IEEE Systems, Man and Cybernetics Magazine - July 2020 - 22

using only dry electrodes. The system was tested and validated under varying conditions. We conclude by showing
representative examples of what the BMI-HMD could be
used for across multiple fields.
BMI-HMD Development
The developed the BMI-HMD comprises three main parts:
1) a portable, wireless biopotential amplifier module to
measure, record, and transmit the physiological signals; 2)
an HMD-based VR/AR system; and 3) dry electrodes for
the sensing of physiological potentials. With the aim of fostering reproducibility, off-the-shelf components were used,
with minimal modifications needed. The following sections present these three parts in more detail.
Biopotential Amplifier Module
To enable practical mobile applications, the biopotential
amplifier module must be suitable for acquiring different
physiological modalities (portable, inexpensive, and light)
as well as have wireless communication capability. Given
these requirements, we selected the OpenBCI Cyton board

(a)

(b)

(c)

(d)

(e)

Figure 1. The biopotential amplifier module and

electrodes: (a) the case for OpenBCI Cyton, battery,
and charger; (b) the case for the daisy board; (c) a
dry flexible electrode; (d) a dry flat electrode; and
(e) a disposable electrode.

Original Straps
Additional Straps

(a)

(b)

Figure 2. The HMD head-strap organization: (a) profile
and (b) top views.
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IEEE SYSTEMS, MAN, & CYBERNETICS MAGAZINE Ju ly 2020

(composed by eight fully differential; independently programmable; and high-gain, low-noise input channels),
along with its optional daisy board, which provides eight
extra input channels [47]. The analog front end in both
boards is the TI ADS1299 analog-to-digital converter for
biopotentials, which is designed for multiple modalities,
such as ECG, EOG, EEG, and EMG. The OpenBCI hardware has been shown to be an acceptable alternative to
traditional research EEG amplifiers [32].
Snap-ended cables [48] were used to support a great
variety of standard electrodes. To power the OpenBCI
boards, we used a 1,000-mA at 3.7-V lithium polymer battery; the capacity of the battery was calculated to last 12 h.
Finally, the OpenBCI boards, the battery, and a USB charger [49] were placed in a custom-designed, 3D-printed case
to host and protect the electronic components.
To keep the modularity aspect of the OpenBCI boards,
the case was divided into two parts. One part encloses the
OpenBCI Cyton board along with the battery and charger
[Figure 1(a)]; thus, it can be used alone if only eight channels are required. In turn, the second part hosts the daisy
board [Figure 1(b)]. The 3D model of the case has been
made available online [50] to facilitate reproduction. Features of the OpenBCI biopotential amplifier include:
◆◆ a single amplifier for multiple physiological modalities:
EEG, ECG, EOG, and EMG
◆◆ wireless communication using the OpenBCI USB dongle
◆◆ configurable to eight or 16 channels
◆◆ an ability to make each channel fully differential (bipolar), or single reference (monopolar)
◆◆ programmable gain for each channel
◆◆ light, at 86 g for the 16-channel configuration and 70 g
for the eight-channel configuration
◆◆ 12 h of operation for 16-channel configuration.
Other amplifiers can also be used [51].
Off-the-Shelf HMD
An Oculus Rift (Development Kit 2) was used with the following specifications: frame rate of 75 Hz and a field of
view (FOV) of 100°. Although the used HMD is not
designed for AR applications, a similar approach to the
one presented here can be performed in other HMDs, such
as the HTC Vive. The original head straps of the HMD are
ideal spots to place dry flexible electrodes, as they cover
relevant brain regions over the scalp (e.g., central, parietal,
temporal, and occipital). Additional textile straps were
also added to allow for more brain regions to be monitored, such as in the case of cybersickness measurement.
Figure 2 illustrates the original and additional strap positions. The HMD straps also serve as support to place the
biopotential amplifier.
Dry Electrodes
The selection of the dry electrodes was based on three
criteria: signal quality, practicality, and comfort [33].
Three different types of electrodes were used-flexible,
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