Nixie clock: 3 – RTC and expander

luca 16/03/2012 8

BCD Led clock

The clock’s working is:

  • read the current time from RTC;
  • check if time read is different from time shown by Nixie tubes;
  • if so, send the new time – BCD coded – to the I/O expander and from this to Nixie drivers.

I wrote a sketch with the behavior described above; for testing purposes I’m going to use LEDs instead of Nixie tubes.

WIth RTCLib, it’s very easy to get data from DS1307 IC:

  DateTime now = RTC.now();  
  byte rtc_minute = bin2bcd(now.minute());
  byte rtc_hour = bin2bcd(now.hour());

The BCD conversion is performed by the following function:

byte bin2bcd (uint8_t val) { return val + 6 * (val / 10); }

Hours and minutes, BCD coded, are sent to PCF8575 via I2C bus with the function:

void sendOutputs(byte low, byte high) {
 
  Wire.beginTransmission(PCF8575_ADDRESS);
  Wire.write(~low);
  Wire.write(~high);
  Wire.endTransmission();
}

Before sending, I “invert”  (NOT function, ~) the values because, as you remember, LEDs are connected in sink mode.

BCD value for hours is reverted with the function:

byte revert(byte in) {
 
  byte out = 0;
  for(int i = 0; i < 7; i++) {
    if(in & 1) out = out + 1;
    out = out << 1;     in = in >> 1;
  }
  if(in & 1) out = out + 1;
  return out;
}

only because of LED position on my breadboard.

Here’s a video about this “bcd led clock”… a very geek one even if not very readable ;)

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8 Comments »

  1. pitchoilcan 06/04/2012 at 06:17 - Reply

    I get :error:

    PCF8575_Led_rolling_Demo.cpp: In function ‘void loop()’:
    PCF8575_Led_rolling_Demo.cpp:24:8: error: ‘class TwoWire’ has no member named ‘write’
    PCF8575_Led_rolling_Demo.cpp:25:8: error: ‘class TwoWire’ has no member named ‘write’

    I able to compile by change it for
    Wire.write(low);
    Wire.write(high);
    to

    Wire.send(low);
    Wire.send(high);

    but still now a blink from any of the LED’s. Are you using any resistor? I”ve tryed it using just the pcf8575 anf an arduino board, no RTC module. Is that doable and if so what I’m I doing wring?

  2. pitchoilcan 06/04/2012 at 06:19 - Reply

    I get :error:
    PCF8575_Led_rolling_Demo.cpp: In function ‘void loop()’:
    PCF8575_Led_rolling_Demo.cpp:24:8: error: ‘class TwoWire’ has no member named ‘write’
    PCF8575_Led_rolling_Demo.cpp:25:8: error: ‘class TwoWire’ has no member named ‘write’
    I able to compile by change it for
    Wire.write(low);
    Wire.write(high);
    to
    Wire.send(low);
    Wire.send(high);
    but still now a blink from any of the LED’s. Are you using any resistor? I”ve tryed it using just the pcf8575 anf an arduino board, no RTC module. Is that doable and if so what I’m I doing wrong?

    • luca 10/04/2012 at 08:07 - Reply

      Hi

      You’re probably using an older (< 1.0) version of Arduino IDE… anyway you don’t need a RTC module for this example, could you post your connections so I can check?

  3. pitchoilcan 06/04/2012 at 07:15 - Reply
  4. Fernando Garcia 25/12/2012 at 18:27 - Reply

    Hello!

    I’m trying to build a circuit with a RTC and a PCF8575 .

    It happens that the RTC does not tell the correct time.
    There must be some conflict.

    The code I’m using to test is this:

    #include // Librarie from Henning Karlsen
    #include

    DS1307 rtc(20, 21); // Indica em quais pinos o RTC está conectado.
    static byte tabela1[] = {1,2,4,8,16,32,64,128};
    static byte tabela2[] = {128,64,32,16,8,4,2,1};

    long millis_antes = 0;
    void set(byte b0,byte b1)
    {
    Wire.beginTransmission(0×20);
    Wire.write(b0);
    Wire.write(b1);
    Wire.endTransmission();
    }

    void setup()
    {
    Serial.begin(38400);
    rtc.halt(false); // Inicia o funcionamento do RTC.
    Wire.begin();
    //Todos os pinos OFF
    set(0,0);
    }

    void loop()
    {
    if(millis() – millis_antes > 5000)
    {
    millis_antes = millis();
    Serial.print(“Horario: “);
    Serial.println(rtc.getTimeStr(FORMAT_LONG));
    }

    for(int i = 0; i 0; i–)
    {
    set(tabela1[i],tabela2[i]); // Apenas o pino 1 ON.
    delay(100);
    }
    set(255,255); // Todos os pinos ON
    delay(200);
    }

    The LEDs blink correctly, but the time printed on the serial monitor is:

    Horario: 27:85:85

    I have tested your code and the same thing occurs.

    Any suggestions on what might cause the problem?

    Tank you.

    Fernando Garcia

    Sorry for english.

  5. Fernando Garcia 25/12/2012 at 18:43 - Reply

    The code does not appear correctly.

    Here’s a link to it.

    https://gist.github.com/21dfdc057cfbd1cc44a9/5e7c42002b4025b9d48a21896d81c9a6bd74cbba

    Best regards.

    • luca 11/01/2013 at 08:32 - Reply

      Hi Fernando,

      are you using an Arduino Mega?

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