slawa92:
Hi, Im having troubles with 24V AC valve as well, I figured out the way to get 10V DC signal, but the problem is that when I connect the valve (-) to arduino GND (the walve is powered by 24V AC) the current of the 24V AC transformer hits the skies, any suggestions ?
the 24VAC cannot be grounded anywhere else
your Arduino has to get power from the 24VAC and that too, cannot be grounded anywhere else, make sure you do not connect the USB at any point while in circuit.
[ EDIT : or tie one leg of the 24VAC to ground as it is floating from the transformer secondary. As it is, it could be anywhere between ground and your mains voltage. ]
there are voltage rectifiers that can take the 34 volts DC and convert to your 5V to drive your unit. a simple LM2596 switching voltage regulator will not get hot from the larger voltage drop.
you might be able to get an linear opto to allow you to use a common DC circuit without having to tie into the AC side.
Europe HVAC controls are 24VAC 3 wire with DC controls as you mention. Belimo has quite a few offerings for actuators as you describe.