6v6gt:
If the power bank switches itself off when it considers that there is insufficient load on it, then you can sometimes get away with drawing current sporadically to trick it into remaining on.I got the idea from an Web article somewhere and did some experiments and arrived at the solution of using a 47 Ohm resistor switched for 20mS every 2000mS ( 1% duty cycle) across the output of the power pack I purchased ( a PNY 10400mAh. 10400mAh that is at an undisclosed internal battery voltage).
I actually use a small 555 timer circuit for this with a transistor, but it would also be perfectly possible to use spare Arduino pin, maybe with a transistor or different resistor / timing values to stay in spec of the Arduino.
Thanks in advance for the help. How is it done the switched, coud it be done with a condenser?, if it that the case do you have any circuit implementing that?