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### Topic: PWM as ground...is it possible? (Read 3451 times)previous topic - next topic

#### Voidugu

##### Sep 07, 2012, 10:51 pm
Guys, can i use pwm to connect to ground?
For example, when i set pwm to be 0, can the pwm pin receive current? Can it be used to saturate a PNP BJT by acting as a ground for the transistor's base? If yes, how many mA can it handle as a ground?

Thank you in advance and have a great day

#### Far-seeker

#1
##### Sep 07, 2012, 11:13 pm

Guys, can i use pwm to connect to ground?
For example, when i set pwm to be 0, can the pwm pin receive current? Can it be used to saturate a PNP BJT by acting as a ground for the transistor's base? If yes, how many mA can it handle as a ground?

First, the maximum current (flowing in either direction) that any Arduino pin (including a PWM pin) configured as an output can withstand without potentially damaging pin's internal circuitry is 40 mA, and it generally a good idea to keep the current 10 mA to 20 mA below that if you can.  So put a resistor of at least 220 ? between the pin you are going to use and the transistor.

Second, to make any I/O pin low (i.e. have the same voltage as the Arduino's ground) you just set the pin to be an output with pinMode() and use the digitalWrite() function.

#### Docedison

#2
##### Sep 08, 2012, 02:46 am
Third, the voltage cannot exceed Vcc for the Arduino... Even with a 220 ohm resistor. Dire things will happen.

Doc
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
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#### Voidugu

#3
##### Sep 08, 2012, 07:13 am
Thanks for the answer and the info but you haven't really answered my question.

What i am basically asking is this:

http://arduino.cc/en/Reference/Constants
"When a pin is configured to OUTPUT with pinMode, and set to LOW with digitalWrite, the pin is at 0 volts. In this state it can sink current, e.g. light an LED that is connected through a series resistor to, +5 volts, or to another pin configured as an output, and set to HIGH. "

Can i achieve the exact same thing by setting a pwm pin to 0? In other words, if a pwm pin is set to 0 then can it sink current?

Again thanks :>

#### Docedison

#4
##### Sep 08, 2012, 07:46 am
Farseeker answered your question, so did I neither of us said it was impossible. We did state the conditions. The pin can either source or sink 40 mA. At 50% duty cycle or 1/2 "Voltage out... the pin will sink as much current as it will source.

Doc
--> WA7EMS <--
"The solution of every problem is another problem." -Johann Wolfgang von Goethe
I do answer technical questions PM'd to me with whatever is in my clipboard

#### Voidugu

#5
##### Sep 08, 2012, 08:19 am
Thanks a lot guys Have a nice day

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