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Author Topic: Olimex EKG shield. Help! Calculating actual ECG voltage from ADC_Value?  (Read 2304 times)

brianzkee

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Help, how can I calculate the actual ECG voltage from the ADC_Value?
Because the ADC_value is int, a 10-bit value (1024) and a reference voltage of 5V. If for example I get a value of 700 converting this to voltage will be like... 700/1024*5V = 3.41V? Well, this is invalid for ECG because it's actual voltage is in millivolts range. Maybe I'm just missing something that's why I'm confused. I think the calculation has something to do with the GAIN. Any Ideas?

Badreddinez

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You need to notice that there is an offset when no electrodes are connected.
Guru will show 300 (ADC Value) which corresponds to the zero voltage.

Thus, the value 400 in voltages is found as follows

Measured_ADC_Value = 400;
Offset = 300;
Resolution = 5/1024;
VoltageValue = (Measured_ADC_Value-Offset)*Resolution;

400 === (Equiv.) === 0,48828125 Volts

Visually, on Guru: the ECG is always between 200-600Max.

Let me know if this satisfies you inquiry.