Andy1845c

I want to have some fun with my LED christmas lights. They are wired antiparallel, so putting a diode in the line causes only one half to light.

I want to use two diodes to seperate the ac cycles so I can control them seperatly.

I'm having a bit of a mental road block as to how to do this with transistors or fets.

I imagin there are similar circuits out there, but I can't figure out what to google.

Can this be done with only NPNs and diodes? Or will I need a PNP too?

Is there a term I can google that might bring up some relivent circuits? Is this a common way of doing anything else?

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audioguru

Since connecting a diode in series causes only half the lights to light then they are probably LEDs.
A high voltage diode plus a high voltage transistor can control each half of lights. An SCR can replace the transistor.
Look in Google for Color Organ which is a circuit that blinks lights in different frequency ranges.

The mains electricity is very dangerous. Optical coupled devices and audio transformers are used to isolate audio equipment at the input from the lights that are at the mains voltage.

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Uncle $crooge

things

...... yep, i think they are LED's But i don't think the LED's would be running directly from mains voltage, unless he had 300 or so of them. Try measuring the current draw, then maybe you could get a circuit diagram or something?

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HarveyH42

Here in the USA, we use 110 VAC, so its more like 30-50 LEDs in series. Great source of cheap LEDs after christmas ($2 a string).

Andy1845c

I looked up color organs. All the schematics I found look like they run off a single voltage. 120 or 12v ac. I would like to use 5v logic to control the 120v AC in my circuit. Further googling leads me to think the best way of doing this is with opto-isolators and SCRs.

I'm wondering for the sake if wondering if it would be possible to make a circuit like this with no isolation. Not safe i know, and I don't plan to do it. but I am curious.

If I take the 120v AC coming in, and use two rectifier diodes going opposite directions on the hot line, I will end up with pulsing DC, positive voltage on one diode, negitive on the other, referanced off the neutral or common line, correct?

Now If I added a 5v battery into the circuit to control the SCRs, can that be grounded on the neutral line?

I havn't found any circuits that do somthing like this. I can't think of what else uses 5v logic (or any low DC voltage) to control line voltage so I can look up circuits.

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audioguru

An SCR is a controlled diode. Its max power output to light bulbs is only half. A triac works with AC, delivers nearly full power to light bulbs and opto-triac driver ICs are available.

A color organ can easily be made to use a 5V power supply. It can activate a opto-triac driver.

Neutral is not used to ground circuits because a drunk electrician might have connected an electic jack backwards.

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Uncle $crooge

Andy1845c

But in a perfect world, the neutral could be used as a ground for a low voltage DC side of a circuit?

My goal is to only use half the ac cycle at a time. I want to take advantage of the way the LED lights are wired and be able to control each half of a string seperatly.

Could I use an opto-triac along with a rectifier diode? Would the triac ever turn back off if i did it this way?
I have not found an opto-SCR yet, but I am looking!

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mneary

If you're willing to bet your life that the world is perfect.

Andy1845c

lol, i'm not But I needed to satisfy my curiosity

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on1aag

Hi Andy,

You could use a line sync circuit and solid state relay.

http://www.edaboard.com/viewtopic.php?p=675914#675914

If you combine the two transistors of the TLP504 optocoupler
to form a bistable multivibrator you'll get a line sync.
Then you combine this sync signal with a signal generated by
a circuit that will do whatever you want the lights to do and
"AND" it to a solid state relay or even a MOC3023 optocoupler.
That's about it.

on1aag.

audioguru

Are your LED Chrstmas lights all in series?
Or are half in series and have one polarity and the other half in series are in parallel to the other half and have the other polarity?
Or is each LED actually 2 LEDs back-to-back and reversed from each other?
You don't know.

You won't find an opto-SCR because nobody uses it for anything.

A solid state relay is an opto-triac. they have only a few parts inside that you could assemble.

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Uncle $crooge

on1aag

Hi Andy,

Perhaps you could use two MOC3023's and two diodes, a line sync
is not really necessary to power christmas lights.

on1aag.

Andy1845c

Yep, like that.

I already verified this with diodes and a jumper wire on protoboard.
I just want to learn how to do it with no moving parts and see how far I can take this idea.



I was looking at those in the jameco catalog. Kinda expensive But they do look easy to use.

Those look interesting!

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kchriste

By NOT syncing, you could get a neat beat frequency fading effect if you drive the two TRIACs out of phase with a variable 55-65Hz oscillator.

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Hero999

I've heard you say that before and it's nonsense.

If your electrician is drunk then he might get the earth and neutral the wrong way round or even worse, he might get the live and earth the wrong way round and kill someone.

The reason the neutral wire isn't used as a protective earth is because, it won't always be at earth potential as it's used for carrying a large current and if it breaks the case of the appliance will become live. Also nasty ground loops would occur if the metal chassis of two appliances become in electrical contact with each other.

There is nothing wrong with using the neutral as the DC 0V terminal providing it's adequately insulated from the user and it isn't connectd to an external device (which would cause a ground loop0.

You could build the whole thing unisolated and use a small electret microphone as the audio input, that way you avoid having to use any isolation transformers.

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