# Will the arduino Uno adc burn if the input voltage is around 5.25V?

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?

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

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

From the datasheet:

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.

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:

smeezekitty: From the datasheet:

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.

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

be80be: He doesn't say if he using the pin as a I/O or analog

That doesn't matter.

smeezekitty: From the datasheet:

Voltage on any Pin except RESET with respect to Ground ................................-0.5V to VCC+0.5V

Notice the words "any Pin"?

yaantey: 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:

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?

A "clamp" configuration. The diode is from the pin to the Vcc. It will connect the uC pin to the +5V bus when the voltage on the input exceeds 5V + the threshold voltage of the diode (0.7V for silicon diodes, 0.15-0.45V for Schottky diodes). Schottky diodes are good for this application also because they are faster than silicon diodes.

Obviously, to not damage the diode (this being internal in the uC or external) you must place a resistor in series with the input, before the clamp diode.