7-segment, 4-digit LED module w/ backpack, (ADA: 878)

[last updated: 2020-09-15]
go to: 7-segment LED home page

Adafruit 877 - backpack driver
Adafruit 865 - 0.56" 4-digit 7-segment display

go to: used in - compost temperature meter
go to: used in first prototype of - wall clock/timer
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This module (Adafruit: 878) is the 7-segment, 4-digit module (Adafruit 865)
plus the backpack control module (Adafruit 877)
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Adafruit 878

Adafruit 878

backpack connection pins

• The standard 4-digit, 7-segment LED module has 14 pins (see: 7-segment LED module). This makes it I/O-intensive to implement, so Adafruit and others have a "backpack" module that attaches to the back of the LED module and provides an i2C interface that only requires 4 pins (power, ground, data, & clock) to address the LED module digits.
• The I2c address for the module is configurable with on-board jumpers. There are three jumpers, open by default, but can be bridged/shorted. They're labeled: A0, A1, and A2. If they're open, they have a value of 0, and if shorted, a value of 1.
  Default address is 0x70. Final address is 0x70 + A0 + (A1 * 2) + (A2 * 4)
• In order for it to compile, I had to install the Adafruit LED Backpack Library, as well as the Adafruit GFX Library

• Writing data to the display:

Initialize display with: clockDisplay.begin(0x70);
      ("clockDisplay" is your choice of names for this instance of the display)
Writing to the display requires 2 commands:
      First: write to the buffer, with a variety of command options as listed below,
      Then: flush the buffer to the display with:
            clockDisplay.writeDisplay();

• Write the whole display at once:
• This writes an integer with println:
  clockDisplay.println(1234);
• This writes 4 hex characters:
  clockDisplay.print(0xABCD, HEX);
• This writes a decimal integer:
  clockDisplay.print(1234, DEC);
• This writes a floating point number:
  clockDisplay.print(45.03);
• Write one digit at a time:
• If writing digits directly, the left-most digit is digit '0', colon is '2', and right-most digit is digit '4'
• This writes a single integer to a specified digit (digit '0' in this example):
  clockDisplay.writeDigitNum(0, 9);
  
• This writes an integer bitmask into (eg.) digit '0':
  clockDisplay.writeDigitRaw(0, bitmask);
  • The bitmask is calculated:
    segment 'A' = 1
    segment 'B' = 2
    segment 'C' = 4
    segment 'D' = 8
    segment 'E' = 16
    segment 'F' = 32
    segment 'G' = 64
    decimal point 'DP' = 128
  • So for example to write segments 'A'. 'B', 'F', and 'G', a small circle in top half of the digit that might be used to signify a temperature "degree" symbol,
    bitmask = 1 + 2 + 32 + 64 = 99
    clockDisplay.writeDigitRaw(0, 99);
• This clears/blanks (eg.) digit '3':
  clockDisplay.writeDigitRaw(3, 0);
• This writes the colon:
  clockDisplay.drawColon(true); Turn it off with "false"

eof