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Pressure Control Software

Description. Software for an airplane cabin pressure control system. The airplane motor constantly pumps air into the cabin and a valve controls the flow of cabin air to the outside. It is desired not to have too much pressure relative to the surrounding air to put less stress on the airplane frame. The software controls the valve depending on user input and measured pressure differences.

Hardware

This Arduino software was developed by Denk Development in Mar 2019 for the microcontroller Atmega 328P.

Wiring

as-is + the following

  • Connect a second Arduino to the motor through a motor shield (shield pins 1 and 2, as well as GND and VCC).
  • Connect the Main-Arduino to the Motor-Arduino by hooking up the digital pins 5 <--> 5, 6 <--> 6, and 7 <--> 7, as well as GND <--> GND.

Software Architecture

The software is split into the following sub-parts:

  • Main program. Controls the program flow and contains the main event loop.
  • Pressure delta. Two things: (1) Reads the analog input from a potentiometer which is set by the user to control the target pressure difference. Its output is a pressure difference in PSI (float). (2) Reads the analog input from a pressure sensor. The values correspond to the difference between cabin pressure and external pressure. Yields values in PSI (float).
  • Display controller. Shows four things on the display: (1) selected target pressure, (2) measured pressure, (3) motor position, (4) target motor position.
  • Valve control. Takes actual and target pressure values and adjusts a valve accordingly.

Upload to the Arduinos

There are two .ino file, one for the Motor-Arduino, one for the Main-Arduino.

  1. Open the file at PressureControlSoftware/MotorController/MotorController.ino and upload it to the Motor-Arduino (the one with the motor shield).
  2. Open the file at PressureControlSoftware/PressureControlSoftware.ino and upload it to the Main-Arduino (the one that is connected to display, potentiometers, ...).

Parameters

Parameters can be adjusted in the header file Parameters.h. Not that instead of using a comma ,, a dot . must be used for decimals. Lines are terminated with a semicolon ;.

  • Tolerated PSI delta toleratedPsiDelta, akzeptierte Differenz von Soll- und Ist-PSI, permitted value range [0, maxPSI]. After which difference in preassure levels (target vs. actual) a motion is being triggered. Note that there is no tolerance for motion because this is already caught by the motor positioning tolerance.
  • Low speed PSI delta lowSpeedPsiDelta, permitted value range [0, maxPSI]. Threshold after which the motor will turn slower.
  • Motor speed motorSpeed, permitted values range (0,1000]. Defines how many milliseconds within one second the motor is permitted to move. When set to 1000, for instance, the motor may more all the time. When set to 200, it will move for (at most) 200 ms and will stay still for the next 800 ms.
  • [disabled] Valve adjustment speed valveSpeed, Geschwindigkeit der Ventilanpassung, permitted value range [0, inf). How quickly the valve adjusts do divergence of actual and target pressure. Per 100 ms.
    Now controlled through the MotorController.ino script or motorSpeed variable.
  • [disabled] Opening tolerance openingTolerance, Motor-Positions-Toleranz, permitted value range [0, 1]. Controls which deviation of target motor position and actual motor position is still tolerated until a motion is being triggered. If the motor target is e.g. 0.2, and the measured position is 0.25, nothing will happen with an openingTolerance greater than or equal to 0.05. The tolerance for motion is derived from this value through division by 2. So while adjusting the motor position, movement will not stop unless half of the openingTolerance is reached.
  • [disabled] Minimum valve opening, minOpening, geringste Öffnung des Ventils, permitted value range [0,1]. Once a deviation from the target PSI is exceeding toleratedPsiDelta the valve will be opened to minOpening the least. May be set to 0 when in doubt.
  • [disabled] Max opening at PSI delta maxOpeningAtPsiDelta, Differenz von Soll- und Ist-PSI, bei der das Ventil komplett offen steht, permitted value range [0,maxPSI). At what PSI difference the valve is openend entirely.

Parameters in MotorController.ino

  • Motor slow speed slowSpeed, values in range [0, 1000]. How many milliseconds of a second the motor is turning in slow speed mode.
  • Motor fast speed fastSpeed, values in range [0, 1000]. How many milliseconds of a second the motor is turning in fast speed mode.
  • Motor speed motorSpeed, values in range [0, 255]. How fast the motor is actually turning during the movement phases; correlates with motor torque.

Warranty

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.