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Products => Arduino Due => Topic started by: eng_mac on Jun 25, 2013, 04:27 pm

Title: reading 3.9v by ADC Arduino due
Post by: eng_mac on Jun 25, 2013, 04:27 pm
hallo ,
i purchased a new Arduino Due circuit , and i am trying to read analog signal with diffrent levels 0v  1.3v  2.6v  3.9v . but i don't know , if i can make this with arduino due or not , because the maximum voltage rate is 3.3v .how can i do this ?
Thanks
Title: Re: reading 3.9v by ADC Arduino due
Post by: Grumpy_Mike on Jun 25, 2013, 04:47 pm
The only way to read a voltage higher than the supply voltage is to reduce the voltage you want to read with a potential divider and read the lower voltage and then multiply it up by the same amount as the potential divider cuts it down.
Title: Re: reading 3.9v by ADC Arduino due
Post by: eng_mac on Jun 25, 2013, 05:33 pm
thank you for your reply ,i want to know also , what happened internally when i connect a voltage more than 3.3v?
what is the value of ADC result register when i connect 3.9v?
Title: Re: reading 3.9v by ADC Arduino due
Post by: Gericom on Jun 25, 2013, 06:12 pm

thank you for your reply ,i want to know also , what happened internally when i connect a voltage more than 3.3v?
what is the value of ADC result register when i connect 3.9v?

The chip could be damaged, and if it would still work, the value would be 4095 (if you're using 12 bits).
Title: Re: reading 3.9v by ADC Arduino due
Post by: Grumpy_Mike on Jun 25, 2013, 10:41 pm
Quote
what happened internally when i connect a voltage more than 3.3v?

The ESD protection diodes become forward biased and conduct current into the power rail. This can blow the diodes open circuit and stop it working. It can also put too much current into the multiplex circuits and blow that.

As a golden rule you should never apply a voltage to an input pin that exceeds the power supply of the chip.