When I leave my keyboard at rest, it goes to sleep and draws 3.5uA, then after a while(can be over an hour) it suddenly draws 500uA - what causes this. Normal operation is proven as key pressed, wakes up tiny828, transmit keycode then go to sleep(3.5uA). A key press is the normal wake up due to pin-change interrupt on 1 of 7 column sense lines of the key matrix. When the tiny has entered this excess(500uA) state I am able to press a key and bring it back to the normal(sleep) state drawing 3.5uA.
Also discovered that when I attempt to measure supply voltage with a DVM it seems to force the tiny into this excess current state.
I have left the design powered up overnight, after adding extra capacitance on the tiny's 3V supply.
Anyone had any problems like this with a low power uC design?