Versatile Plus: Device-specific settings

Data acquisition modes

Versatile Plus devices provide several acquisition modes that allow users to balance wireless mobility, acquisition latency, sampling rate requirements and data storage options. Depending on the selected configuration, data can be transmitted via Bluetooth or USB connection:

• USB: the sampling rate is configurable to 256, 512, or 1024 Hz. Data cannot be stored on the internal SD card.
• Bluetooth: the streamed data is sampled at 256 Hz. Data can be optionally stored on the internal SD card at a separately configurable sampling rate (256, 512, 1024, or 2048 Hz), or storage can be disabled entirely.
• These sampling-rate properties apply to EEG, EXG, Photodiode, and DIO signals and are configured via the sampling_rate parameter. IMU is acquired at 32 Hz (not configurable) and, if enabled, stored in the SD card at 128 Hz. See signal types here bbt_device_signal_type_t
• For EEG signals, the Versatile Plus 32 can be configured for 32 channels (two sets of 16-channel sensors) or 16 channels (the first set only). In case you want the Versatile Plus 32 to record using only 16 channels you need to call the bbt_device_new_versatile_plus_16 function

Three concepts are introduced below to explain the differences between USB and Bluetooth:

• sampling rate (SR): how many samples per second the signal is acquired at.
• transfer rate: how often a packet is streamed to the computer (via USB or Bluetooth) or stored in the SD card.
• samples per block: the group of samples carried per packet. samples per block = sampling rate / transfer rate

USB mode

• The amplifier transfers packets to the computer at a fixed frequency of 128 Hz.
• The sequence number is 16 bits and increases by 1 with every new packet.
• It overflows (wraps to 0) every 65536 / 128 = 512 s (8.53 min).

Connection	SR (Hz)	Samples per block	Seq increment
USB	256	2	1
USB	512	4	1
USB	1024	8	1

Bluetooth mode

• The amplifier transfers packets to the computer at a fixed frequency of 32 Hz (streaming), while the packets written on the SD card are saved at 128 Hz.
• The sequence number is 16 bits in both streams, and both count the same 128 Hz clock.
• Therefore:
  • Streamed packets increment 4 by 4 per packet (e.g. 0, 4, 8, ...), always a multiple of 4.
  • Imported SD-card packets increment 1 by 1.
  • Both overflow every 512 s (8.53 min).

Connection	Streaming - SR (Hz)	Streaming - samples per block	Streaming - seq inc	SD card - SR (Hz)	SD card - samples per block	SD card - seq inc
Bluetooth	256	8	4	2048	16	1
Bluetooth	256	8	4	1024	8	1
Bluetooth	256	8	4	512	4	1
Bluetooth	256	8	4	256	2	1

Digital I/O (DIO) port

Versatile Plus EEG devices include a configurable Digital Input/Output (DIO) port that enables event marking and synchronization with other devices. The port can operate either as digital input or as digital output, depending on whether Versatile Plus receives synchronization signals from external equipment or acts as the source of them.

• Digital input: the port receives trigger signals from compatible accessories and external equipment (a button box, a pedal, a TTL cable, etc.). This can be configured setting the signal mode to DIGITAL_INPUT.
• Digital output: the port generates TTL pulses that can be received by the digital input of another device using a TTL cable, to synchronize with other Bitbrain devices or external acquisition systems at sample level. The DOUT sends a pulse every 30 s, each one randomly either short (125 ms) or long (250 ms). This can be configured setting the signal mode to DIGITAL_OUTPUT.

Enabling the DIO port

The DIO port is exposed as a signal of type Digital_Input_Output. Because it is directional, bbt_device_enable_signal is not enough: select the direction with bbt_device_set_signal_mode, passing a value of bbt_device_versatile_plus_dio_mode.

unsigned short count = 0;
const struct bbt_device_signal_t* signals = NULL;
bbt_device_get_signals(device, &count, &signals);
 
for (unsigned short i = 0; i < count; ++i)
{
    if (signals[i].type == Digital_Input_Output)
    {
        bbt_device_set_signal_mode(device, i, DIGITAL_INPUT);
        break;
    }
}
 
bbt_device_start(device);

Use DISABLED (or bbt_device_disable_signal) to turn the port off.

Versatile Plus in Linux

On Linux the device is identified by its MAC address rather than by its name. Retrieve it with bluetoothctl (scan first if the device has not been seen on this machine before):

bluetoothctl scan on              # wait for BBT-VP2-xxxxxx to appear, then Ctrl-C
bluetoothctl devices | grep BBT-VP2-AAA001

Pass that address as the device_name argument:

bbt_device_t* device = bbt_device_new_versatile_plus_32("C4:D3:6A:BE:7C:B1", "Bluetooth", 512);