communications between your PC and your mbed platform, follow the instructions.
   3. Navigate your browser to this link.
   4. Click the 'Import this program' button and import the demo as a 'program'
3. Compile and download the resulting binary to your platform.
4. Open HyperTerminal, or your favorite terminal emulator, find the appropriate COM port for your platform, and configure the connection as following
   1. Arduino - 115200bps, 8-N-1 with no flow control
   2. Mbed - 9600bps, 8-N-1 with no flow control
5. Ensure your terminal settings are configured for 'Auto' on Receive and 'CR+LF' on transmit.
6. Press the reset button on your platform and exercise the demo.
7. When running endless loops on the display, press the reset button on the platform to stop the loop and return to the main menu

Arduino is a registered trademark of Arduino LLC.
ARM and mbed are registered trademarks of ARM Limited.
Cortex is a registered trademark of ARM Limited.
Windows is a registered trademark and registered service mark of Microsoft Corporation.