robot using logic gates question

[johnyerich]

hi this is johny erich,,,,,,just wandring do you need a pull down resistor to keep the input of a cmos logic gate chip low if the input is coming from the output of a lm399 comparator.

 

[Vizier87]

I think yes. Float sometimes occur in these logic gates, it'll stabilize your circuit too.

 

[upand_at_them]

Johny, you meant an LM393, right?

If you check the datasheet connection diagram you'll see that the output is open-collector. Which means it's either pulled to ground or allowed to float. So, 1) you don't want the chip input to float and 2) how is the input ever going to go high if you have a pull-down on an open-collector output? What you want is a pull-UP.