Imp enabled A/C switch

This is the latest prototype of my Imp enabled A/C switch. Essentially a Power-Tail with all the Imp hardware contained inside. Handles up 5A, and is made for switching low power items. I used a solid state relay, which works very nicely, and doesn’t make any clicking sounds when it switches, and saves a ton of space. The case is a 3COM PoE injector, and works very nicely for this prototype, as I am still trying to source an enclosure.

I’d like to get this project to be as small as possible, and then make addon modules that you could daisy-chain back to the master, and use a single Imp to switch several others.

The circuit still needs a fuse, and a few other items, but it works as is. I have a smaller version of the ACDC on order to bring the size down even more.

looks pretty sweet.

How is the imp/april board powered?

These are the types of projects people are looking for. This is what gets people thinking about new projects and ideas. Thanks for posting what you’ve done.

The project I just completed has the imp/april and a TI serial to parallel chip to control 8 solid state relays using only pins 1 and 2 (UART12). I’m working on the project presentation to show with photos, schematic and code. The TI chip is addressable so it could be expanded to 64 digital outputs using 8 of the TI chips. Solid state relays are expensive, but ebay is a place to get used ones pretty cheap. I’ll be testing it fully this winter for outdoor Christmas light displays.

I don’t think I’ll ever use the imp or any other remote controller for things that are critical, like my home furnace. Failure of heat control in Minnesota, when it’s -20F can be serious.

The large black component in the middle of the board is a 3.3V ACDC convertor. It works nicely, and connects to a board very well. It isn’t extremely cheap, and it there are smaller options that I am looking at. Here is the datasheet.

I just got another version in, that is significantly smaller and I am hoping to install at a right angle to the board.
That one is even more expensive, but very small and powerful. For my own projects, a few more dollars isn’t a big deal, but in mass production it would be. It may turn out that using a 12V ACDC along with a 3.3V buck like the april has is cheaper… I need to look at it.
Using a 3.3V ACDC is very convenient. I’ve got a few more enclosures that are much smaller than the one show above, and I am attempting to get the circuit built inside.

I’m going to use mine to power holiday lights as well… probably try to do some cool stuff at halloween.

These are nice ac/dc circuits, but except for the very expensive ones they need significant extra external components + good EMC cleanup on the mains side => i think that it’s probably much cheaper to use a small low VA transformer, some diodes a cap and a linear regulator. Won’t have the efficiency of the switched ones but for these currents that doesn"’ make much of a difference wrt heat generation and the power signal is much cleaner. Compared to the larger ac/dc ones, takes about the same volume for at least half the cost

@vedecoid Do you any example schematics and parts list for what you described? I’d like to start building a board for this circuit, probably pull the unnecessary parts off of an April and add the ACDC and SSR. My electronics knowledge is relatively basic… I took a few classes in DC electronics 19 years ago, so I am trying to learn everything I can.

Here is another SSR to look at if anyone else is working on something similar. It only requires 3mA to drive the SSR, so a single Imp pin could handle it… You can switch up to 3.5A. Downside: Its $19.90.

New version. I packed one inside an old (pre-magsafe) Apple power adapter. It is a very tight fit. I used one of the Amber boards that I had printed, and you can see the blink-up circuit is available from the outside. Also used a Recom 5V ACDC to power the Amber board, and a Crydom SSR. Right now I am working on mounting this inside the post light outside my house, and put something fun inside, like Neopixels. Then spread the web address around to the neighborhood kids and let them blink the light. I might mount a plastic jack-o-lantern on the post and blink that for halloween. Still testing what kind of brightness I need from the internal lights.

And another one… this one is actually made with components completely available from Digikey (except for the Amber board), and I am quite happy with it. Recom 5V ACDC, Crydom 3.5 Amp SSR that can be driven without a transistor by a single imp pin.

Hugo, I’d be very happy to hear any critiques of the layout. Any obvious issues? The Amber board has the LDO, and the Recom AC/DC seems to be outfitted to supply pretty clean power. I’m supplying 5V at VIN.

The amber board is laying face down on the bottom of the enclosure. The Recom ACDC is laying upside down on top of it, with the SSR in between its pins.

Actually, I have a question. Something doesn’t seem to be quite right with how I am driving the relay. The SSR has a + & - pin on the DC side. I have the + side tied to 3.3V from the Amber board, and the - side tied to Pin 9. When I drive Pin 9 Low, the relay switches on, which I expect, but when I drive it high, it doesn’t seem to shut the relay completely off. Do I need to configure Pin 9 differently? This is the first SSR that I am driving with just the Imp. This SSR requires 3mA at 5V, and I believe the Imp 002 can supply 8mA per pin.

Do you have a resistor between the two relay control wires ( between + and - )?
Try a 2.2K ohm resistor there if you don’t have it already.

See my instructable schematic…

I’m using 5 volts in my circuit … thus the 750ohm resistor, but you can see how the resistor equalizes the voltage when the negative is not being pulled low.

Also, the ssr load needs to be enough to overcome the leakage of the solid state. It might not work with LED christmas lights, but will be ok with incandescent lamps. That problem shows itself when trying to turn off the load.

Still not switching off. When I switch it off, the AC voltage drops to around 30V instead of fully switching off.

What kind of load are you switching?

At the moment, an Arduino with a 5V AC/DC. Way under the 3.5 Amp limit.

I mean the load that your ssr is turning on and off. Its a 120vac thing you’re turning on and off?
You can’t just measure with a voltmeter. You need a real load on it.

Yes, the load is an AC/DC converter powering the Arduino through the barrel jack. When the relay is “off” some current still flows. I did have it connected to a lamp, and when “off” the light was on but very dim. Not sure exactly what is going on there, or if I have a bad SSR.

If I plug a lamp into the switch with an incandescent bulb it switches on and off normally. AC voltage when off is 0. If I plug in a lamp with an LED bulb or other lower power device, the switch does not fully shut off. I measure around 30VAC across line and neutral.

Bingo! That is exactly how solid state relays work!

If you don’t want that to happen, you will need to use a coil-type relay, not solid state.

Here is the ‘over-my-head’ explanation…

You might want to try a ssr dummy load resistor, but it may not be right for your box?
Google: solid state relay dummy load

I think I just answered my own question by reading this:

There are two types of SSR’s and I have a Zero Cross SSR. It is made to control resistive loads, and not inductive loads, thats why it works fine on the incandescent bulb, but not for the LED or wall-wort.