Outputs

• Generate step/dir for controlling a stepper motor, or generate PWM/dir for controlling a BLDC motor or standard DC motor
  • For the prototype, the current motor is a stepper.  The end goal is to drive the BLDC motor.
    • Software generates a trigger, then rotates the motor over a configurable period of time
      • For steppers that signal is a series of pulses and a direction signal
      • For BLDC or standard DC motor that signal is a PWM width and direction signal.
    • Once that time has elapsed, return the motor to the start position.  
      • The start position is available as a signal from a hall effect sensor below.  
      • Change the status of the direction pin and generate pulses. The timing is not critical as the bag will expand however fast it needs to, but matching the expansion rate could reduce wear on the bag.
• Drive an SPI or I2C OLED or TFT display.
  • The current settings for the set Rate, Volume, and Pressure should be available at a quick glance.
  • The readings from the patient for those same numbers should be available at a quick glance.
  • Optional: A graph of the history for the patient for measured volume and pressure
• Optional: Write the patient history out to an SD card periodically (when you run out of memory on the device)

Inputs

• Read from four ADC sources for sensors
  • Read from this sensor to determine volume of air being provided  
    • MPXV7002DP Transducer APM2.5 APM2.52 Differential Pressure Sensor
    • This is a closed loop with both ports terminated to an S type pitot tube located in the patient airstream
    • The pressure differential will correspond to the current volume and direction of the air passing by the pitot tube.  This will have to be calibrated for the tube we have designed.
  • Read from this sensor to determine the airway pressure
    • MPXV7002DP Transducer APM2.5 APM2.52 Differential Pressure Sensor
    • The sensor is centered around 2.5v.  This corresponds to no differential.
    • This has one end open to the atmosphere, and one port terminated to the patient airstream
    • If the patient inhales on their own, we need to trigger a cycle.  This will be a negative pressure dip in the signal.  The signal overall could still remain above 0 (2.5v) if the patient is being ventilated with PEEP.  So we need to watch for the dip, not a negative pressure.
    • Once the cycle is initiated, monitor the airway pressure to ensure we do not exceed the target pressure.  If we do, slow rotation of the motor.  This will be an increase in the positive pressure level in the signal.
  • Read from a hall effect sensor to determine when the motor has reached the starting position.
    • There will be a small magnet on the cam.  When the cam is in the starting position, this will align with a hall effect sensor positioned on the top of the base_t model.
    • This could just be attached to a digital pin and use interrupts as well.
  • Read from the BLDC motor field ground connection to determine the current rotation rate and adjust PWM as needed to hit our target rotation rate.  
    • The field ground will produce 9 pulses per revolution, and the gear train is 270:1 ratio.  A cycle is 1/4 turn to full compression, and another 1/4 turn back to start.
    • This could just be attached to a digital pin and use interrupts for the count as well.
• Read from capsense for user buttons.
  • Six capsense buttons will be molded into the top cover.
  • This is to facilitate directly controlling the set Rate, Volume, and Pressure for the minimal interface.
• Optional: Read from SPI to determine user touch locations on the TFT display.  This also requires an interrupt pin.
• Optional: Read an encoder to facilitate menu and history access in some interface.

Logic

• Triggers
  • For set rate ventilation (unresponsive patient)
    • Initiate a compression release cycle at a rate set by the operator
  • For on-demand ventilation (responsive patient)
    • Initiate a compression release cycle when the patient inhales.

• More to come..