I am having an issue with using a 74150 in a circuit If I set one up on a breadboard as follows: The address lines connected to GND or VCC GND and VCC pins connected Strobe connected to GND Logic probe connected to Output The output goes HIGH with no input If I then connect the relevant input to VCC (as per the address lines) then the output goes low.... Now in my circuit (an arduino with the address lines and output connected to analogue pins but being used as digital) and with the inputs floating normally and then connected to VCC the output never changes. Also when the scope is attached to the floating input the 74150 is making it hover at 0.5v when that input is selected. I created a sketch that runs all 16 addresses and displays the output value.... The address lines change perfectly at 0V and 4.96V so no issues there. I have tried pulling all the address lines low using a 10K resistor network, disconnecting the IC's output and connecting the logic probe to it and also tried replacing the IC with the one from the breadboard.