# Coil switching for resonance with an arduino controlled TRIAC

I have a capacitive system which I need to power via resonnance using a coil. Resonance occurs at several frequencies, therefore I need a different coil for each frequency. So far I've manually switched the coil whenever I needed to use the other resonance frequency. However I feel like this process can be automated, so I've designed a shield for my arduino that allows me to do just that, to switch coils using a button or later an automated command coming from the computer to the arduino's serial. (The arduino here is an UNO).

Since it's using alternative current, I needed to use a TRIAC. The design I've come up with so far looks like this

It works this way : The Signal + connector at the top goes into a function generator with an amplifier which outpus an AC voltage which can range from 5V to 20V in higher voltage uses. The Signal - connector at the bottom goes to my capacitive circuit, which itself is connected to a shunt resistor and eventually back to the function generator.

On the shield, as can be seen is a small 2 poles connector onto which the coil is plugged. There's another coil-switcher right next to this one as I'll be using 2 coils on this system but that I haven't shown as it's exactly the same as the first one. There's a small opto-TRIAC (the MOC3031M) to separate the arduino from the rest and to trigger the actual TRIAC. I drive the opto-TRIAC using a simple MOS from the arduino.

My question now is the following : Is that a good way to control such a system?

What I really only want to do is to be able to select between one coil or the other without having to physically change the component.

• I changed the part about the voltage being used, as it was unclear before. It does not oscillate between 5 and 20V. These two values actually indicate some of the possible voltages used in this device. – saeleko Nov 29 '16 at 17:14