Alternative GND connection to avoid soldering
Since the Arduino Nano board has only 2 ground (GND) pins, one can connected to the
battery negative terminal and the other one can be connected to both GND pin of AD8232
and GND pin of HC-06. To avoid direct soldering on the boards, it is needed to find a
solution like the one in fig. 9 to use connector cables.
Figure 9: AD8232 GND pin and HC-06 GND pin connections in case of no soldering option
Switch and box
A switch can be placed through the battery cable (positive terminal) to turn on/off the device.
Instead of using an additional LED to check if the device is turned on, it is possible to use the
LED of the HC-06 module (or the other boards) that is ON when the board is powered. Some
holes are needed on the box: one for the switch, one for the electrodes cable and one for the
LED (if wanted, otherwise it can used a LED already available on one of the boards).
Figure 10: an example of device box with 9V battery holder included and a switch
