Just about to order a low voltage buzzer of ebay and one sort sounds the buzzer at 3.3v and another sort sounds the buzzer at a value you set between 2.7v and 3.8v, does anybody know how you change the pre set value on them. Need a couple of these for different things so being able to change the voltage setting to when it buzzes would be great. It does not state in the advert on ebay anywhere.