Weird 74HC595 phenomenon.

[Ketturi]

I was building breakout board for 74hc595, because I had only smd versions in stock and I prototype with breadboard. I don't know if this is due to ic or other factors (ghost capacitance, ac coupling/hum), but still mildly interesting: http://youtu.be/PrWEropDdzo (bad audio, I didn't used ext. mic, you may need to turn volume up bit)

And no, it's not Dave style "easter egg"

[SeanB]

Interesting that. It is providing enough power to oscillate and switch the mains voltage induced into the circuit from the breadboard.

I do not think you were very old when FC released Second Reality though...........

[NiHaoMike]

Some multimeters behave in weird manners when trying to measure circuits that have semiconductors and/or capacitors.

[Ketturi]

I do not think you were very old when FC released Second Reality though...........

I wasn't even born actually back then, but hey, nothing wrong with liking things older than liker Aaa'and music in Second Reality is far more better than most music nowdays...

Back to the topic, I too think it is some kind of oscillator circuit, which ac leakage clocks, those semiconductors happens to work chaotically when voltage is just enough to get them change state partially.

[SeanB]

Does it occur with the other outputs?

I remember running that when it came out, needed a special configuration to get enough memory to get it to run reliably without crashing. Then I upgraded to a 486SX.............

[Ketturi]

Does it occur with the other outputs?

Yes it does when trying measure some pins, but seems to be bit random and not follow ICs internal logic, I don't know, maybe it is just that cheap ***** multimeter, but no choices here. Interestingly placement of board and meter also seems to affect when this buzzing and intermittent noise appears. Dunno, maybe test leads are working like antenna and circuit is acting like receiver, and picks up numberstation or something xD

I remember running that when it came out, needed a special configuration to get enough memory to get it to run reliably without crashing. Then I upgraded to a 486SX.............

Memmaker and manually editing autoexec & config to load programs & drivers in correct order to get maximum free memory <3. And last 486 processors were faster than Pentiums. My family have been not wealthiest, so I grew up with these computers, when they were old enough to be free, I just picked them up from friends and neighbors. And sometimes I still use tech from that era, and my passion is old electronics, early transistorized and integrated things. Maybe the stork collided with tardis or flying delorean when I should have born xP 

[amyk]

Might be the ESD protection diodes acting as demodulators. MOS transistors have such high gate impedance that any stray charges around can cause noticeable effects on floating inputs.

[PA0PBZ]

Looks like you are powering the chip from the continuity test voltage, and one of the other pins is picking up the mains via the breadboard. It does not surprise me really.