Arduino AC Power Shield!

Hi All,

After some work I did with triacs and dimming, I have made a AC power shield! It has 4 triac driven outputs, my current prototype can only handle about 1A per channel, but The final version I am hoping for 2.5A or more (300W). It also includes a zero-cross detection circuit to be able to use an interrupt and dim AC devices. I have 2 or 3 prototypes for sale (will work fine for testing and simple use) for $25. Please let me know if you are interested an have the time in the next week to test this and let me know if I should make any changes before I order a first production batch. I am hoping to keep the price around $30.

The only problem I had with the prototype batch is the routing of the pins... I am not sure if I should do a separate female header row (like the prototype shield) or find some long tail female headers to go through.

Please let me know if you are interested in testing one of the prototypes (only charging to recoup some of my cost - I will make sure you get a big discount on the final version!).

Hmmmm, this shield looks more dangerous than the DANGER shield. With such number of electronics newbies out there, you need to add a HUGE disclaimer in the board, and start counting the number of casualties.

Yes this is true! There is a warning, although I may need to increase the text size! All the HV contacts on the bottom are going to be covered… liquid electrical tape, hot glue, something like that… I will try to post some vids of it in action tonight.

I don't think that will be good enough.

Looking at all the traces, there is really no separation between 5V and the possibly fatal 120V part. And there's always the odd user that fiddles with the circuit and forgets to unplug the power. I know because I've done that when I thought I was 'in control' and was lucky a few times.

With all the opto couplers it should be possible to move the HV part to a different PCB, box it, and only have safe voltages on the shield. This lacks the coolness factor, but you surely don't want arduino users to end up on the 'darwin awards' list ?

Yes, something like the RELAY SQUID

Actually there is a good amount of spacing between the HV and 5V. I have a few products that have the traces of voltage much closer! Everyone I work with in electronics is very careful and I am used to up to 480V power, so HV doesn't bother me at all, I just know to be careful.

I understand what you mean about doing a seperate box, however then there is no point of a shield at all, the only actual logic on the board is the arduino pins to drive the opto-couplers. Everything else is HV, so those traces are very small and only 5 of them and a few grounds. Maybe I will play around with the idea of a seperate board, I am already building one for a different project.

I personally like the idea of having everything on one circuit. I can put this shield on a arduino and put it in an enclosure and I have 4 circuit control in a very compact package with dimming too.

I like the relay squid, but for simple things it is just too darn expensive for me!

I wasn't talking about trace spacing !

More like:

left side of PCB: safe right side: hands off

Of course this is hard to do on such a small area.

Ahhh, yes. I am looking into encasing that end in epoxy for that reason. I will let you know how it goes.

Anyone interested in one can buy here also post, PM, or email if you have interest in a final version so I know how many to make.

I'm working up a spot-welder of the microwave transformer variety. It was a 1500 W unit, and I wound on 3 turns of #1 flex welding cable, so the current capability should be useful at 3.1 V off load.. I thought I'd do a cycle counter with a DueMilanove, using one d/o to drive an SSR I had on hand. The SSR uses an optoisolator, so its a safe approach. Still thinking about the way to set a pulse between 0.5 and 3 seconds repeatably. A 2 line LCD and push button inputs seem a little over the top though....

Brian W


Nice idea, but I agree with the others about mixing the AC with the lower voltage stuff. Many do not know the dangers of AC voltage, and the Arduino is all about experimentation, and making this stuff easy for people just starting out.

Just a suggestion. Build the AC stuff with the opto's on on a 2nd board, then use a small data cable to connect the two. Then the HV section could be put in a external box and protected.


Makes sense... I am working on a separate board as well. With a remote connection. The shield is working good though, I tested it with some light bulbs last night.

Any thoughts on the AC breakout? Molex connectors? Solder your own? Standard Outlets?

I would use screw terminals, or maybe you could build it into a power strip that uses standard outlets, then the end user does not have to use anything. They are cheaper than any box you could buy.


Standard Outlets?

Standard sockets for which country? And will the shield work properly on 240V, 50Hz power?

120v 60hz. The board needs to be setup differently for 240v.

If you have the time, I'm curious what would need to be changed for this to work with 240V/50Hz. Are you sill using the same schematic from your other post?

I've been looking at doing some lighting control myself and have been researching building something like this.



I know you are not directing this query to me, but using ONE Arduino digital output to drive a SEPERATE bolt down SSR means you buy just one thing - a 120 volt or a 240 volt SSR at whatever rating you need: 10A, 25A or 40A

This would be a safe, no brainer approach except for one small detail: opto-isolated zero crossing SSRs don't come cheap. Sadly.

Brian Whatcott

I agree an SSR would be ideal, except in this particular instance I'd like the ability to dim lighting.


240V/50Hz... is that 120V on 2 legs? I am not that familiar with that power.

Check out the data sheet for the opto-triac drivers. it has some 240V examples. Basically the same setup with some different resistor values between the opto-coupler and triac. The zero-cross can stay the same, just ensure you adjust the resistor value for the rating of the H11AA1 maybe 50k?

Remember, if you want to switch high current loads with this, your PCB needs to have large traces and a heavy copper layer to handle the current, even though the triac may be rated for 12A make sure the interconnects are as well!

betwys, I agree I use alot of SCR's at work. Like you said, the big downside is cost, and sometimes space. I really built this for someone that needs something low cost and simple to hook up. AC is a strange world.

This circuit is just about the same thing that goes inside a SCR, it is really just making the cost less by breaking it down and giving some more control.

I am working on the final version and am leaning towards a separate board rather than working with a shield. I personally love the shield idea, but I know it can strick some high voltage fears in people.