Complete the following steps to determine the value of the user-provided pull-up resistor:

  1. Place an ammeter in series with the load.
  2. Place a variable resistor between the digital output line and the +5 V supply.
  3. Set P0.0 to high.
  4. Adjust the variable resistor until the ammeter current reads as the intended current. The intended current must be less than 8.5 mA.
  5. Remove the ammeter and variable resistor from your circuit.
  6. Measure the resistance of the variable resistor. The measured resistance is the ideal value of the pull-up resistor.
  7. Select a static resistor value for your pull-up resistor that is greater than or equal to the ideal resistance.
  8. Reconnect the load circuit and the pull-up resistor.