Acquire biosignal data with g.MOBIlab+

The Simulink model contains the device driver block g.MOBIlab+ . This block reads the biosignal data with 256 Hz into the model over a serial port of the computer. Thereafter a demultiplexer block is used to split the 2 acquired channels. The standard Simulink Scope block is used to visualize the data online. The To File block is used to store the biosignal data on-line onto the harddisk of the computer. By double-clicking the block, the filename session1.mat can be entered. Therefore, the data are stored in MATLAB format and can easily be processed after recording. The Bandpower is used to calculate on-line the power distribution of the EEG signal. The paradigm block is used to show the current EEG bandpower to the subject.

Please note that the signal analysis, storage and visualization are all done with standard Simulink blocks, which can be accessed by drag-and-drop from the Library Browser . The Bandpower blocks are from the g.RTanalyze blockset. This allows the easy and fast setup of custom analysis models. The g.MOBIlab+ block guarantees that the processing is done in real-time.

The Scope block is used to visualize two EEG channels. The EEG signal has an amplitude of ± 15 µV because it is recorded with a bipolar derivation.

Remote Control of g.MOBIlab+

The g.tec remote control unit allows users to read biosignal data over a network connection (TCP/IP) into Simulink. Simulink is used as front-end and all functions of g.MOBIlab+ can be used. Therefore, the acquisition of biosignals under difficult conditions like in a vacuum chamber or cold-chamber is supported.

Bluetooth transmission and SD card logging

g.MOBIlab+ can also transmit the data over a Bluetooth connection. Therefore, a Bluetooth dongle is inserted into the PC/notebook computer. Then, from multiple g.MOBIlab+ setups, a specific one can be identified based on the serial number, and a connection can be established. The following Simulink model is configured to read in all analog input and digital input channels.

By double-clicking on the g.MOBIlab+ block, the following dialog opens:

Check each channel that should be transmitted from the amplifier g.MOBIlab+. Typically, channels 1 and 2 are used for EEG recordings, channels 3 and 4 are used for DC recordings (respiration, EEG, pulse), channels 5 and 6 for ECG or EMG and channels 7 and 8 for external sensors (GSR, temperature). The 8 digital channels can be used as input (channel 1 - 8) or output channels (channel 4 - 7), or can be disabled. The COM Port identifies the Bluetooth communication channel from the PC/notebook to the g.MOBIlab+. Check the Testmode box to enable a sawtooth signal generation on the g.MOBIlab+.

Start the Simulink model by pressing on Start Simulation . The Scope shows the sawtooth signals with different frequencies on the different analog channels. The digital inputs show rectangular signals with different frequencies.

g.MOBIlab+ can also stream data onto a mini SD card. The SD card is inserted into the water protected battery compartment first.

Check the Enable writing to SD card checkbox into the configuration dialog, enter as filename GMOBILAB and start the acquisition. g.MOBIlab+ is now streaming the data onto the SD card and is sending simultaneously the signals to the PC/notebook for visualization. After checking the signal quality of the biosignals, press the Stop button. A dialog window appears that asks if you want to stop the data acquisition or if you want to disconnect the Bluetooth connection.

Click on Disconnect to keep on streaming the data onto the SD card but to close the signal transmission over Bluetooth. Now the subject can move freely around for 36 hours for home observation, sports activities or other physiological experiments.

When the subject returns from the experiment, startup the Simulink model again and click on Start  again. The Bluetooth connection will be established again and the biosignal data can be visualized.

Finally, stop the acquisition with Stop Simulation in the Simulink model. Now the SD card can be removed from g.MOBIlab+ and inserted into a card reader on the PC to analyze the physiological data. With a 1 GB SD card, about 70 hours of data can be recorded.

High-resolution biosignal acquisition with g.USBamp

The g.USBamp Highspeed Online Processing block provides a graphical interface to the g.USBamp hardware which can be used under Simulink to specify the amplifier properties and to acquire the data.

The g.USBamp block output signal provides the biosignal data. The data format is single (float32) and it is scaled in µV. If all analog input channels (16) and the trigger signal (1) are acquired the line width is 17. Use a Demux block to de-multiplex the channels.

Double click on the g.USBamp block to access the configuration window. The configuration window allows you to specify the sampling frequency of the amplifier and to select the channels that should be acquired. Additionally, the bandpass and Notch filters can be selected for each channel. Bipolar derivations can also be defined. The amplitude, frequency and the offset of the test-signal can also be adjusted.

After performing the configuration, click on the Play button of the Simulink model to start the biosignal acquisition and visualization. The Simulink model is updated in real-time because of the hardware interrupt driven g.USBamp block.

This Simulink Scope shows an acquired ECG signal with a sampling frequency of 1200 Hz.

Impedance measurement and calibration with g.USBamp

The g.USBamp blockset contains also blocks for calibrating the amplifier and to measure the electrode impedance of passive electrodes. Hence, copy the blocks into the Simulink model.

Double-click on the Impedance Check window to measure the electrode impedance of each electrode. The window shows the 16 input channels and the 4 reference electrodes. The electrodes are marked in green, yellow, red and blue colors according to their impedance values.

Double-click on  the Calibration block to adjust the offset and the gain of each channel of the amplifier.