I would never use triacs to switch power with a micro unless there was a specific reason that a triac was required. I would use a relay which provides as good as isolation as using an optoisolator and you don’t have the risk of getting shocked by the tabs like on the triac in the picture. Also triac produce heat and switching large loads generates a lot of heat. Relays are a proven method that is used in millions of homes in everything from microwave ovens to central heat and air.

well thats very basic.

if you look at a commercial product there HAS TO BE a distance between the logic(5V) circuit and the 240V circuit.

Obviously arduino users donÄt know about this…

Relays are good for on/off setups, but what if folks want to do something like dim an ac light?

…I just wanted to point that out since you know how fond the Arduino crowd is of blinking led lights.

Great proof of concept. Would I ever use it? No. Never. Always be excessively careful when working with high voltages. That being said, if it’s ever updated and the problems fixed, I’ll be buying a few of these.

FYI
I just ordered 10 pieces of 39MF22 integrated Solid State relays.
0.9A@600V With 4kV isolation and zero cross circuit.

my case I need to control a Elevation/Azimuth CCTV motor for controlling an Sat dish or 13cm HAM antenna. This is a 24VAC unit so voltage is not a real issue. I probably design a separate PCB and not a shield just in case I need to control something at 230VAC

yeah, there’s a right way and a wrong way to do it. i’d say you can design them on the same board if you do it right, and this isn’t being done right. unfortunately there’s no schematic or board layout image provided, but from what i can tell, the optoisolators are actually not performing a large part of their function here: the HV trace goes right across one of them, removing a lot of the inherent transient protection they’re supposed to provide. the layout is pretty terrible from the safety and protection standpoint, and honestly it’s not hard to do better.

I have been doing some research on my next cleaner/safer version of my grow box controller. Though codes still varies my city/state/country, the consistent rule I have seen is low voltage and high voltage can co-exist as long as the solid 16 gauge wire is used for both low/high voltage connections.

That being said, for safety’s sake I would recommend moving the high voltage completely away from the low voltage since trying to “safely” reattach one wire while the system is live is definitely not recommended.

With respect to HV this could be a “safe” solution, though I probably wouldn’t start selling these without setting up a LLC or have several pages of lawyer talk in the order form.

This is one of the rare cases where I have to agree with the safety crowd – electricity out of the wall is nothing to play around with, and 120V REALLY sucks to get shocked by. I got zapped around the age of 6 by a loose VCR plug. For those not familiar, the instant you touch it, the electricity tenses your muscles, more than likely making you hang on even tighter. I was stuck for atleast 5 seconds, let out a loud scream and eventually was able to sort of stumble back away. My lips were cold and pale for a good bit after..

A circuit like this should really have a fuse, perhaps even a thermistor.

Quite honestly, this should never go to market, be used, or even be handled in it’s current form.

First, use isolated tab triacs, it’s a no-brainer.

Second, at least put a lexan shield around the entire high voltage area.

Third, heat-sinking will be an issue, so include some in the design.

Fourth, use proper isolation technique, such as routed slots between the high and low voltage sides.

That being said, it is innovative, and if you fixed the safety issues, added a regulated 5V power supply, and had it properly potted in an enclosure with guarded screw terminals off the topside for the AC, I think it would work quite well.

mmm, tubes…..

Plasma tweeters come to mind :D

@Skitchin:
Aren’t you glad we don’t use 120V DC, hehe… Needless to say, you need to know what you are doing here. DC is pretty easy stuff, AC gets tricky, and not knowing the basics of either will have consequences. Nonetheless, this is a semi-useful shield if it’s in the right hands.

The main problem is the TRIACs and their tabs. The simple way to improve safety is to use insulated tab TRIACs. These are a bit more expensive, but much safer. Whilst you are at it, also use zero switching opto’s

Darryl

I’ve seen two AC projects this week missing the same thing: a fuse. That magic little glass device will keep your house from burning to the ground. Try to match it to your intended load too, not the absolute max of the circuit.

you shouldn’t be so afraid, it has optotriacs, that’s pretty safe if you keep your hands off the tabs, fuses are a good idea, but the board is isolated from the electronics.
this is much safer that another project i did, it used a transformerless power source and all the project was floating in the AC voltage, so i could switch the triac directly.
if you keep your hands far from the wall voltage you shouldn’t have problems at all.

@mosheen – Correct.

Don’t forget to put them in your DC projects as well.

A must if batteries are involved.

@ianc, DC voltage contracts muscles making it very difficult to pull your hand away. An advantage of AC voltage is that it doesn’t share this property and is the reason you were able to jerk your hand away.

People just need to fucking die! Whatever happens to achieve that goal is fair play.

We built several similar boards for an art project supporting 8 channels without problem. Our boards had screw terminals for each channel. These were NOT shields though.

My main comment would be to take the plug off the shield and connect it via cord. I wouldn’t really want to be holding the Arduino and shield to provide the necessary counter-force while I plugged it in.

