Editing Basic Circuit Building Blocks

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Use this circuit when you want to feed a user input to a digital circuit, for example a PIC input pin.
 
Use this circuit when you want to feed a user input to a digital circuit, for example a PIC input pin.
  
A pull up is a fairly high value resistor (say 1 to 100 K ohms) that is connected to the positive side of the power supply.  This makes the other end of the resistor the same voltage as the power supply (as long as it is connected to a high impedance).  The other end of the resistor is connected to a switch that is then connected to ground.  When the switch is connected current flow through the resistor drops the entire power supply voltage and the input voltage for the circuit is now 0 (sometimes called active low, since when the switch is active the output is low).  Note that a pull up ( just the resistor to V+ ) might be considered a basic circuit by itself.  Pull up is sometimes used without the switch to keep a signal high all the time.  It can also be connected to any other circuit or component that has ( sometimes ) a much lower impedance than the pull up and can thus force the voltage low.
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A pull up is a fairly high value resistor (say 1 to 100 K ohms) that is connected to the positive side of the power supply.  This makes the other end of the resistor the same voltage as the power supply (as long as it is connected to a high impedance).  The other end of the resistor is connected to a switch that is then connected to ground.  When the switch is connected current flow through the resistor drops the entire power supply voltage and the input voltage for the circuit is now 0 (sometimes called active low, since when the switch is active the output is low).  Pull up is sometimes used without the switch to keep a signal high all the time.
  
 
Circuit:
 
Circuit:

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