Zero Cross Detector Needed?

Hello everyone and thank you for any help provided.

I'm finishing up my first Arduino project and need some guidance on the final circuit. FYI, I'm not an electrician, but I'm perfectly comfortable working on basic circuits like the one I'm planning. I just want to treat my little Ardunio board right.

So I'm building a coffee roaster using the pid library and some AdaFruit thermocouple breakout boards. I have an lcd interface where I can set the temperature, start a timer, and see some temperatures and other calculations.

My goal is to have a project box with some outlets where I can plug my roaster components into, then plug the box into a wall outlet to power the roaster and Arduino.

I was planning on using a 120v to 5v converter to power the Ardunio, then I saw this:

They're powering the Ardunio with a ZCD. I've read about ZCDs, and I get the theory, but not really the application. Is it just to avoid interference in digital applications?

Then I confused myself more regarding the relay that will drive the heating element. I've used SSRs with premade Auber pids before, but never realized they had ZCDs in them.


My question is, what applications do you need a ZCD? Also, how do people usually power their Arduinos if they're not using a USB or the power supply?


The zero crossing detector just creates a pulse from a AC wave form, it has nothing to do with converting power for an Arduino to use. I can't explain why the person that drew that circuit has a ZCD, it's not like you need to sync a coffee maker to the frequency of the power grid.

I would recommend just using a standard 120VAC to 5VDC USB adapter as they're a cheap and reliable way to get power to your Arduino. As long you give the Arduino a constant 5VDC it really doesn't matter where it comes from.

Zero crossing detection indicates either packet switching of entire AC half-waves, or phase controlled switching. The abrupt increase of current in phase controlled or unsynchronized AC switching results in a broad spectre of harmonic waves, certainly an unwanted effect. When only switching on at zero voltage, and off at zero current, no harmonics are generated. When thyristors or triacs are used to switch AC (in SSR...), it's sufficient to turn these components on at zero voltage; the components then stay on until the current drops to zero.

Nowadays power supplies are switching at a high frequency, not related to the mains frequency. These high frequencies can be suppressed quite well, but this is not always done sufficiently in (cheap, uncertified) wall warts.