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### Topic: Calculating Circuits for Arduino (Read 880 times)previous topic - next topic

#### hippocrypt

##### Sep 30, 2012, 04:13 am
Hello, I have taken some general classes on circuits. I would like to know how to treat the pins on the Arduino. For example I have 6 photoresistors I would like to connect to the 6 analog pins on the Arduino board. Should I treat them as 6 different circuits or 6 resistors in parallel?

#### Grumpy_Mike

#1
##### Sep 30, 2012, 05:16 am
Six diffrent circuits.

#### Docedison

#2
##### Sep 30, 2012, 05:23 am
Also need pull-ups or downs depending on what you wish to accomplish.

Bob
--> 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

#### hippocrypt

#3
##### Sep 30, 2012, 05:30 am
Thanks grumpy.

What is a pull up/down?

#### JoeN

#4
##### Sep 30, 2012, 08:42 amLast Edit: Sep 30, 2012, 08:44 am by JoeN Reason: 1

Thanks grumpy.

What is a pull up/down?

A pull up resistor is a resistor, usually of a high value (anywhere from approximately 1K to 100K with 10K being pretty common but it depends on the situation) between part of the circuit and the high rail, usually 5V for Arduino projects, but it could be 3.3V for the low power systems.  A pull down resistor is the same but to the low rail - 0V.  The point is to pull that part of the circuit to either of the voltages when the circuit goes into the high impedance state of neither voltage being connected.  If that part of the circuit is never in high impedance or the circuit consuming the signal can't misbehave because of high impedance (like an LED) you will never need a pull up or a pull down.

Wikipedia says it even better than I do, and with diagrams:

http://en.wikipedia.org/wiki/Pull-up_resistor
I will never ask you to do anything that I wouldn't do myself.

#### Grumpy_Mike

#5
##### Sep 30, 2012, 10:41 am
Or look how I describe it:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html
For when the pins are inputs.

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