Solid state relays are the only way to go for hobby projects. They’re all over the bay for 5-10 bucks. Not even counting the advantage of zero-cross switching, the convenience, safety and reliability is well worth it.

The safety concerns people have mentioned are quite valid, especially that the tabs should be isolated.

The real issue, though, is mounting– a shield is really not a very safe way to build something like this, for two reasons.

1) Since there are or may be pins sticking up from the Arduino (or other shield) underneath, those could get close to the AC side of this board.
2) Arduinos are not typically mounted to /anything/, in spite of having standoff mounting holes! So, this thing will be skidding around a tabletop or held to something with rubber bands and/or hope.

This is not a dangerous idea per se, it’s just a matter of implementation.

To be fair – the developer was doing his best, and while there are plenty of people that can do better – we all made simple errors when we started out. Some of us had mentors to put us right, and others… well they’re not here now.
Keep this effort within sight at all times, and remember when you do fire it up (no pun intended) – make sure it is well isolated, fused and ideally on an earhtt leakage circuit to protect the vulnerable that are downstream fromthe box. Kids, pets and falling stuff all have the innate ability to find live circuits faster than a sparky.
Making non-lethal mistakes is as good a way of stimulating positive criticism. Just don’t let your ego run away yet – or you may face liability and insurance problems you never dreamed of!
Good luck – and keep on developing stuff.

To people who are freaking out over using triacs: They have been used in $5 touch lamps for many years now, and they utilise the shitty-est capacitive sensor circuits.

Anyway, regarding this project, it’s hard to tell from the photo, but I don’t think I’d be satisfied with the layout. I would probably tear up the PCB design and lay them out for better physical isolation.

For the circuit design perspective, again it’s hard to tell without seeing the schematic, but it appears this thing is using MOC3022 optos (the white 6-pin DIPs). Those are rated at about 400V, which provides adequate electrical isolation, IMO.

… And to all those suggesting relays, I’d like to see your version of dimming…

@Agent420: No problem, let the relays do PWM and implement an automatic relay changer with a 1000 relay magazine.

This “wuss” had many years in power control (240/415, to 100kW) including lots of live board work, and this project seriously sucks. There is nothing wrong with the *idea*, it’s done all the time, it’s the *implementation* that gives me the willies.

@burnsy
Instructive redesign is a really good suggestion.

Triac or relay? That depends entirely on the application.

@Matt
“I tried to go faster, but I quickly started frying relays.”
Which is why frequently operated relay contacts are fitted with a CR snubber to minimise contact arcing, and you have to do something similar with triacs and SCR’s if the load is anything but purely resistive or they will stick on. The current and voltage *both* have to go below threshold before the triac will switch off.

@Manfre
Edison’s marketing myth from his battle with Tesla resurfaces. Muscles effectively rectify by contracting whichever way the current is flowing. The primary determinant is what happens when you get the shock and your muscles contract – is your hand going to grip the conductor, or move away? So if you *must* touch, always test with the *back* of your hand (after using your trusty neon screwdriver). And yes, I have given myself a richly deserved black eye.

@kpetoh
Unless of course you are in a lightning-prone area where a 1930′s relay will outlive a dozen semicons; or you are switching a reactive load (when triacs will often stick on); or DC; or where a shorted triac could produce a dangerous situation; etc. Triacs and SCR’s are also prone to dv/dt firing. The failure modes of relays and triacs are different, but the difference in overall reliability isn’t as great as some seem to think.

@Tachikoma
400V is not enough for a 240VAC supply – 1kV minimum.

@Agent420
Okay, so this is for dimming. So where are the switching supression components? I have built light dimming racks for theater use and consider an earthed metal box for all the high voltage to be mandatory. Recycled computer power supply cases, available free from your local computer shop, are near ideal for this sort of project.

A word about ELB/CBR/’safety switches’; if you are not well earthed and manage to touch both the active *and* neutral you are simply part of the load and will FRY. ELB’s also fail quietly and I’ve found more than a few that won’t trip at all. An ELB is not your main protection, that comes from good practice, the ELB is your last gasp reserve ‘chute and if that doesn’t open you’re toast.

If OP is selling this I hope he understands that his liability insurance will not cover inherently unsafe design.

@agent240:
not likely, most definitely. the american plug makes contact before the contacts are out of user’s reach. the european plug is recessed so you can’t get your fingers near the hot pin. and at least with the 3-prong one not the pins but the plastic part carries the mechanical stress.
but then again, 240V needs better insulation than 120V. in europe, you don’t see lamp sockets with paper insulation either.
well, ok they might have them in italy, because your electrican’s cousin good them from a friend in the us…

Stupid thing! But at least now the Arduino fans will get the Darwin awards they deserve. Triac circuits connected to mains should be kept away from young children.

And you’re not saying the creator of this didn’t know what he’s doing? You should. This board design breaks the basic principles of high voltage safety. Check any high voltage design manual, and you will see how you should respect isolation distances between low and high voltage parts of a circuit. This board absolutely does not.

