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# Convert Raw value to voltage in an ADC

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(@ranjanpal)
Eminent Member
Joined: 3 years ago
Posts: 15
Topic starter

Hi,

Lets say we have an n-bit ADC whose operating/supply voltage is Vs=3.3volts. It does not have a pga (programmable gain amplifier). So to convert raw value of the ADC into equivalent voltage, we can use the formula:

V_in =  (Raw data from ADC) * (Vs/2^n)                       where, Vs=supply voltage=3.3volts

In another scenario, we have an ADC. with same operating/supply voltage is Vs=3.3volts. It has a pga with different full scale range voltage=V_FSR ( for example  ADS1015, in data sheet Pg 10, Table 3: Reference  https://cdn-shop.adafruit.com/datasheets/ads1015.pdf  ). Here we see. V_FSR is not equal to Vs. In this case, to convert raw value of the ADC into equivalent voltage, will the formula be:

V_in =  (Raw data from ADC) * (Vs/2^n)                      where, Vs=supply voltage=3.3volts

or

V_in =  (Raw data from ADC) * (V_FSR/2^n)

Could you please clarify which formula is the correct one?

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(@hans)
Joined: 11 years ago
Posts: 2641

Hey there 😊

Honestly, I'd take this one:

Posted by: @ranjanpal

V_in =  (Raw data from ADC) * (Vs/2^n)                       where, Vs=supply voltage=3.3volts

As far as I recall, but I most certainly am not an expert on this stuff, ADC's do their work in reference to what powers them (3.3v if that is what you are using to power the ADC).

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