HC-SR04 ultrasonic draining my battery - help me?

I use the following:

http://www.rocketscream.com/shop/mini-ultra-8-mhz-arduino-compatible

http://www.rocketscream.com/blog/2011/07/04/lightweight-low-power-arduino-library/

http://www.incrediblediy.com/2013/08/ultrasonic-distance-measurement-using.html

http://www.ebay.com/itm/NRF24L01-PA-LNA-SMA-Antenna-Wireless-Transceiver-communication-module-2-4G-HE-/400603653460?pt=LH_DefaultDomain_0&hash=item5d45d6a554

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 -