# 7. Deflation of the Cuff

A project log for Digital Blood Pressure Monitor

Application For Detecting Blood Pressure Using Korotkoff Sounds

• Continuing with the narration from the previous section. The cuff starts to deflate from 170 mmHg.
• Remember that the solenoid valve is closed, so now the air leak is in the air release valve. Here, the recommendation is that the deflation process of the cuff is between 17 and 21 seconds. So we must calibrate this air release valve with a flat screwdriver, so if we turn it clockwise then the valve closes, and counterclockwise the valve opens.

Calibration the air release valve

• The next step is to measure blood pressure values between 70 mmHg and 170 mmHg and save them in the "PressureArray" matrix every 200 ms approximately.
• I have programmed a maximum value of 210 mmHg in the while function in case, during the inflation of the cuff, it exceeds the limit of 170 mmHg, for example 180 mmHg.
• The values stored in the "PressureArray" matrix and per test are between 120 and 130.

Flowchart

```while Pressure_total > 70 and Pressure_total <= 210 loop
Start_Conversion (Converter);
Poll_For_Status (Converter, Regular_Channel_Conversion_Complete, Successful);
Raw := UInt32 (Conversion_Value (Converter));
Volts := UInt32  ((Float (Raw) / 4096.0) * 3000.0);   -- 4096 ADC = 3000 mV
Pressure := UInt32 ((Float (Volts) / 3000.0) * 255.0);   -- 3000 mV = 255 mmHg
Pressure_total := UInt32 (float (Pressure) - 8.0);   -- 3000 mV = 255 mmHg
Print (0, 0, Pressure_total, " mmHg"); -- print blood pressure

PressureArray(X_Pos) := Integer (Pressure_total);
X_Pos := X_Pos + 1;
delay until Clock + Milliseconds (190);
end loop;```

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