HC-SR04 ultrasonic draining my battery - help me?

I use the following:





But only need 24 measurements a day - so want to disconnect power to the HC-SR04 in between measurements but have tried with a NPN-transitor without success - so if there is someone who can help, I will be very happy - thank you

I’m guessing you use the NPN transistor between the HC-SR04 ground pin and Ground. It may have found a path to Ground through one of the I/O pins. Set the I/O pins as inputs so they won’t act as Grounds.

Thank you - yes of course I could not see the forest for the trees;-)

Check these pages for more power saving ideas - http://www.gammon.com.au/forum/?id=11497 -