Electronic – Sensing signal on a power line from high side

• The "low" motor speed is instead realized by blocking every negative half cycle of the incoming AC with Diode 1. The "high" speed is realized by bypassing the diode.

• In this particular hair dryer the motor is never in series with the heating elements.

I found your schematic particularly confusing, so I redrew it. In general, try do draw high voltage elements on the top and low voltage ones on the bottom side of the schematic. In this particular case the device is AC powered, so pick an orientation as you wish but stay with it. Signals (not present here) should generally flow from left to right.

^{simulate this circuit – Schematic created using CircuitLab}

Regrettably SW1, SW2, the thermal fuse, the thermal cutout, the electrode and the motor have the wrong schematic symbols:

• SW1 is a three position rocker switch, model SR-71, function type "K". Its three positions are off(open circuit) - fan low(right side only) - fan high(both right and left sides connected to common).

• SW2 is an identical three position rocker switch. Its three positions are cool(open circuit) - warm(right side only) - hot(both connected).

It's called aliasing - if you don't convert the analogue signal to digital at a fast enough rate you get near enough garbage. Consider this picture of a sinewave sampled at too low a rate: -

http://www.iu.edu/~emusic/361/images/digitalaudio-aliasing.png

Imagine the brown waveform is your analogue signal. The arrows are when the Arduino samples the brown signal and the blue dotted line is what you might construe those samples to mean i.e. nothing like the original signal because you are sampling at too slow a rate. You need to "sample" at a rate that is greater than twice the highest frequency of interest such as here: -

However, you should be able to see that the above sampling will miss nuances in the waveform that change too quickly.