Additional RLD resistor for safety issue
For safety issue, RLD output is connected to the electrode through a protection resistor. Off
the shelf AD8232 modules usually uses a 360 kOhm resistor (fig. 4) in series with the RLD
output since its supply is 3.3V. Even if the AD8232 module is powered by the Arduino at 3.3
V, in the worst-case failure, the battery voltage value should be considered. So, if a 6V battery
is used, to keep the RLD current limit lower than 10 uA, a resistor higher than 600 kOhm is
needed (current = voltage / resistance) like a 680 kOhm resistor. So, the 360 kOhm resistor
needs to be replaced by a 680 kOhm resistor (fig. 4). In case of a 9V battery a resistor of
1MOhm can replace the 360 kOhm resistor. This operation is the only one requiring some
soldering skill since such resistors (SMD) are very small.
Figure 4: RLD output resistor (circled)
An alternative to replacing the RLD resistor on the AD8232 board could be adding in series a
common through hole resistor (e.g. 330 kOhm in case of 6V battery of 680 kOhm in case of a
9V battery) to the SMD 360 kOhm resistor of the AD8232 board (the sum will be 690 kOhm
for 6V battery or 1040 kOhm for 9V battery). An easy way to achieve this is placing such
resistor between the RL pin of the AD8232 board and the RL electrode (fig. 5 shows a possible
easy solution); however, in this case it is not possible to use the AD8232 plug-in connector,
but it is needed to use the electrodes pins.
