Arduino MAX7219/7221 Library Written by Eberhard Fahle in 2007 Refactoring, cosmetic changes and hardware SPI by Radu - Eosif Mihailescu <radu.mihailescu@linux360.ro> 2012-04-13 Bug spotting in 7-Segment example by John Williams <mrjtwill at yahoo.com> 2012-06-27 AS1100/1106/1107 support by Radu - Eosif Mihailescu <radu.mihailescu@linux360.ro> 2012-07-19 To the furthest extent that this is legally possible, the fork maintained by Radu - Eosif Mihailescu and published here https://github.com/csdexter/MAX7219 is hereby released under the LGPL version 3. To the furthest extent that this is legally enforceable, the copyright remains with the authors listed above. See the example sketches to learn how to use the library in your code. HARDWARE NOTES: * The AS1100/1106/1107 is pin-for-pin compatible with the MAX7219/7221. They do have a bit of extra functionality in register 0xE which can also be accessed with this library. Apart from that, they behave identically to the MAX7219 so everything explained here and in the examples about the former, equally applies to the AS1100/1106/1107. * The MAX7219/7221 are 5V I/O driver chips that power their loads from the digital 5V rail. This means you will need to find another power supply to feed the MAX if you plan to use more than one of them (the power regulator on the Uno/Mega can take 1 MAX + a 64 LED matrix, but not more). This also means a lot of noise will be induced in the digital domain of your project if you don't take appropriate measures by installing the two filtering capacitors shown in the datasheet. * This also means level shifters will be needed if you want to talk to the MAX from a 3.3V I/O Arduino. As the MAX7219/7221 is a SPI device which you may want to drive fast, you may find the majority of level shifters on the market inappropriate because they are designed for I2C which doesn't go faster than 100kHz in most cases. A quick and dirty solution is to use a 74HCT125 quad-buffer instead (which adds quick-disconnect as a bonus). The datasheet specifies its minimum Vhigh voltage as 2V which is more than enough when using 3.3V logic and its maximum speed is above 25MHz so it's well suited for solving the problem at hand. * Quick connection reference: MAX7219/7221 -> Arduino: DIN -> MOSI (Arduino output) CLK -> SCK (Arduino output) LOAD/#CS -> SS (Arduino output) MAX7219/7221 -> LEDs: for 7 segment -> digit 0 is the leftmost one (MSB) and digit 7 is the rightmost (LSB) for 16 segment -> digit 0 on chips 0 and 1 is the leftmost display (MSB), digit 7 on chips 0 and 1 is the rightmost display (LSB) for 14 segment -> as for 16-segment, above for bar graph -> column 0 is the leftmost one, dot 1 (the one that lights up when you write a value of 1 or when you call zeroDisplay()) is the bottom one (wired to SEGG) for matrix -> pixel (0, 0) (the one that lights up when you write a value of {0x01, 0x00, ...} or when you call zeroDisplay()) is the top right one (wired to DIG0, SEGG). Directly under it we have (0, 1) (accessed by writing {0x00, 0x01, 0x00, ...}), wired to DIG1, SEGG; directly to its left we have (1, 0) (accessed by writing {0x02, 0x00, ...}), wired to DIG0, SEGF. For chaining MAX7219/7221s: DOUT(n) -> DIN(n+1) (MAX7219 output to MAX7219 input) DIN(1) -> MOSI (Arduino output) CLK(*) -> SCK (Arduino outputs, may require a buffer if you go LOAD/#CS(*) -> SS past the sinking capability of the Arduino) addressing -> chip 0 is the one closest to the Arduino LIBRARY NOTES: * Due to the fact that we usually work with displays made up of a collection of MAX7219 digits as opposed to single digits, this library uses the concept of topology elements. All data display methods operate on said topology elements instead of single digits. Of course, controlling each individual segment of each individual digit (while at the same time being able to refer to each discrete digit) is still possible if you declare your topology to be a collection of matrices, each one spanning a single digit. In so doing, each topology element gets mapped to a MAX7219 digit and offers direct access to its component segments. * The topology pointer passed to begin() is only being read from and thus declared and treated as const. * The default topology consists of a single element: one 8-digit 7-segment display. * All topology elements can span chips (i.e. you could have a 4-digit 7-segment display made up of the last two digits of chip 2 and the first two digits of chip 3); with the sole exception of MAX7219_MODE_NC which must also end on a chip boundary due to the way scanning limit is implemented in the chip. All topology elements must be contiguous (i.e. you can't have the first and the last digit on chip 0 make up a 2-digit 7-segment display). * All data display functions take a pointer to the data to be displayed as a parameter. The length of data read from that pointer depends on the size in MAX7219 digits of the target topology element; for example a set7Segment() call targeting a 4-digit topology element will attempt to read 4 bytes. For general questions and updates on this library please contact the fork maintainer at <radu.mihailescu@linux360.ro>.