Only for old fashioned 74xx TTL logic, not for newer CD4xxx Cmos logic.For most gates, low is between 0 and ~1V. High is ~3...5V.
Again you are talking about old TTL. Its datasheet says its maximum input current (going positive) is 1.6mA so its input will be +0.6V if the resistor to ground is 0.6V/1.6mA= 375 ohms. If you leave the input disconnected then its 1.6mA of input current will pull it up to a logic high.I use dip switches to turn the inputs high. But if I don't connect the input to (-) rail through a resistor when I turn the input high the gate doesn't work right. If I measure the voltage drop on the resistor I have .6V for low input. Why I can't just leave the low input to 0V (not connected)?
CD4011 is a CMOS IC. Especially here it is not allowed to leave inputs floating.vs CD4011B which can work with floating low input.
Then if I want to build larger projects, what should I do? I learn and follow youtube projects and people there manage to build for instance, a 4 bit full adder, with no input resistors. But I have problems while doing that. ICs even turn from positive logic to negative logic when input is floating. For larger (tutorial) projects how can I avoid using resistors for every input. It costs space. A lot.
You did not give a link so I found a 4 bit adder on You Tube that uses DIP switches and wrongly uses no resistors. You can learn a lot of wrong things on You Tube and on Instructables.Then if I want to build larger projects, what should I do? I learn and follow youtube projects and people there manage to build for instance, a 4 bit full adder, with no input resistors.
I am not talking about the unused inputs. I am talking about the inputs that are manually set to high or low manually, from a dip switch. When the switch is open, the input it's undefined. I am talking about the inputs that at some point will be high.
DIP switches are single pole on and off. If a DIP switch sets a logic low when it is ON then a resistor to the positive supply is supposed to be used to provide a logic high.
The You Tube video shows the array of DIP switches connected to the logic inputs and ground, not the positive supply voltage.
Yes, Digikey has some of the Grayhill 4 position SPDT DIP switches in stock for "only" $3.81US each.
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