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### Topic: Will the arduino Uno adc burn if the input voltage is around 5.25V? (Read 3084 times)previous topic - next topic

#### yaantey

##### Jan 26, 2012, 03:44 pm
Hey,

I am using 10k resistor in series with 2 schottky diodes which cuts of any voltage above 5.25V? So my question is will this voltage still burn the arduino ADC?

#### be80be

#1
##### Jan 26, 2012, 05:14 pm
The chip is able to use 5.5 Volt supply. The data sheet said 0 to VCC

So if VCC is 5 volts then No i wouldn't use 5.25 on a ADC pin your reading would be off

I would use a 5 volt zener diode

#### Magician

#2
##### Jan 26, 2012, 05:39 pm
All inputs, digital and analog  protected internally with diodes. You need only resistor to limit current < 1mA.     10k is capable to protect up to 15V :   15V - 5V / 10k = 1 mA

#### smeezekitty

#3
##### Jan 27, 2012, 03:11 am
From the datasheet:
Quote
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V

Since the VIN should be around 5v, 5.25 < 5.5v.
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#### cmiyc

#4
##### Jan 28, 2012, 02:59 am
Funny how only pieces of answers are given when the question "Can I put XXX volts on an I/O pin?"

True, the spec sheet says:

From the datasheet:
Quote
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V

So consider your VCC source.  If using Vin, consider how stable your supply is and what it's ACTUAL maximum will be.  When using USB, realize that USB's spec allows Vusb to be between:  4.75V and 5.25V.  Keep in mind there is an on-board fuse (which nominally should be 0ohms, but could drop a small amount of voltage.)

So, if powered by Vusb there is the potential for VCC to drop down to 4.75V which means the Maximum to any I/O pin is now 4.75V+0.5V = 5.25V.

Will it burn the ADC?  No.  If anything did get taken out, it might be that particular input of the MUX going into the ADC.
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

#### be80be

#5
##### Jan 28, 2012, 05:56 am
He doesn't say if he using the pin as a I/O or analog

#### cmiyc

#6
##### Jan 28, 2012, 06:32 am

He doesn't say if he using the pin as a I/O or analog

That doesn't matter.

From the datasheet:
Quote
Voltage on any Pin except RESET
with respect to Ground ................................-0.5V to VCC+0.5V

Notice the words "any Pin"?
Capacitor Expert By Day, Enginerd by night.  ||  Personal Blog: www.baldengineer.com  || Electronics Tutorials for Beginners:  www.addohms.com

#### nickgammon

#7
##### Jan 28, 2012, 07:38 am

I am using 10k resistor in series with 2 schottky diodes which cuts of any voltage above 5.25V?

In what way does a 10K resistor and 2 schottky diodes reduce "any" voltage to 5.25V? I'm just curious, I thought zener diodes were used in that way, but a quick Wikipedia search reveals:

Quote
Schottky diodes' voltage drop at forward biases of around 1 mA is in the range 0.15 V to 0.46 V ... which makes them useful in voltage clamping applications

So presumably it can be done, but how?
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