need advice on circuitry question

Discussion in 'The Projects Forum' started by bignick270, Oct 2, 2009.

  1. bignick270

    Thread Starter Active Member

    Mar 25, 2009
    36
    0
    I have a portion of my small battery powered project where I have a small vibrator motor. As you can see in the schematic the input signal from a 3.3V PIC32 goes into the INPUT pin on a analog switch. When this signal is high the switch connects 3.3V to the vibrator motor and when it is low it will connect to ground.

    When the device is booting up or if the battery voltage drops too low and the micro controller is shut down the vibrator motor will activate. This could be a good thing to indicate bad batteries but it is annoying when programming and booting up which in my mind outweighs any benefit from a low battery indicator.

    I was wondering if there was a simple circuitry fix to add in if the micro controller shuts down, maybe a pull down resistor on the vibrate line?

    Also the vibrate control line goes directly to the PIC I/O pin.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    You are right about the pull down resistor. If the analog switch has TTL inputs then it will 'see' a high logic if there is nothing connected to it (microcontroller shuts down or delayed boot). Connect a 1K pull down resistor on the vibrate line.
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Put a 10k-100k pull-up (or pull-down, whichever shuts off the motor) on the Pic pin. Since during boot-up, Pic pins default to inputs, the pin is just floating around until you execute the TRIS and PORT instructions to define the pin as an output...
     
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