4070 OR Gate

[FireAce]

Hey fellows, would love some advice on the quad OR gate IC chip. From playing with the EX-OR chip, I found I need to ground the inputs with a 10k res, so the input would fall back to LOW. Now the 4070 OR works a bit different from what I gather, beings, if any or both the inputs is HIGH, the output will be HIGH. Do I need to place a 10K between the inputs and ground?

Reason I'm asking, I dont have any OR gates on my bench, but would love to go ahead and get all the soldering done while I wait for my order to come it. Thanks.

 

[MikeMl]

The only time you need a pull-up or pull-down is if that CMOS logic input would float around; for example if you have a SPST switch connected to it, and with the switch open the input floats, or if that input is unused, e.g. you are using a 2 input nor gate as an inverter. Whether you need a pull-up or pull-down depends on the gate function. For an OR gate, an unused input would be pulled-down (the inactive state of that input).

 

[FireAce]

All the gates will be used, whether "floating input" will be a problem with the OR chip, is what I'm wondering. The inputs will be getting 12v direct, either from a toggle switch, or from another Logic gate.

I'm setting up my own "traffic" lights for my N scale train layout.

 

[MikeMl]

For an OR or NOR, an input that comes from a toggle switch needs a pull-down. For an input driven by another gate, no resistor is needed.

 

[FireAce]

Thanks Mike. I can get some soldering done now!