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### Topic: Resistor on frontend or rearend of hardware (Read 608 times)previous topic - next topic

#### encryptor

##### Nov 20, 2012, 12:15 pm
The resistor is found after a push button switch in a circuit.  The resistor is found before in a led or 8 ohm speaker.  How do I know where the resistor would be placed if I were prototyping?
peace*&^

#### fungus

#1
##### Nov 20, 2012, 12:58 pm

The resistor is found after a push button switch in a circuit.  The resistor is found before in a led or 8 ohm speaker.  How do I know where the resistor would be placed if I were prototyping?

It doesn't really matter. Put it after the LED if you want...it'll light up just the same.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

#### Grumpy_Mike

#2
##### Nov 20, 2012, 04:17 pm
Quote
How do I know where the resistor would be placed if I were prototyping?

It is all part of the design knowing if you need a resistor to limit any current on not.
Basically the switch resistor is a pull up or pull down resistor, these are needed.
The arduino can not supply enough current to drive a low impedance speaker, the current must be kept below 40mA. So an 8 ohm speaker would give you a current of 5 / 8 = 625mA if connected up directly. This will damage your arduino. So the maximum load on a pin would be 5 / 0.04 = 125 Ohms, therefore you need a 125 - 8 = 117 ohm resistor in line with an 8 ohm speaker. That is going to make the volume very low, but that is another problem.

#### Docedison

#3
##### Nov 21, 2012, 12:06 am
Well If the OP made the mistake He'd have to be deaf and blind... No Worries tho... @625 mA that Speaker ain't long for this world.

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

#### fungus

#4
##### Nov 21, 2012, 12:32 am

Well If the OP made the mistake He'd have to be deaf and blind... No Worries tho... @625 mA that Speaker ain't long for this world.

Bob

Yeah, a whole 3 watts...deafening!

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

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