I connected a piezoelectric film to a Arduino Uno board via analog input. However, as I was getting very high voltage values (reaching 5 volts without much movement). Therefore, I added a 1 megaohm load resistor in the circuit to get lower and readable voltage values on the monitor. Now, I am connecting the films in series and thus the voltage should theoretically increase. However, the voltage values on the serial plotter appear less than before with only one film. Do I need to switch the load resistor to a lower to higher value?
I was thinking that since the voltage value theoretically doubles, I should use a 500k load resistor. However, I am not too sure since I don't know the exact reason why we need to add a load resistor in the first place. All I know is that electrical energy generated by the PVDF films is very low, so current must be very, very, very low.