For the One Hertz Challenge I had to pick between a few of my projects. I’ve always had a soft spot for retro LED displays, especially when they’re reused in modern applications. There’s something special about seeing old-school 7-segment displays glowing again   driven by a Raspberry Pi.

For this contest I decided to go with my TinyNumberHat 9. It’s an expansion board for the Raspberry Pi Zero / Zero 2W that drives nine vintage ALS314 7-segment LED digits through an HT16K33 controller. It also features a Qwiic connector, allowing you to hook up additional I²C boards or  connect the hat to a different host, like an Arduino.

With nine digits available, it can count pretty far, show timestamps, or even display short text messages.

The demo code is simple and written in Python. The board also has four buttons, letting you switch between different display modes:

• Clock

• Date

• Timestamp

• Message
  
  Demo:  

  
  
  A  very simple implementation on python: 

  from smbus import SMBus
  from datetime import datetime
  import time
  
  HT16K33_ADDRESS_0 = 0x70
  HT16K33_CMD_BRIGHTNESS = 0xE0
  HT16K33_ENABLE_DISPLAY = 0x81
  HT16K33_TURN_ON_OSCILLATOR = 0x21
  LED_DRIVER_BRIGHTNESS_LEVEL = 15
  SMBUS = 1
  
  
  class TinynumberHat():
  
      def __init__(self) -> None:
          self.bus = SMBus(SMBUS)
          self.ht16k33_i2c_address = HT16K33_ADDRESS_0
          self.dp = True
          # Turn on oscillator
          self.bus.write_byte(self.ht16k33_i2c_address, HT16K33_TURN_ON_OSCILLATOR)
          # Enable display (no blinking mode)
          self.bus.write_byte(self.ht16k33_i2c_address, HT16K33_ENABLE_DISPLAY)
          # Clear display
          self.bus.write_i2c_block_data(self.ht16k33_i2c_address, 0x00, [0x00] * 16)
          # Set brightness 0-15
          self.bus.write_byte(self.ht16k33_i2c_address, HT16K33_CMD_BRIGHTNESS | LED_DRIVER_BRIGHTNESS_LEVEL)
          # Fill with 1, turn on all segments
          self.bus.write_i2c_block_data(self.ht16k33_i2c_address, 0x00, [0xff] * 16)
          # Clear display
          self.bus.write_i2c_block_data(self.ht16k33_i2c_address, 0x00, [0x00] * 16)
  
          self.numbers = {
              '0': 0b00111111, '1': 0b00000110, '2': 0b01011011, '3': 0b01001111,
              '4': 0b01100110, '5': 0b01101101, '6': 0b01111101, '7': 0b00000111,
              '8': 0b01111111, '9': 0b01101111, '.': 0b10000000, '-': 0b01000000,
              ' ': 0b00000000, 'A': 0b01110111, 'B': 0b01111100, 'C': 0b00111001,
              'D': 0b01011110, 'E': 0b01111001, 'F': 0b01110001, 'G': 0b00111101,
              'H': 0b01110110, 'I': 0b00110000, 'J': 0b00011110, 'K': 0b01011001,
              'L': 0b00111000, 'M': 0b00010101, 'N': 0b01010100, 'O': 0b00111111,
              'P': 0b01110011, 'Q': 0b01100111, 'R': 0b01010000, 'S': 0b01101101,
              'T': 0b01111000, 'U': 0b00111110, 'V': 0b00111110, 'W': 0b00011101,
              'X': 0b01110110, 'Y': 0b01101110, 'Z': 0b01011011
          }
  
          self.numbers_2 = {
              1: 0b00000101,
              2: 0b01110110,
              3: 0b00110111,
              4: 0b00011011,
              5: 0b00111101,
              6: 0b01111101,
              7: 0b00000111,
              8: 0b01111111,
              9: 0b00111111,
              0: 0b01101111
          }
  
      def show_time(self):
          buffer = [0x00 for x in range(0, 16)]
          self.dp = ~self.dp
          time_now = datetime.now().strftime('%H-%M-%S%f')
          buffer[0] = self.numbers.get(time_now[0], 0b01000000)
          buffer[1] = self.numbers.get(time_now[1], 0b01000000)
          buffer[2] = self.numbers.get(time_now[2], 0b01000000)
          buffer[3] = self.numbers.get(time_now[3], 0b01000000)
          buffer[4] = self.numbers.get(time_now[4], 0b01000000)
          buffer[5] = self.numbers.get(time_now[5], 0b01000000)
          buffer[6] = self.numbers.get(time_now[6], 0b01000000)
          buffer[7] = self.numbers.get(time_now[7], 0b01000000) | 0b10000000 if self.dp == True else self.numbers.get(
              time_now[7], 0b01000000)
          buffer[8] = self.numbers.get(time_now[8], 0b01000000)
          self.bus.write_i2c_block_data(self.ht16k33_i2c_address, 0x00, buffer)
  
      def show_string(self, string):
          buffer = [0x00] * 16
          buffer[0] = self.numbers.get(string[0], 0x00)
          buffer[1] = self.numbers.get(string[1], 0x00)
          buffer[2] = self.numbers.get(string[2], 0x00)
          buffer[3] = self.numbers.get(string[3], 0x00)
          buffer[4] = self.numbers.get(string[4], 0x00)
          buffer[5] = self.numbers.get(string[5], 0x00)
          buffer[6] = self.numbers.get(string[6], 0x00)
          buffer[7] = self.numbers.get(string[7], 0x00)
          buffer[8] = self.numbers.get(string[8], 0x00)
          self.bus.write_i2c_block_data(self.ht16k33_i2c_address, 0x00, buffer)
  
      def show_date(self):
          buffer = [0x00] * 16
          d = datetime.now().strftime('%d%m-%Y')
          for i in range(len(d)):
              buffer[i] = self.numbers.get(d[i], 0b01000000)
          buffer[1] = buffer[1] | 0b10000000  # put dot
          self.bus.write_i2c_block_data(self.ht16k33_i2c_address, 0x00, buffer)
  
      def show_timestamp(self):
          buffer = [0x00] * 16
          ts = str(int(time.time()))
          for i in range(min(len(ts), 9)):
              buffer[i] = self.numbers.get(ts[i], 0b01000000)
          self.bus.write_i2c_block_data(self.ht16k33_i2c_address, 0x00, buffer)
  
      def read_key_data(self):
          keys_data = self.bus.read_i2c_block_data(self.ht16k33_i2c_address, 0x40, 5)
          keys = keys_data[4]
          return keys
  
  
  if __name__ == "__main__":
      tiny_number_hat = TinynumberHat()
      text = ' HELLO HACKADAY 1HZ CHALLENGE '
      mode = 16
      while True:
          key_data = tiny_number_hat.read_key_data()
          if key_data != 0:
              mode = key_data
          if mode == 128:
              text = text[1:] + text[:1]
              tiny_number_hat.show_string(text)
          elif mode == 16:
              tiny_number_hat.show_time()
          elif mode == 32:
              tiny_number_hat.show_date()
          elif mode == 64:
              tiny_number_hat.show_timestamp()
          time.sleep(0.1)