Versatile interface framework development
A universal platform for creating devices for the acquisition and processing of biopotentials (EEG, EMG, ECG) is developed. The system is designed to record brain (EEG) or muscle activity (EMG, EKG) and converting the signals into control actions for external devices. Also based on this platform it is possible to create interactive multi-purpose monitors of the state of human health.
The device arranged according to a modular principle and consists of the control communication module and optional remote modules. The control module (CM) based on the STM32F4xxx ARM microcontroller. These microcontrollers allow to vary the computing power and the price of the device without changing the printed circuit board. The CM can operate completely autonomously, powered by its own lithium-ion battery. The CM communicates with the computer via the USB interface with optional galvanic isolation (power and data) module. The CM also acts as a charger (USB) device to the battery. In autonomous mode CM can communicate with the PC, laptop or smartphone via WiFi interface. Also data can be recorded on microSD card.
The interface to the external modules contains: two high-speed serial peripheral interfaces (SPI); digital voltage supply 3.3 V; analog bipolar power-supply ±2.5 V; additional universal input/output ports (UIO). In digital mode the UIO can be used as clock or trigger, in analog mode – like ADC or DAC. It is possible to connect to the CM up to 4 ADC modules with a maximum frequency of digitization.
The overall dimensions of the CM are 6.5 x 5 x 1.5 cm (without shell and battery compartment). The device is supposed under Windows, Linux, Android operating systems; software for MacOS is developed.
At the moment, the converters based on the ADS1298 and ADS1299 are used as remote modules, with the following characteristics:
- ADC resolution 24 bit (provides speed and accuracy of measurements)
- 8 differential or 16 unipolar channels
- sampling rate 16 kHz (ADS1299, 1 kHz per channel) and 32 kHz (ADS1298, 2 kHz per channel),
- the amplitude of input noise 1 µv (ADS1299), 4 µv (ADS1298),
- programmable gain: 1, 2, 4, 6, 8, 12, (and 24 for ADS1299).
Biopotentials digitization options and the available data transfer capabilities provided by the described device allow to use it both in fundamental research and for clinical needs. The possibility of long-term data collection, including recording to the internal storage, give the potentiality of creation on the basis of the platform detailed diagnostics systems for cardiovascular, neurological diseases or abnormalities of the locomotor apparatus. Also highly configurable remote modules give capabilities for the comprehensive analysis of brain electrical activity (EEG) in the laboratory conditions that is required, for example, during brain-computer interfaces developing.