Measuring air volumes accurately

Was designing some tetrahedral balloon envelopes. Even though finding the volume of a perfect tetrahedron is simple i not straight forward to find the inflated volume. Even the smart engineers of places like NASA disagree about the relationship between inflated volume and side length. At the end of the day most people end up determining the volume experimentally and for this you need to

be able to dispense an exact amount of air.

I tried several approaches including making a large piston with a electronic flow sensor:

By integrating the amount of air going ind and out of the cylinder one should be able to determine the volume. Unfortunately it turned out that leakage and uncertainties in the measurement makes this method very inaccurate.

I instead ended up using a pressure sensor and known volume to calculate the volume:

The tank is a disposable low pressure helium tank with a specified volume:

The pressure sensor is a analog sensor with build in signal processing. These sensors are for oil pressure in cars and cheaply available on ebay:

The pressure is simply:

volume = tank_volume * tank_pressure

 

A display box contains a IIC LCD display, tara button and Arduino UNO board. The display displays both absolute and relative volume. When the button is pressed the relative volume is reset to zero.

Arduino sketch for display

 

 

 

 

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