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For some years now, I have been on a never-ending quest to discover the cheapest way for a miniature vehicle to position itself. One that performs decently that is. My latest idea involved the, less-than-a-dollar, HC-SR04 ultrasonic sensors to acquire a holistic view of the surroundings. But let’s take it from the beginning…

During my summer holidays (and to the dismay of my girlfriend) I was trying to come up with cool projects for the autumn and winter. Then, one day, an idea struck me while eating lunch: A disc-shaped board with many ultrasonic sensors mounted, that would provide a circular view of the surroundings. I googled around for similar projects and did not find something similar, so I decided to move it forward.

In the beginning, I thought the concept was flawed. The way I used the HC-SR04 ultrasonic sensors thus far was by triggering each to transmit an ultrasonic pulse, wait for it to reflect on an object and then determine how far away the object stood by the time it took for the “echo” to return. The problem with this lies in sequentially waiting for each measurement. When there are merely a couple of sensors, it is usually acceptable to wait for every one to finish. Empirically, I know it takes more or less 10 milliseconds for each measurement to complete for ranges under 1.5 meters, common for miniature car applications. Therefore, up to around 80 milliseconds could be wasted for the eight sensors I wanted to have on the board. To make matters worse, the results would be slightly inconsistent as the measurements would not have been initiated at the same moment.”

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