Hello, i am using 16 qre1113 sensors in a line follower robot, and i would like to know if i need to put a pulldown resistor in every sensor before the multiplexer Cd74hc or if i can put only one in the reading pin.
The answer is yes you do. Without one the non addressed inputs to the multiplexer float, and cross talk between channels is increased. So I always include them.
Other have not done this, some have run into problems and some report no trouble. But then not everyone has an oscilloscope to check these things.
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