I killed a ghost

[olivier.jan]

For months I’ve had very strange phenomenon happening which I couldn’t explain..
It started with an experimental 6502 computer on a breadboard working perfectly well on my desk but nowhere else in the room.
It turned out I had forgotten to connect the RAM and ROM ICs to VCC, with proper connections it worked everywhere, but why did it work in the first place?
Then I teached myself Verilog by coding a PAL composite output, which didn’t work until I mistakenly held my hand 5 cm above the breadboard...
While building my H5 I faced also a lot of unexplained issue (some linked to my soldering skills, ok) which would happens regularly for a few hours, then disappear without me doing any change.
Last week, I had this audio connection on a 600xl motherboard not producing any sound, so I gave up, unsoldered the wire, but when I removed it sound finally came out... from a jack not connected! The wire was 1cm from the jack, but I had sound..moving the wire closer or further would just turn off the sound! :shock:
This week it was problems with a gotek, troubleshooting write failures, just to have it working without any changes a few hours later...
So conclusion, my desk might be haunted... :hide:

But I think I finally found the ghost and killed it:
I was experimenting since last night with an Arduino and a RF433 receiver to decode the signal from my projector’s screen remote without success. There was so much noise in the signal that I couldn’t decode anything. Noise is pretty common on these kind of RF receiver, so I tried to analyze a bit more and used the scope. There was a lot of noise, but actually a very regular one, a very nice square wave at....50hz.
At some point, I forgot to plug the jumper to the RF receiver but the Arduino was still getting signal from just the jumper wire, enough voltage to go high at 50hz.

I started unplugging every device on my desk one by one and measuring each time, and when I reached the last, the 50hz signal finally disappeared.
A very simple Anker 6 USB port charger seems to be leaking radio wave all around the place and is now sitting in a drawer.
I tested my 6502 computer, and it doesn’t work at all when I unplug the ram and rom from VCC, my FPGA video circuit is running smoothly, and I expect to face a bit less issues overall.

Conclusion, be careful about the RF generated by poorly shielded equipments, it can really waste a lot of your time on unexplainable issues...

[exxos]

:hide:

I spent ages trying to find a lot of noise on my early PSU builds.. Was like 400Hz or something.. I did find my led ceiling lights caused all sorts of RF.. Anyway turned out it was the fan which I was using to cool the dummy load resistors with :lol: :roll: :headbang:

[mrbombermillzy]

Even so... that not having connected the ROM/RAM to VCC is some sort of Nikola Tesla induced power type of thing!

Maybe I should order an Anker USB charger and switch it on in the middle of the house to 'wirelessly' power all my devices. :lol:

[exxos]

Some chips get powered up by their IO lines... Normally lower current flowing through it, but odd things can happen... When connecting VCC properly, more current, and on breadboard with bad grounding, you get spikes everywhere which cause it to malfunction.

[olivier.jan]

Even so... that not having connected the ROM/RAM to VCC is some sort of Nikola Tesla induced power type of thing!

Maybe I should order an Anker USB charger and switch it on in the middle of the house to 'wirelessly' power all my devices. :lol:

I guess Exxos is right and the power for the RoM and RAM ICs was coming from the IO pins, but there’s clearly induced power also due to this RF.
Plugging a jumper wire on the breadboard near this things gives me readings of more than 1.4v on the scope...