DS1307 SQW Question

Discussion in 'General Electronics Chat' started by tracecom, Sep 23, 2011.

  1. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
    3,871
    1,393
    The following is a quote from one of the DS1307 datasheets.

    SQW/OUT (Square Wave/ Output Driver) - When enabled, the SQWE bit set to 1, the SQW/OUT pin outputs one of four square wave frequencies (1 Hz, 4 kHz, 8 kHz, 32 kHz). The SQW/OUT pin is open drain which requires an external pullup resistor. SQW/OUT will operate with either Vcc or Vbat applied.

    Based on the above, if the DS1307 is running on Vbat power, but SQW is operating with Vcc, and there is an LED connected to SQW, does this LED add to the drain on Vbat? I assume not, but I wanted to know for certain.
     
  2. tgotwalt1158

    Member

    Feb 28, 2011
    111
    18
    Could you sketch it as a diagram please to understand your question well. Even roughly would serve the purpose.
     
  3. tracecom

    Thread Starter AAC Fanatic!

    Apr 16, 2010
    3,871
    1,393
    LED 2 is the subject of my question. Thanks.

    To add some clarity, I can remove the shorting clip from PH2 and thus force the DS1307 to rely on Vbat, but LED 2 is still connected to Vcc and the SQW output is the drain for LED 2, thus LED 2 flashes, but does this cause any additional drain on the battery?
     
    Last edited: Sep 23, 2011
  4. tgotwalt1158

    Member

    Feb 28, 2011
    111
    18
    Hard to understand theoretically but I tell you a simple technique to find out practically. Measure current of both Vbat and Vcc by a suitable meter, note down the values, then remove the LED and measure current of both Vbat and Vcc again. The changed value will tell you which one is responsible of loading LED.
     
Loading...