The answers to this question about CFLs (compact fluorescent lights) in an electronics lab indicate there is some concern about the presence of electronic ballasts and CFLs in connection to radio and audio electronics. It is my understanding that CFLs have a compact electronic ballast in their base. There is the implication that these answers have to do with the switched on steady state noise.
My question is different because I am interested in the possible effect on 3.3 volt digital wires in a prototype circult during the transition of the CFL from off to on and back to off. These CFLs are on 120 volts AC, 60 Hz and they get switched on and off by randomly behaving people. CFLs are at a distance of 3 meters or more from the prototype circuit. The prototype circuit is powered from a cellphone charger and a USB interface. Sometimes a computer is used instead of the cellphone charger.
I am indirectly observing (because I have no oscilloscope) some unexplained rising edges on Arduino inputs where the processor is programmed to pull up with an internal 20K to 50K ohm resistor. The specification states there is a wide range on the value of the resistor. Digital 1 is 3.3 volts. The problem is intermittent and may occur 1 or 2 times within the space of 20 hours. As a prototype the input pins are connected to breadboard jumpers that are 15 cm long and approximately 24 AWG copper. That gauge is 0.511 mm in diameter. The other end of the jumper is a rotary encoder. In the testing period there is no input activity on the encoder so the firmware can be considered to be in a steady state. A rising edge suggests that noise is enough to drive an input down to digital 0 and the subsequent pull-up brings it back to digital 1.
As a prototype the wires are longer than they will eventually need to be. As a prototype there was no electronics enclosure. I am currently running a long term (24 hour) test with the prototype circuit in an aluminum enclosure. Are CFLs in an electronics lab a known cause of flipped digital signals in a 3.3 volt circuit?
Low is defined as
0.2Vcc-0.1V which I interpret to mean 20% of 3.3 volts minus 0.1 volts, in other words, 0.56 volts.