Electrical Design & Sensors

One crucial component on our CanSat is the Micro controller or the ‘brain’ of the CanSat. We decided to do an initial investigation to determine which was the right one and it was decided we would go for Arduino Pro Mini.

Distance Sensor Analyse

Initially, we wanted to use the infrared distance sensors as our main sensor, as it was smaller and took up less volume, but we found that it had limited range; during our tests we found different issues with this layout as the sensors were affected by external heat sources. We then opted to have all of the sensors being a HC-SR04 ultra-Sound sensor as it can detect a further distance.

This would make sure we obtained a stable flight, but we have had to sacrifice some of space within the CanSat. We have decided to compensate the loss of space by making sure we use a printed PCB board to minimise the space used by wiring. The one issue or risk is we will not be able to integrate the final board, until the electrical components and design is chosen. We will have to then keep to a fixed design and hope no issues arise. Initial prototyping has been started to create a design using software called EasyEDA. This will help us save time in the design phase. An example of the use of the software can be seen below:

Primary Mission Sensor Calibration and Validation

Our primary mission is for the Microcontroller to successfully record pressure and temperature of the surroundings during its descent. The data recorded should be transmitted to the ground station as live feed. We will have the main pressure and temperature sensors on board as it is transmitted to the ground station. Then we will have a secondary sensor on board recording the data as it is collected and transmitted in case of any data loss due to a faulty transmission.

BME280 and GY-21P

We researched components available and decided to initially purchase BME280 and GY 219 Sensors as seen in Figure 7. To record the temperature, pressure and humidity we are using the gy21p sensor because it is more precise than the bme280 sensor. This is because it has two temperature sensors (bmp280 and si7021) and the actual temperature was in between the values recorded by the sensors during a testing and validation process. Whereas the BME280 only had one sensor and the temperature recorded by was sometimes above the actual temperature and sometimes below making it inconsistent. The sensors were tested by placing the sensor in a beaker which was then placed in a water bath with a thermometer and a weather station then covered with cling film. We then raised the temperature of the water bath and recorded humidity from the weather station and the sensor and the temperature from the sensor, the weather station and the thermometer every minute for ten minutes. This was then repeated for the other sensor. An example of the results were for the BME280 was; weather station 22.6 degrees, sensor 25.63 degrees. An example of the results for GY-21P was; weather station: 24.6 degrees, BME280: 25.03 degrees, si7021: 24 degrees.

David and James began by connecting the pressure to a computer that ran a

program designed to record and display the pressure the sensor was detecting. Then Mr Mihalcea placed the connected sensor within a plastic bag to create a closed environment which was connected to a vacuum pump to alter the pressure inside the bag. We used a pressure sensor on a phone inside the bag to record data.

Then, once we had several data points from each sensor, we had to make a decision. Both produced accurate results, but GY-21P seems to fluctuate less from the true value. Since the temperature and pressure data was best on GY-21P for both tests, we decided to go for GY-21P for our final mission choice to collect primary data.