Is it true that the PCB traces can act like little antennas and cause a floating input to change with radio interference?

 

Of course.

__________________
Uncle $crooge

 

OK, here's my floating gate story. Shortly after the introduction of the CD4000 series by RCA, I was tasked with designing a battery-powered UART. I built a wirewrapped breadboard that had a lot of ICs - probably more than 25. Prior to this, I had been using 7400 series TTL, and unused gates could be left with the inputs floating. I didn't know about the problem with floating CMOS inputs.
When I powered the board up, it drew way too much current. Some of the chips were warm to the touch. I can't remember how I found out about the need to tie the unused inputs high (or low), but I actually tracked down some of the chips with floating inputs by using a non-contacting IR thermometer. It would detect chips that were only a degree or two above ambient.
This was around 1970, so I can't remember why I was using the thermometer. I'm sure I eventually reverted to the schematic to find unused gates.

__________________
Ron

 

Here's mine.

We were adding a 74HC05 modification to a bunch of boards because someone had not wanted to drive a 5V relay with a proper 5V gate. One of the boards was buzzing, and you could turn the buzzing off and on simply by waving your finger above the 74HC05. The chip was driving the relay, and the modifier had missed adding a wire to an input.

 

JIMB EXPLAINED total right but that is not the end is it boys endless story about floating inputs. get a life you are not contributing if you spent time raving on and on. and inpedance is not complex at all it ia a vector or an angle from apparent pure resistance. god give me a break.

 

Who put the burr under your saddle? Is there a rule that we can't have a little fun in General Electronics Chat?
Impedance is, in general, a complex quantity.

__________________
Ron

 

Impedance is almost as complex as your sentence structure!

 

Upon further review, he is just a troll:

http://www.electro-tech-online.com/v...=134673#134673