Update 21.11.2021

After surviving the first 2 weeks after the autumn holidays, we are really pumping away this Sunday. In the meantime, the test equipment for our air sample collection system has arrived.

To test our concept for collecting the air, we ordered an air pump together with switchable valves and a non-return valve, as well as several metres of hose.

The first test was of the pump itself, for which we tied a balloon directly to our air pump.

Here you can see the last moments of our test subject

However, since we want to collect three air samples from different heights, we still have some work to do: First, our probe has to calculate the flight altitude independently in order to then trigger the respective pumping processes. Since we have neither the space nor free weight for three pumps, we connect our tanks via three switchable 2-way valves. One burnt transistor later, we could reliably control the first valve:

Since we always try to uncover all possible sources of error in all construction stages, we conducted some experiments with our first valve. Among other things, we noticed that the switching process fails if one of the two outputs is under pressure, which is why we were able to adjust the configuration accordingly and thus avoid a critical error.

At the same time, we configured our motor driver. We need this so that our motor does not run from start to finish, as the Arduino can neither supply the required voltage nor the necessary current for a motor. By sending simple signals to the driver, it can, among other things, supply the motor with current that can be switched on and off, similar to a transistor.

If you've been following our development blog for a while, you may know that we used a larger development board called the Arduino Uno when programming our sensors, as this is perfect for developing due to the large pins. However, this board would take up too much space in our CanSat, which is why we use a smaller Arduino with a different chip architecture in our probe.

microcontroller size comparison

It may have been a mistake not to start with this architecture straight away, as we have now noticed that a library we used, which is effectively a driver for a sensor, does not work with the new chip. Rewriting the code took a whole morning of work, which could have been avoided.

After all the sensors were working with the new chip, we took a close look at the code that stores all the measurements on our two redundant SD cards, as the entire primary mission depends on it. When we noticed that the saving of files fails if there are already files on the memory cards, we were able to eliminate another source of error.

The programming of our sensors and processes will soon be completed, but we will continue to carry out tests and optimisations to increase reliability.

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