CODEWITHSUNDEEP
c++arduinospi24-bit
Aaru
Aaru

Reputation: 31

Convert 24 bit 2's Compliment (MSB first) value to a voltage

I have an ADC (AD7767) that I am using to measure a differential signal. The data coming from the ADC is a 2's compliment MSB first 24 bit value. I want to convert this value to a voltage. The reference voltage being used is 5 Volts. I'm using the Arduino IDE. What I have so far is basically this:

const long minValue = 0x800000;
const long maxValue = 0x7FFFFF;
signed long result = 0;
....
long voltage = (result * 0x5) / maxValue;
Serial.println(voltage);

This prints a value of 0.

What the values are:

result = 1010101101010101

0x5: aka Vref

(result * 0x5) = 110101100010101001
(result * 0x5) / maxValue = 0

Upvotes: 0

Views: 724

Answers (2)

user207421
user207421

Reputation: 311050

Yu're trying to store a fraction into a long. The result will always be zero. You need to cast one of the operands to double and store the result in a double.

Upvotes: 1

Andrey Derevyanko
Andrey Derevyanko

Reputation: 560

The problem is in long type you're using. It's integer one and as the result is less than 1 you have 0 as result. Using floats you'll have:

(result * 0x5) = 110101100010101001 = 219,305

maxValue = 0x7FFFFF = 8,388,607

Result = 219,305 / 8,388,607 = 0.026 [Volts]

Upvotes: 1

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