Text by Victoria Gray
Technicality (Part 2)
Correspondences
Question: V and O to A
How does the sensor sample and transmit data? Can you give us further information about the SDK (Software Development Kit)? Will this be compatible with OSX not just iOS?
Answer: A to V and O
The sensor communicates with the iPhone using integrated Bluetooth Low Energy (BLE). Nothing extra is needed, just a sensor and an iPhone. The SDK is for interfacing with our sensor via iOS (iPhone OS is a mobile operating system developed and distributed by Apple Inc). With some modifications, it can be adapted for OSX (Operating system that powers mac computers). This would necessitate having an iPod Touch / iPad / iPad mini / iPhone running software that would then just broadcast the filtered, processed data to a nearby computer via WiFi.
A sample iPhone app code will be released to you that is easy to use and iterate on, and also a sample code that will allow you to interface with the live sensor data on OSX. In short, the SDK will bundle a lot of pre-configured filters and algorithms so you can basically pull out a string of numbers from 1 – 100 (approximately) that reflect muscle tension.
2000 samples per second per sensor is the maximum transmission rate. Data can be sampled at higher rates (at least 20khz, perhaps). Realistically, for muscle activity, we need the 2ksps transmission only for the frequency filters we are going to be putting on the raw data, computer-side. To do a band-pass filter on 2khz data rate, we are limited to 1000 Hz (Nyquist) which is the upper limit of the frequency spectrum of sEMG signals. We could get away with less. A majority of the frequency content of interest for us, since this is not research, is probably below 500 Hz. So we only go 2x on Nyquist we could reduce transmission to 1ksps and still be able to do our band-pass filters.
