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Author Topic: Is this safe? (measuring 0 voltage cross on 110 VAC powerline)  (Read 943 times)
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Hi Guys,

I bought a TVS diode from futurlec. This is the description: "P6KE6.8CA - 5.8V Standoff Voltage - TVS 600W AC". I intend use it with my arduino to make an led blink everytime a 220 or 110 VAC power line crosses 0 volts.

1. Is this a dumb idea? say I set an analog pin as input, stick one end of the diode into the pin, and the other end to the main line... Will I fry my arduino? Will I fry the diode?

2. Do you guys have a better way for me to accomplish my task? Should I use a hall effect sensor instead?

I would appreciate any help smiley

Thanks in advance!
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I'm not so sure that's a good idea.

Besides, the LED would "blink" so fast it would appear to be a steady light.
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1. Yes, it's dumb idea. It'd finish arduino, your computer and you.
2. Optocoupler is other option, but for you I think, power supply transformer with AC 5V output would be only more safe to try.
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Thanks, I'm glad I asked. I appreciate the concern. Don't worry, I always ask before doing anything I'm unsure of. smiley

But for my information, please explain why I can't use the TVS diode. Isn't it's job to cut off power if voltage gets too high, and reactivate when voltage is within range? I figured it would only 'activate' when the voltage is between 6.8v and 0 volts. I wasn't going to directly connect the mains to the arduino lol smiley

PS. Just want to reiterate that I only want an explanation on why it won't work. Doesn't mean I'll go and do it anyway smiley I just want to know what the TVS diode can and can't be used for, and maybe a small explanation and recommendations on how I can get the arduino to detect 0 volt crossovers on the AC line smiley
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Thanks, I'm glad I asked. I appreciate the concern. Don't worry, I always ask before doing anything I'm unsure of. smiley

But for my information, please explain why I can't use the TVS diode. Isn't it's job to cut off power if voltage gets too high, and reactivate when voltage is within range? I figured it would only 'activate' when the voltage is between 6.8v and 0 volts. I wasn't going to directly connect the mains to the arduino lol smiley

PS. Just want to reiterate that I only want an explanation on why it won't work. Doesn't mean I'll go and do it anyway smiley I just want to know what the TVS diode can and can't be used for, and maybe a small explanation and recommendations on how I can get the arduino to detect 0 volt crossovers on the AC line smiley

Well as the saying goes "if you have to ask about dealing with 120vac power main, you shouldn't be messing with it".

As far as explaining why the component wouldn't work for you as intended, you would first have to draw us a circuit using it as you think it would work, then we can talk turkey.

Lefty

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What is it that you're trying to accomplish? Surely something other than blinking an LED at the zero crossing, which as already observed, won't be visible.
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a diode (or any 2-terminal device, for that matter) cannot be used as a switch.

Note sure I agree with that rather scoping statement. Surely diodes are used as switches when used as rectifiers.

I know, don't call you Shirley.  smiley-kiss
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If you simply want to detect zero crossings, use ...

Agree, but why are we interested in detecting zero crossings? What's the ultimate aim? There are zero-crossing detectors available for various applications, triggering triacs or whatever. I'd be temped to use a canned solution like that.
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KE7GKP,
That's exactly what I'll do. Thanks for being very helpful! smiley

Jack,
I'm trying to send signals through the main line while the voltage is 0. Just wanted to experiment if it would work. I wanted to use the led to see if I can get as far as detecting the 0 crossovers smiley I read somewhere online that the voltage on a regular line will be about 0 for 1 millisecond. Figured that if I used a fast enough baud rate, I could get a few characters through.


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A rectifier is a "switch" in the same way as a check-valve is a "faucet" (AmEnglish) or "tap" (BrEnglish). It doesn't equate IMHO.
To my way of thinking, a rectifier or a check-valve are passive and uncontrollable.
To my way of thinking, a transistor or SCR or Triac, or relay or toggle or pushbutton, etc. is an active SWITCH and "controllable" by a "3rd party".

From Wikipedia:

Quote
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC) which flows in only one direction. The process is known as rectification. Physically, rectifiers take a number of forms, including vacuum tube diodes, mercury arc valves, solid state diodes, silicon-controlled rectifiers and other silicon-based semiconductor switches......

http://en.wikipedia.org/wiki/Rectifier

Not so much disagreeing with your intended point, just that "a diode (or any 2-terminal device, for that matter) cannot be used as a switch." is a rather overreaching and technically not correct statement, that's all.


Lefty

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Jack,
I'm trying to send signals through the main line while the voltage is 0. Just wanted to experiment if it would work. I wanted to use the led to see if I can get as far as detecting the 0 crossovers smiley I read somewhere online that the voltage on a regular line will be about 0 for 1 millisecond. Figured that if I used a fast enough baud rate, I could get a few characters through.

@heyarn,

Technically the voltage crosses zero at a point in time, so it's a question of how close to zero do we consider to be "zero". Have you considered what technique will be used to modulate the information onto the power line? What carrier frequency will be used? Something more esoteric like spread spectrum? I wouldn't consider this a trivial undertaking.

X10 was mentioned, I installed some of that years ago and it worked fairly well at the time, but lately I've found that it's just about useless in my house due to (a) surge suppressors, which seem to nicely filter out the X10 carrier, and (2) fluorescent lights with electronic ballasts which evidently put enough hash in the lines to prevent most of the X10 signals from getting through.

If it were me, I'd look for some pre-engineered module, I think there are some out there for communicating over power lines but am not conversant with them (GIYF). Why re-invent the wheel, someone has probably already done a better job at it than I could. Radio is another possibility, there are multiple alternatives out there. I've had great results with XBees, but I'd have to know more about the application (we haven't yet discovered the ultimate aim here) to be able to say if they'd be appropriate.
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KE7GKP,

It seems that you have had experience with the TDA5051. Will this module work with the arduino easily, or will I need a bunch of electronics to make it work with? Any tutorials? smiley I read the link you gave me, but it is more focused on vwire than how to actually hook it up to the arduino. smiley

My ultimate goal is to be able to automate the outlets in my home. So it has to be small. I've tried the tx/rx433 links, but the range is bad indoors (I haven't tried to put copper wire antennas yet and hopefully increase the range. I'll do that this afternoon.)

Thanks !


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I have a project in mind to implement some X10-like functionality using XBees. I'm not planning for it to fit into an outlet, it'll be an external box that lamps or whatever would be plugged into. Each box could control several independently addressable outlets, right now I'm actually just thinking about two per box, maybe one with a triac and the other with a relay. No more details yet, just something in the back of my head. First I want to experiment with switching compact fluorescents with a triac, to see if that turns out to be a bad thing for one or the other.
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