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Beginner Project - Help understanding TRIAC circuit

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jcan

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Hello everyone, this is my first post here.

I am working on a outlet switch that can be toggled by an outside input (IR detector, Arduino, physical switches, etc...). I found a switch at Walmart that uses a photo-cell to control the outlet. I think it can be a good starting point for my project.

Can someone help me understand exactly how this controls the switch?
 

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What you show turns on/off by how much light is on the room. There a phoro-cell that changes resistance with light. It is in the middle picture. Clear lid with a red wavy line on it.

The real trick is to turn on/off power with out sending power into your (IR detector, Arduino, physical switches, etc...) and killing the Arduino etc...

You can look at x-10 modules. The idea is old but works.
 
How would you use a TRIAC to simply toggle a outlet on or off using an input signal from some outside source?
There are three pins on the TRIAC and I don't understand how to use it.

Should I use something like this?
 

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Dont open up the thing you bought, glue on a led over the photocell and paint round it black to keep out stray light, now when the led lights up your socket is off and when the led is off, you know the rest.

And you can do this with much less risk of blowing yourself up with the mains.
 
Thanks for idea, and tips about the dangers, dr pepper. I installed electronic communications equipment in the Army, so I have a solid respect for high-voltage and it's bite.

I think I saw this thing at the store and it seemed like such a perfect fix that I started to ignore other options. I've since looked up things like the SSR I posted a link to earlier.

Besides my original project, I'd still like to know what each part in that circuit is and why it's arranged the way it is, if anyone cares to explain it to me. :D

(Ignore the diagram I posted before, I took a bunch of screenshots and attached the wrong one)
 
The triac is a double thyristor, each thyristor acts like a diode when theres a gate signal present, 2 of these back to back acts like a switch, one that only needs a small gate current.
The photocell, resistor and diac are all part of the trigger circuit, dc (possibly from the green cap) goes to the diac and resistor, when the voltage accross the diac gets to about 20v it goes from open to short, providing the triac with gate current and it too turns on, switching on the load, when the ambient light increases the photcell resistance decreases and 'robs' drive current from the gate drive circuit just mentioned and the triac and therefor the load switch off.
The idea of the diac is so that the switch on point is the same either side (+ and -) of the mains waveform, this is important if the load uses a transformer, uneven switching is effectively dc and would burn out a tranny, it also gives a positive switch on for the gate drive further improving even triggering.
A better quality item would also have a couple of x rated caps or a choke to reduce rf interference from switching the mains, either that or some kind of zero crossing gate trigger circuit.
 
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