The figure below presents a block diagram of the WMD solution. Two EMG pads are associated with each Transmitter/Ground Electrode Module (TGE), which is responsible for providing ground and power to each system component, sampling the muscle activity data from the pads and transmitting the acquired data to the Receiver Station (RS). The RS then receives the information, formulates the data word, and passes it to the PC. The software on the PC is then capable of displaying and recording the signals.

The following sections outline the current state of each sub-component in more detail:

• EMG Pad
• TGE Module
• Receiver Station
• PC Software

The EMG pads are used to physically acquire and amplify the biological muscle activity signal. The specific EMG pads used are devices provided by Dr. Ted Milner from Simon Fraser University's Kinesiology department. The EMG Pad receives its power from the TGE and operates on a voltage range of ±10V. The common ground electrode is located on a physical strap that is placed on a location not affected by the muscle activity signal that is being measured by that EMG. The EMG data output is a signal that is tuned by the user to ensure a maximum output at the rails of operation.

Each TGE is responsible for acquiring the signals from two EMG pads, digitizing these signals, and sending the data wirelessly to the Receiver Station. It also provides the power and ground reference to the EMG pads.

A microcontroller converts the analog EMG signals to digital with 12 bit resolution and time multiplexes the output for the transmitter to send to the receiver station.

The transmitter modulates a base-band digital signal from the microcontroller onto an RF carrier and sends it to an antenna. The wEMG system must operate in the 902-928 MHz ISM band that is commonly used in hospital settings.

Power for the system is provided by either a 3V lithium battery or 2 AAA rechargeable NIMH batteries. A 10V DC-DC converter steps up the voltage from the batteries to power the EMG pads, and a voltage regulator steps down the voltage to 3.3V for the transmitter.

The ground for the EMG pads is provided by means of copper contacts sewn into the velcro strap.

In the picture below, a completed TGE is shown on the left. Obviously it is quite bulky, but this is due to the large components. A beta prototype of the TGE is shown on the right which is currently under work.

The RS is capable of receiving data from up two TGE modules, formulating the correct data structure and communicating this to the PC via a digital I/O PCI card. The RS multiplexes the incoming data from the TGEs onto a data bus for the PC to read.

Below is a picture of the completed RS for the proof-of-concept device.

WMD's data acquisition currently runs in DOS for the proof-of-concept stage. The PC software serves two major purposes. First, it allows the user to graphically observe the incoming data in real-time. Secondly, the incoming data can be recorded for future analysis.

Real-time graphical observation allows the user to correctly setup the EMG electrodes by ensuring correct pad placement and amplification. In addition, the user is shown the signal strength indicator (via RSSI) from each of the transmitting TGEs. This visual representation of receive signal strength lets the operator decide if the incoming signal strength is enough to ensure data consistency.

After the system has been verified graphically and the user is satisfied with the experimental setup, the data acquisition feature can be used to save muscle activity data. When the user begins data acquisition, the system will record the data from each EMG pad into an individual binary data file. The code has been written in such a way that ensures that no data points are lost and that no data points are saved twice, and is compatible for future analysis in programs such as Matlab.

If you have any questions please contact us at: wireless-medicaldevices@sfu.ca

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