Project Report : localization system
Dear Mission Support,
Through this e-mail we will explain what we did and are going to do for the localization project.
The first aim of our project was to use triangulation to be able to locate one chip using three others. To idea was to get the strength of the signal received by the three fixed chips and convert it into distance. We already saw in Belgium that the RSSI (received signal strength indicator) wasn't accurate, but we thought it was mainly due to the interferences and the reflexions because we live in the city.
But, when we took the first measurements to calibrate our chips and find a relation between the RSSI and the distance, we were pretty surprized : even on a wide open area with very few interferences like the Martian desert, the RSSI kept a significant part of randomness. We were able to find a logarithmic function for distance -> RSSI that fits the measurements we got, but the errors between the estimation and the reality were pretty huge : for small distances, the RSSI changes a lot even if both chips don't move, and for greater distances, the small error in RSSI becomes exponential for the distance and we could have an error of 20 m! We knew it wasn't going to be very accurate, but this was way worse than what we thought.
Among the several electronic component we brought, there are some LEDs and a little speaker. We first made a danger alarm : if the alarm chip (a chip connected to a speaker and a LED) gets a signal from another chip, it starts emmiting an alarm sound and the light turns on. The alarm chip starts to get a signal when it is close to the other chip, which would be about 100 m on a wild field or 50 m if there are rocks or hills between them. The danger beacon would be placed next to dangerous spots like cliffs and the alarm chip are supposed to warn the astronauts who are riding an ATV so that they can pay more attention or simply turn around. We tried it yesterday with the ATVs to see if you can be warned on time and it worked pretty well.
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Then we build what we called a "mobile traffic signal" : with three LEDs (green, yellow, red) connected to one chip, we could command them wirelessly. We thought of several applications but none of them was really helpfull. We improved this by switching on the different LEDs depending on the RSSI. Then, we added the speaker wich plays different tones depending on the RSSI also. So, even if the signal strength isn't accurate, it doesn't matter for this use: when you get closer to an emmiting chip, the leds change (from none to green to yellow to red) and the speaker plays a higher tone. It could have two major uses : we can put one in an interesting/dangerous spot and you know when you are close to it. The other use is that each crew member should carry an emmiting chip. If one of them is in danger and can't tell the other members of the crew where he is (becaused he passed out for instance), the other members can find him very easily. We tried it today and it worked well, but sometimes it is really hard to hear the speaker through the EVA helmet. We are gonna improve our code because there are still some bugs and we would like to make a "beep beep" which becomes shorter when you get closer.
We called our last chip (the one with the three leds and the speaker) the "localization chip".
Thank ou for your attention and if you have any question about our projects feel free to ask,
The localization team,
Nicolas and Adrien