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Doing WAM on TAB SumoBot — Parallax Forums

Doing WAM on TAB SumoBot

pbpb Posts: 6
edited 2005-02-21 23:31 in Robotics
Hello all,

I'm working through the exercises in Wha'ts A Microcontroller using my TAB SumoBot. I'm on Chapter 3, Activity 2. The exercise is about reading the input value of a pin. It calls for a 220 ohm resistor connecting a pushbutton to P3 and a 10K ohm resistor connecting the pushbutton to ground (see figure 3-6 on page 76).

Since the value of Vdd is only +3V on the SumoBot, what resistor values should I use ?



  • Russ FergusonRuss Ferguson Posts: 206
    edited 2005-02-21 23:20
    The 220 ohm resistor will be just fine.

    The 220 ohm resistor is there to limit the current through the stamp pin just in case the pin is accidentally set to be an output instead of an input.

    When the stamp pin is set to be an input there will theoreticallly be no current flowing from the pin or through the resistor, And that means it is not really needed at all.
  • Russ FergusonRuss Ferguson Posts: 206
    edited 2005-02-21 23:31
    I forgot to add that if the pin is set to be an "OUTPUT" it will only have 3.8v instead of the usual 5v. Ohms law says that when there is less voltage across a resistance then less current will flow.

    The bottom line is that the 220 ohm resistor will allow less current to flow at 3.8v, which is good for the pin when it is accidentially set to be an "OUTPUT".

    The 220 ohm resistor placed between an "INPUT" pin and the sensor will not effect your results.
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