The magnet strikes back

In a previous post we discussed several ideas on how to detect the direction of neighbouring Phyllos relative to a given Phyllo. Our favourite idea in this post was based on a mix of Wifi and IR : the Phyllos would cooperate using Wifi to turn their IR emitters on one at a time to allow the others to detect it using IR detectors.

But this idea raises several problems. The most notable is IR reflections : they could spoof the Phyllos into detecting neighbours in the wrong directions. We thought we would be able to differentiate an IR reflection from a direct emission by comparing the amplitudes, but according to Alexis, we will have too much trouble. Moreover, we have ignored so far the possible interference with the IrDA which is used for communicating between fixed part and rotating part within the same Phyllo, and it might not be that simple to isolate the interior of the hull of a Phyllo from external IR radiation.

However, we still think the basic idea is good : combining a direction-finding method that allows each Phyllo to enable or disable its ability to be detected, with a communication channel that the Phyllos can use to cooperate and make themselves detectable to the others one at a time.

That’s why we thought of other solutions. Our best idea so far is inspired by the idea of ​​magnetic sensors described in the same previous post. We would like to use a very sensitive and precise magnetometer, like MPU9250, LIS3MDL, IIS2MDC or LSM303 (less precise but more convenient to use) on the rotative part of a Phyllo, to detect a powerful electromagnet in a neighbouring Phyllo. First, the Phyllos talk over BLE or radio (protocol under discussion …) to determine who is here and give each other unique identifiers. Then, in an agreed upon order, the Phyllos turn on their electromagnet one at a time. When a Phyllo has its electromagnet turned on, the others can use their magnetic sensors to find in which direction it is.

In other words, the electromagnet will replace the IR emitters of our previous idea, and the magnetometer replaces the IR sensor. 

The trouble is that there will be plenty of other magnetic sources around : the Phyllo’s own engine, the engines of the other Phyllos. One possible solution is to make a profile of the surrounding magnetic fields during one rotation before turning on any electromagnet. Then, when we detect other Phyllos, we’ll filter out these interfering fields.

Alexis will bring the MPU9250 on Tuesday so that we can check the viability of this possibility. We will keep you posted 🙂

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