Roshan: July 17

The picture of the Parker pump we bought is as follows
As seen here if we connect the tube leading to the arm band to the inlet of the pump then the pump will act as a vacuum and suck out air from the armband.
If we connect the tube to the outlet of the pump then it will act as a pump and pump air into the arm band.
Ideal case would be where we connect to the outlet of the pump and when we reverse the voltage with an H bridge circuit the pump acts as a vacuum and sucks out the voltage from the armband. But as I found out in my research most of these miniature motors come with protection circuits to prevent reverse voltages being applied. Hence if we apply a reverse voltage the correct polarity will be applied to the pump by the protection circuit and the pump would act normally.

The motor from the blood pressure monitor is as follows
As seen here the motor is a normal DC motor that is coupled with some mechanism to make it act like a pump. When the motor rotates the rubber would move up and down and pump air into the arm band. And even when the motor is running in the reverse direction (by applying reversed polarity to the motor) the mechanism would still work similar to the earlier case and pump in air.

Therefore as discussed with Professor and James I decided to include two pumps one to pump in air and the other to pump out air. Therefore the H bridge circuit is no longer needed. The proposed system is as follows
Here the 3 voltages are required from the power supply circuit. All have been provided with DC-DC converters.
5V is for the motors.
3.3V is used for the MCU and the +Vd of the opAmp
-3.3 is used for the -Vd of the opAmp
The MCU would supply 2 PWM signals which are passed through a buffer to drive the mosfets.
The pressure sensor's signal is amplified by the opAmp which is then supplied back to the MCU. The opAmp used in this case is AD620 from Analogue Devices and in this we can directly set the gain by simply connecting a resistor. The datasheet is here

James comments
1. what is the power requirement of the whole circuit when in full operation? can a single battery supply for all 3 different types of supply?
2. what is the model of the microcontroller which provides 2 pwm?

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