Just a note about shock hazards. I follow the rule of one hand kept in pocket when working with live voltages present, helps to keep you from completing a circuit. The other thing is that most people killed by getting shocked were not killed by the electricity itself, but by their reaction. You are standing on a ladder changing a light bulb and the switch is still on, you get shocked, what is your reaction ? To jerk your hand back, losing balance you fall off the ladder and break a bone or worse. Happens all the time especially in factories near heavy machinery.

To the best of my reading so far- the “Hack by itself” here is expanding what a “shield” board can do. I’d call it a “Proof Of *CONCEPT* Prototype” And, as such, the original builder gets an “attaboy” round of applause for advancing Hacking! Safety is what speaking for myself only, I describe as situational. Different rules for each situation. Hacking is a situation divergent from “appliance operation” Are we not Hackers?

There’s a phrase that appears in my mind EVERY time a comment thread veers to Paranoid or Darwinbaiting extremes. **Be careful, but not too careful**

And, I owe a beer to someone who knows it was them, that put it on wall signs in a Hackerspace:)

There’s another sort of wisdom that goes in and out of fashion in Design Science itself. It’s called Design For Usage. IIRC there were/are several variants of that as textbooks,and the ones I read of the type, influence my Hacking for the better. I point our thoughts to the comment by tantris RE: using those Christmas Light” switches, and an Arduino controlled LED.

As in so listing, tantris has applied the “less risky” path. Hacked something an Industrial Designer who may have applied the “Design For Usage” courses to making UL approved- in a way that does not appear to lower that safety factor we presume is in an approved shrinkwrapped unit.

Hacking lives-or we DIE in wrongly choosing which approach we use. Shrinkwrapped with non-invasive=least risk hacks- or this EXCELLENT for it’s “Lab POC prototype status” AC Shield= Darwinbait to the untrained/unlucky.

Kudos to the Hackers of both approaches.

Ok, you “safety” guys are missing a critical detail, this is a part, not a whole solution. Whoever uses this part needs to add the obvious safety features to the solution they are producing. A fuse and a proper enclosure are certainly required for a 120v solution but they don’t belong on this part anymore than they belong on every individual relay. Assuming someone makes a little black plastic box with this and a fuse inside and a plug and socket on the outside to make their christmas lights flash joy to the world in morse code or whatever they’re doing with it, where’s the danger ?

The same idea is used on heater controllers that are used for plastic injection molding systems. Analog circuits or a microcontroller sends a signal to an opto-isolated triac driver. These are used in 240V AC three-phase standards. the Triacs can handle up to a 40 amp load (in my case). Two protection circuits are used, first a standard set of fuses on both sides of the AC, then a relay on both sides of the AC, also controlled by the micro. The micro is located at least 1/2″ away from any AC. On the board, standard separation from AC line to line is 250 mil, as well as AC to DC, all 250 mil (quarter inch). The board is covered by a heatsink, attached to the back of the Triac (isolated tab). If the triac gets too hot, it will go into what’s called a thermal runaway. If it gets shorted, it will also put out full power, but if that happens, that’s what the relays are for, if the micro senses something out of the ordinary, such as excessive current, or if you have a temperature sensor or even a light sensor, you can have it automatically kill the relays before damage is done. Of course, this would take more board space, and a good knowledge of basic routing practices for pcb’s.

Even though I add the occasional breaker to power panels with the power still on, I concur on doing this the safe way, including creepage / clearance on the PCB layout for optocouplers. There are reasons this is in electrical codes.

One reason is lightning strikes to the power-line network. Want your project and computer to still work after a storm? Whoops, forgot to unplug it.

Another reason is that since power lines go down in storms, tree branches fall, pole transformers fail (I’ve heard the occasional boom), power poles get hit by cars and tools or metal ladders can fall on pole transformers, it’s reasonably possible for the (in the US) 1.25kV feeding the power-pole transformer outside your house to get momentarily into your home’s power wiring. For instance, our power-pole transformer also feeds a house across the street. About two years ago a dump-truck with the dump bed left up caught the power lines crossing the road and ripped the transformer right off the pole! Hard to guarantee isolation when that happens.

Oddly enough, the people writing electrical codes don’t seem to like homes catching on fire or people being electrocuted when these sorts of things occur. Wimps.

I hope “The Cheap Vegetable Gardener” was kidding about 16 gauge wire taking care of safety.

A fuse will help prevent fire but won’t save you from shocks. It only takes milliamps to kill, which won’t pop even a 0.5A fuse. And it takes amps to make me turn in my status reports.

Hacking lives-or we DIE in wrongly choosing which approach we use. Shrinkwrapped with non-invasive=least risk hacks- or this EXCELLENT for it’s “Lab POC prototype status” AC Shield= Darwinbait to the untrained/unlucky.

Kudos to the Hackers of both approaches.