A webcam to measure thicknesses??

yup - u would need to do some image processing...
the machine parts (in the background) should have a much different color than the wood pieces...
how fast do those pieces pass the sensor? less than 25Hz?

nope
not capacitive but optical...
or is it impossible to look from the side?

what about a webcam (properly affixed with screws or so... connected to some stable USB box... like an OLinuXino...) that looks at the piece from the side?

for the voltage i saw a transformer here, i think...
http://arduino.cc/forum/index.php/topic,93779.0.html
http://openenergymonitor.org/emon/

yay! 

what if u use a variation of "average mean", that uses absolute values?
sum_i=1ⁿ  (a_i)/n
that would almost give u the wanted result...  

EDIT: oops - that would not really help (just 10%)... lol - sorry - i have no idea anymore what could cause that error...

r u sure ur oscilloscope is sufficiently accurate?
although errors of 60% would b funny...  

uhm
why do u take the RMS value (it contains square values)?
http://en.wikipedia.org/wiki/Root_mean_square

i think the arithmetic mean would b the right value...
http://en.wikipedia.org/wiki/Arithmetic_average#Arithmetic_mean

have u seen this:
http://arduino.cc/forum/index.php/topic,125952.0.html  ?

1.
ok - that sounds safe...

2.
i c

3.
ok - then it should work... how many measurements do u take? since it is AC, the voltage changes quite rapidly and strongly, i guess...

1.
how do u get a mainspower plug through that tiny hole?

2.
that sparkfun sensor can b integrated easier, i guess...
one just snaps it on the mains power line...

3.
possibly u just measure the reactive power?
i have no idea how that sensor works, when there r 2 wires with the same current (just the direction is the oposite)...
i think u should wait for the high voltage experts... they should b here within a day...

did u try this:
http://en.wikipedia.org/wiki/Capacitance_multiplier ?

could it b that u pick up a lot of 50Hz noise?

did u try to make a shielding below and around the sensor plate?
some grounded metal foil should suffice...

1.
coils/capacitors have logarithmic/exponential curves...
http://www.falstad.com/circuit/e-induct.html
http://en.wikipedia.org/wiki/Inductor#Inductance_formulae

2.
how do u plan to make the primary side of that sensor?
it seems to b a little bit dangerous for my taste...
do u know an electrician?

Hi Nuno!

R_L seems to be outside of the CST1020 according to the picture...
Let R_L=100, then appr. 100mV on R_L translate to 1A... 200mV to 2A...

I hope u took sufficient care to uphold proper insulation...
How did u do it?

Bye

it seems like it is controlled by temperature...
there is no other way to turn the relays on or off...
the temperatures can b controlled by the potentiometers...

there is a I2C library:
http://www.arduino.cc/en/Reference/Wire

the I2C pins of the arduino nano r: pin 4 and pin 5
http://arduino.cc/en/Main/ArduinoBoardNano

have fun... 

MacGyver rulz...