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[on:]

My question is about protecting the analog input pins on an Arduino Mega from over voltage.  I've seen many topics on this, and the zener diode solutions are typically outlined.  These are good solutions.
http://www.thebox.myzen.co.uk/Tutorial/Protection.html

However, my question is this:
If I am always getting my 5V reference from the Arduino 5V pins, would over voltage protection be of any benefit?  For example, I may wish to generate a 0-5V voltage from a pot, by connecting on leg of the pot to 5V (from the arduino), GND, and have the wiper go to an analog input pin.  In this case, it would seem that input protection on the analog pins would add no benefit.  After all, if the 5V (which came from the  Arduino board itself) surges, the Arduino itself is cooked.

Also, I may want to connect an absolute encoder to an analog input.  Again, the encoder needs to be hooked up to 5V.  And if that 5V comes from the Arduino,  transient suppressing circuitry or over voltage circuitry would seem redundant. 

Are my assumptions sound?

[Reply #1 on:]

My question is about protecting the analog input pins on an Arduino Mega from over voltage.  I've seen many topics on this, and the zener diode solutions are typically outlined.  These are good solutions.
http://www.thebox.myzen.co.uk/Tutorial/Protection.html

However, my question is this:
If I am always getting my 5V reference from the Arduino 5V pins, would over voltage protection be of any benefit?  For example, I may wish to generate a 0-5V voltage from a pot, by connecting on leg of the pot to 5V (from the arduino), GND, and have the wiper go to an analog input pin.  In this case, it would seem that input protection on the analog pins would add no benefit.  After all, if the 5V (which came from the  Arduino board itself) surges, the Arduino itself is cooked.

Yes, in that case no over voltage protection is needed nor makes sense to add it. Over voltage protection is useful for signals coming from external circuitry that you have no control over or are known to be of higher or lower (no negative voltages allowed) then the pins can handle.

Also, I may want to connect an absolute encoder to an analog input.  Again, the encoder needs to be hooked up to 5V.  And if that 5V comes from the Arduino,  transient suppressing circuitry or over voltage circuitry would seem redundant. 

 You will have to provide a link to the specific encoder you are talking about, however that aside most encoders (incremental and absolute types) are digital in nature and do not provide a variable analog output voltage.
Lefty


Are my assumptions sound?

[Reply #2 on:]

>>>>
 You will have to provide a link to the specific encoder you are talking about, however that aside most encoders (incremental and absolute types) are digital in nature and do not provide a variable analog output voltage.
Lefty
<<<<

I've been using this encoder, w an analog voltage out:
http://usdigital.com/products/encoders/absolute/rotary/shaft/MA3

[Reply #3 on:]

>>>>
 You will have to provide a link to the specific encoder you are talking about, however that aside most encoders (incremental and absolute types) are digital in nature and do not provide a variable analog output voltage.
Lefty
<<<<

I've been using this encoder, w an analog voltage out:
http://usdigital.com/products/encoders/absolute/rotary/shaft/MA3

Very interesting, I've never never come across an encoder with an analog output voltage before. But back to your question, if you are be powering the encoder with the Arduino's +5vdc voltage source you have no need to provide for or worry about overvoltage protection for the analog input pin in this situation.

Good luck;

Lefty

[Reply #4 on:]

Thanks for the response!

[Reply #5 on:]

There are several "Encoders that provide analog output the first (simplest) would be a potentiometer with gear or other mechanical coupling and the second would be a Linear "Transformer" which is a transformer with a single winding (Usually) as the driven movable "Source" and two secondary windings so wired that they can extract "Phase" differences between the primary and secondary and  secondary windings and there are others that sense "M" or the coefficient of coupling between two windings one stationary and one movable. There are more but I haven't yet finished my morning coffee...

Bob