Note about power supply
The device must be powered only by batteries and the voltage value must be between 6 and 9
V. The minimum voltage supply recommended for the Arduino nano is 7 V however if the
batteries are full charged, the device is able to work fine at 6 V (e.g. 4 x 1.5 V AA batteries full
charged or 5 x 1.2 V AA rechargeable batteries full charged). If operating at 6 V, the acquired
ECG signal may become quite noisy when the batteries becomes to discharge. Using voltage
value higher than 6 V (e.g. a 9 V battery) can avoid this issue.
Other Arduino Boards
The ECG device can work also with different Arduino boards. Arduino Nano and Arduino
UNO were tested. Other boards can be used (such as Arduino Micro, Arduino Mega, ect.)
however the provided Arduino sketch file needs modifications according to the board features.
The ECG device can work also with the HC-05 module instead of HC-06 one.
Hardware specifications
Through the electrodes, the ECG signal is amplified by the AD8232 modules.
AD8232 modules available on the market usually have a configuration of resistors and
capacitors that give a frequency band between 0.5 and 40 Hz. If the frequency bandwidth is
not specified in the documentation supplied by the vendor, it can be check by the component
values (they are usually present in the schematics supplied by the vendor) and the information
taken from the AD8232 component datasheet (available on the manufacturer Analod Device
website) where the calculation of the -3 dB cut off frequencies (for both low and high pass
filtering) are reported.
AD8232 modules usually have a overall gain of 1100 (100 for the instrumentation amplifier
and 11 for a second amplifying stage). Such Gain value can be specified in the variable “Gain”
inside the “Setting” page of the app (see “User Manual” file) to have the right ECG amplitude
value in mV.
Please refer to the AD8232 datasheet for further information (e.g. CMRR, RLD, noise
reduction, etc.).
After amplified and filtered by the AD8232 stage, the ECG signal (still analog signal) is
digitalized by the Arduino board (A0 input channel @ 600 Hz and 10 bits resolution) and then
transmitted to the HC-06 module by the serial communication pins; finally the data are sent to
the smartphone by Bluetooth.
