In our most recent project meeting, we focused on determining which tasks were going to be the most difficult so that we could prioritize them. There are two things that we think will test our technical skills the most:
1. Integrating accelerometer data
Since we are not using any kind of absolute position sensors, we will need to calculate position from acceleration by taking a double integral. This is complicated by not having an associated gyro, but we are hoping that we can make certain assumptions (device will start out upright with zero velocity, etc.) since we don't really need to know the exact position in three-dimensional space, just if the height has dropped a certain amount within a certain time. Still, smoothing out what may be noisy data, and figuring out what the time window should be for something to count as a fall, will be an interesting challenge.
2. Generating and Transmitting Audio
Because this device is meant to get help for someone who may be unconscious or otherwise unresponsive, it needs to be able to send a pre-recorded audio message to the cell network. The GSM module we are using will accept a standard analog signal as input, so the Arduino will have to take a digital audio file and convert it to analog. Also, it will need to send commands to the module to connect it with the network.
We expect (and hope!) that the rest of the build will be straightforward with no surprises, but we have budgeted extra time just in case we run into any issues.
Physical Project Layout:
Since we now have most of the components, we tried a number of arrangements to see how they would best fit into a project box. We found that we can put everything into a 16x11 cm box, which will fit nicely onto the small backpack. We are trying to avoid stacking any components on top of each other so that it will be as low-profile as possible, which will hopefully help with durability as well as comfort. Our plan is to design and 3D print a custom box with mounting hardpoints, space for shock-absorbing foam, and a slightly curved upper shell for added strength.