Sunday, May 7, 2017

Programming the MeinEnigma - Display LEDs

The four alphanumeric LEDs on the MeinEnigma are controlled by the HT16K33 chip in a similar fashion to the discrete LEDs. The only difference is visual: the alphanumeric LEDs are made up of 16 LED segments that can be individually controlled.

While you could program the segments using appropriate calls to setLed(), it gets tedious to program the right segments and typically you want to display a character. The MeinEnigma software uses a "font", an array defining the 16-bit patterns for each ASCII character. Then it implements a function displayLetter() which accepts an ASCII character and display number and shows the character on the associated LED.

For this example program I have lifted the font and the implementation of displayLetter(). The example program first turns all display segments on and then off using setLedNow() and clearLedNow() to demonstrate controlling the individual segments.

Next it displays the characters "ABCD" by calling displayLetter().

Finally, it displays the entire font character set on the LEDs (which, to save memory, is not the entire ASCII character set).

The listing is short enough to show below.

The full code can be found here.

  MeinEnigma Example

  Demonstrates controlling the 4 alphanumeric LEDs on the main board.
  Uses code from the MeinEnigma software.

  Jeff Tranter


// External library for HT16K33 chip.
#include "ht16k33.h"

// LED font table
#include "asciifont-pinout12.h"

HT16K33 HT;

// Display a character on one of the displays. Leftmost display is 0,
// rightmost is 3.
void displayLetter(char letter, uint8_t dispeno) {
  uint8_t led;
  int8_t i;
  uint16_t val;

  led = (dispeno) * 16;
  if (letter > '`')
    letter -= ('a' - 'A');
  val = pgm_read_word(fontTable + letter - ' ');

  // No lookup table needed, all LEDs are at offset 64
  HT.setDisplayRaw(dispeno * 2 + 64 / 8, val & 0xFF);
  HT.setDisplayRaw(dispeno *2 + 64 / 8 + 1, val>>8);

void setup() {
  // Need to initialize the chip in order for displays to
  // work. This also clears all display segments and LEDs.

  // Clear the RAM to make sure we read data but don't send it.
  for (int i = 0; i < sizeof(HT.displayRam); i++)
    HT.displayRam[i] = 0;

void loop() {
  int i;

  // All segments on
  for (i = 64; i <= 127; i++) {

  // All segments off
  for (i = 64; i <= 127; i++) {

  // Display some characters
  displayLetter('A', 0);
  displayLetter('B', 1);
  displayLetter('C', 2);
  displayLetter('D', 3);

  // Display full character set.
  int j = 0;
  for (char c = ' '; c <= '`'; c++) {
    displayLetter(c, j % 4);

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