Nice (although quite distressing for You ;( ) experience, thanks for
sharing. Just curious..: if the board was in a metal box, with a wire
going from circuit ground to the metal box, would (when the box was
closed with a metal lid) the circuit have behaved well even with the
lamp on?

(sure there are possibly still wires going out and acting like antennas,
but given the very low frequences emitted by the lamp, this should not
pose a problem)

PS: now that I think of it, I had a similar experience a couple of months
ago with a dsPIC, discussed here on the list. I have to recover the board
from the trashcan and try it again, but with my desk CFL turned off. :D


At 23.24 2011.12.15, you wrote:
>Here's a nice little time-waster for you all...
>
>You have an opamp circuit breadboarded on the workbench. It's showing=20
>symptoms of oscillation, and the oscilloscope FFT shows a spectral peak=20
>at around 30kHz and ~25dB above the noise floor. There's a second=20
>(smaller) peak at around 9kHz, ~14dB above the noise floor.
>
>After several hours of head-scratching, circuit simulation,=20
>pen-and-paper recalculation and so forth, you decide to give up and take=20
>a breather. You turn the desk lamp off...
>
>And the circuit springs into life, the MCU boots, proclaims that=20
>"powerup diagnostics [have] passed", and proceeds to display perfectly=20
>valid A/D measurements on the serial port. The oscilloscope has also=20
>decided to behave itself -- the peaks are gone, replaced with the=20
>near-DC waveform that's supposed to come out of a well-behaved current=20
>sense amp.
>
>The lamp in question was later found to be emitting a 30kHz peak, plus=20
>harmonics beyond several MHz, and was more than capable of overloading=20
>an RF field sensor at a distance of a foot.. Its effects were still=20
>measurable on the other side of the room.....
>
>Some days, I hate this hobby. Other times, I just hate the offshore=20
>manufacturers who fill the market with garbage which doesn't even meet=20
>EMC regulations.
>
>Errgh.
>
>For anyone interested -- this is a Maplin A29FF "magnifier/desk lamp".
>   http://www.maplin.co.uk/22w-fluorescent-daylight-magnifier-lamp-47980
>
>=A340 for *this*...
>
>--=20
>Phil.
>piclist@philpem.me.uk
>http://www.philpem.me.uk/
>
>--=20
>http://www.piclist.com PIC/SX FAQ & list archive
>View/change your membership options at
>http://mailman.mit.edu/mailman/listinfo/piclist

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.