Electronic – arduino – DIY electromagnetic shielding (CNC mill)

I guess you're supposed to stick it onto your cellphone, and that's supposed to protect you from nasty E-M radiation.

Electromagnetic radiation can be nasty at some energies, but the EM radiation from your cell phone isn't dangerous. Radiation is dangerous as such when it is ionizing radiation - capable of removing electrons from an atom, creating an ion. Ions are chemically reactive, and it's the reaction that causes harm.

Take a look at this image of the electromagnetic spectrum from Wikipedia:

Your cell phone operates between the radio and microwave frequencies. Ultraviolet light (such as that created by the sun) is the lowest-frequency ionizing radiation.

My initial reaction is that this is total quackery, but let me ask those more knowledgeable in the field: is there any substance to these things?

If you're not convinced by or don't understand the ionizing vs. non-ionizing radiation argument, note that visible light is closer to being a "nasty" ionizing form of radiation than radio waves. Don't worry about it.

leftaroundabout points out that radiation can also be dangerous at high frequencies due to thermal effects. However,

• Low power levels,
• Large thermal mass in your head, and
• High conductivity of any thermal effects by your blood

combine to make this a non-issue.

I'm not entirely surprised that you've got pickup. You've got wires hanging all over the place. I'd suggest two things to do:

1) Twist your phototransistor wires (blue and yellow) together to form a twisted pair. At the same time, make sure your phototransistor connections are as compact as you can without shorting anything - I suggest moving your connection pins much closer together. Also, make your 5k resistor connections using as short a pair of wires as possible - I recommend making the connection on the protoboard right at the Arduino pins without using any wires at all. As a bonus, get some copper braid and enclose your 20 cm pair in the braid, with one end tied to Arduino ground.

2) As close as possible to the Arduino, connect a small (100 pF to 1000 pF) capacitor between D2 and GND. I can't be more specific as to the value, since I don't know what rate the isolator will operate at. Generally, the bigger the better, except that at some point you'll find that the cap reduces signal amplitude as you rotate the motor shaft.