need advice on circuitry question

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bignick270

Joined Mar 25, 2009
36
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.
 

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mik3

Joined Feb 4, 2008
4,843
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.
 

MikeML

Joined Oct 2, 2009
5,444
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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