Pull up and pull down resistors

Other Hardware General Electronics
1

LarryD,

I too am relatively new to programing the Arduino. I have a question about the pulldown resistor in this circuit. I work on equipment that is ground switched and the low condition is almost always 0.7VDC, never 0 volts. Is the pulldown resistor in this circuit there to reduce the input pin to 0? I built this circuit and measured ~1.9VDC at PWM pin 2 and 3 when the resistor is not in the circuit. I do not understand why the PWM input pin has a voltage, is that a design feature of the Arduino?

Thank you for any insight you may have, Hunter

2

A switch can be wired in one of two different ways.

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  1. The switch can be between the pin and GND with a pull up resistor to 5v.

OR

  1. The switch can be between the pin and 5V with a pull down resistor to GND.

Sounds like you are talking about the first.

When you are talking about a PWM pin, it sounds like you are referring to an output, not an input.

A PWM output pin actually has a rectangular wave on it, it outputs pulses of voltage.

PWM

A voltmeter will measure the average voltage of these pulses.

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For a 5v Arduino, for a logic 0 (LOW), voltages less than 1.5v are LOW,
VIL.

For a 5v Arduino, for a logic 1 (HIGH), voltages greater than 3v are HIGH,
VIH.

1 Like
3

LarryD,

That's a lot of great info! Thanks!!

4

@idontwantapickle,

Topic split from another topic. Please do not add your own questions to the end of other people's topics.

Could you take a few moments to Learn How To Use The Forum

It will help you get the best out of the forum in the future.

Thank you.

5

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