Purpose: Converting the analog signal acquired from the brain (through the analog circuit) to a digital signal and transmitting it to the computer as digital data. The analog signal from the electrode (filtered and amplified) is the input of the digital system. First, the analog signal (ranging for -6V to 6v) is converted to a digital signal using an the Texas Instruments Analog to digital converter (ADS7813) converter (16-bit accuracy, 256 samples per second), with the microcontroller that controls the timing and transmitting of the signal to the USB to UART Bridge (Silicon Labs) that transmit the signal serially to the PC application.
Our digital circuit design supports up to four analog channels as input, each analog signal will be the input of an A2D converter. In our implementation using PIC16F88 we implemented two channels (Two players game). If we want to implement four channels we can use the PIC16F877A (more I/O). Analog to digital converter (ADS7813) - Converting the signal, we control its sampling rate & reading data by pulses that the microcontroller sends. Microcontroller (Microchip PIC16F88) - We programmed the PIC microcontroller using assembly code. The microcontroller is the most important component of the digital system; it connects between all the components by receiving data on demand from the A2D and sending it to the UART component that send it automatically to the PC. It is very important to control the exact sampling rate/frequency and to check that the system does NOT lose any sample. USB to UART Bridge (Silicon Labs CP210x) - The CP210x is a single-chip USB to UART bridge that converts data traffic between USB and UART formats. We used this bridge to send data to the PC. The PC receives the data as a virtual COM port.
You can see in the schema two channels (on the left) connecting to the microcontroller. RB5 is the output of the microcontroller that connects to the USB to UART Bridge.