# Assessing Drivers' Physiological Responses Using Consumer Grade Devices
## 2 Materials and Methods
### Bittium Faros 360  
Faros by Bittium is a small electrocardiogram (ECG) measurement device. It comes in three versions:  
* Faros 90, which offers simple 1-channel ECG measurements,  
Figure 1: Empatica E4 with positions of its sensors.  
* Faros 180, which offers 1-channel ECG measurements and is able to stream data via Bluetooth, and
* Faros 360, which enables 3-channels ECG measurements and is able to stream data via Bluetooth.  
Each version can be mounted to the participant's body in three ways: Fast-Fix, using a cable set, or using a stingray adapter. Fast-Fix, which is a Bittium's proprietary electrode, is designed for quick mounting and is considered as the simplest and most convenient way of using the device. Faros can be mounted also by using cable sets (see Figure 2 left) with up to five electrodes for 3-channel measurements (or three electrodes for 1-channel). This version is considered as the most accurate and reliable version of Faros for measuring ECG because it enables best skin contact during the measurement process. The third mounting option does not require placing any electrodes on the participant's body. It instead uses an elastic textile belt with two electrodes and a mounting pad for Faros (see Figure 2 right).  
The most important feature of Faros is its ECG sensor. The sampling frequency of the provided raw ECG data can be \(f_{s1}=125\) Hz,\(f_{s2}=250\) Hz,\(f_{s3}=500\) Hz, or \(f_{s4}=1000\) Hz depending on the user's needs. From the ECG signal, Faros automatically detects independent heart beats as points R in a PQRST model of the ECG signal, where P, Q, R, S, and T represent specific waves in the signal as presented in Figure 3. It also derives heart rate variability (HRV), sometimes also referred to as R-R or N-N interval, from the time intervals between the consecutive R points, and presents it as a single output in addition to raw ECG.  
Faros is equipped also with a temperature sensor. According to the manufacturer's specifications [75], its characteristic is linear only between 35 and 45 degrees Celsius when the sampling frequency is \(f_{s}=5\) Hz.  
Faros features also an accelerometer with two possible sampling frequencies: \(f_{s1}=25\) Hz and \(f_{s2}=100\) Hz. Its dynamic range can be set to \(\pm 2\) g, \(\pm 4\) g or \(\pm 16\) g.  
Faros 360 can operate in one of two modes: _Datalogger mode_ and _online mode_. To use the datalogger mode, Faros has to be connected to a computer, and the appropriate measurement settings have to be set using the Faros Manager software [71]. Raw data is stored on Faros' internal storage in a European data format (EDF) file. It can be viewed using the provided EDF viewer or can easily be converted to acceleration (ASC) or heart rate variability (SDF) file format. In online mode, Faros periodically (five times in a second) sends data via Bluetooth. After Faros is paired with a computer (or another Bluetooth device), the computer sees Faros as an external serial device accessible over the serial communication (COM) port. The protocol itself and data packet specifications are provided in Bittium's document 810378 [75].  
Figure 2: Faros 360 with cable set for measuring with electrodes (**left**) and Faros 360 with textile belt for electrode-free measurements (**right**).