Tell me more ×
Electrical Engineering Stack Exchange is a question and answer site for electronics and electrical engineering professionals, students, and enthusiasts. It's 100% free, no registration required.
up vote 1 down vote favorite
1

I'm working with the following op-amps:

LM308AN LM358P UA741CP

I want to make a small box that will control the power to any string of christmas lights based off of music that is playing. I would like it to pulse with the base. I want the input to be the signal from the headphone jack of my computer and I want the output to be something that would operate any light that could be plugged into a wall outlet (120VAC?).

share|improve this question

2 Answers

up vote 7 down vote accepted

Sometimes, simply stating what you're trying to accomplish is better than asking the question you think you want to ask. This could very well be the case here. So, indulge me as I try to restate your situation and provide some sort of answer.

You have a headphone jack with some music on it, and you want that music to control some lights. You probably want the lights to blink or pulse with the music. Right?

This type of device is called a Light Organ. There are many forms of light organs, but I assure you that none of them use an op-amp driving a relay. There are several reasons for this:

  1. Relays don't operate well from an audio signal. They really want a signal that stays on or off for a while and doesn't just oscillate like an audio signal does.

  2. Relays can't dim a light. They can turn one on or off. Not so good at dimming.

  3. Relays would make a lot of noise, chattering away with the music. Not a pleasant sound.

I would recommend that you Google for "Light Organ". When I did, I came up with 65 million pages. Some of them are selling completed units, some have kits, and some have schematics.

I hope that helps!

share|improve this answer
He really really really needs to be encouraged to tell us what he is trying to achieve.Your advice may be "utterly spot on", an d quite probably is, but he may have something quite different in mind. Your "light organ" reference may create an epiphany - or just hatch more wild geese for us to chase :-) – Russell McMahon Jul 22 '11 at 3:26
1  
@Russell McMahon But I excel at Wild Goose Epiphanies! – David Kessner Jul 22 '11 at 14:47
@RusselMcMahon, why not take the time to ask for more information on the question and wait for an answer instead of guessing with David at to what the OP wants. If they will not be clear there is no way that you can answer a right answer, instead it is prose for upvotes. Lets get good questions then write great answers. – Kortuk♦ Jul 23 '11 at 14:45
@Kortuk He did ask for more info in his answer somewhere else on this page. – David Kessner Jul 23 '11 at 15:08
@DavidKessner, I flagged him because you are automatically flaged. That is just it though. An answer asking for more information in an answer should just make up a comment. Wait for more information, a major update could make both your answers invalid and then you have answers that just need to be deleted, if they are well written they normally have upvotes and hide answers to a real question. – Kortuk♦ Jul 23 '11 at 15:32
up vote 2 down vote

* See important addition at end *

You have not provided enough information to allow a good answer. Provide more information and I'll upgrade this answer progressively.

You don't explain what you are trying to do. Do you you want the relay to operate on sound peaks, or when sound is present at all, or to latch on when sound is detected , or ... . You MUST provide a clear explanation of your actual requirement.

Saying that you had the '308 working and that now it isn't is like saying that "My car was running but now it is broken, what's wrong with it?"

However:

  • The LM308 is a nice opamp but far better than is needed here.

  • The LM741 is an OK opamp but has characteristics that will make it VERY hard for you to use here.

  • The LM358P is just what you want - once we know what it is that you want :-)

There is a 95% chance that we can tell you how to do what you want using an LM358 once you give us enough details.

What are the relay's voltage and current ratings? They should be marked on it. Maybe also coil resistance, brand, model etc. The more we know the better.

Help us to help you - at present your question is unanswerable. An explanation of what you are trying to achieve is still needed.

A catalog of the D2w203F and similar relays is here and the datasheet for the D2W203F relay is here

This is a somewhat expensive SSR ("Solid State Relay") with 3-32 VDC control input BUT AC output using an internal TRIAC. It's rated for switching from 24VAC to 280 VAC at 0.06 to 3 Amps. It is not suitable for controlling DC.

It could control AC powered Christmas tree lights either by mains switching or at low voltage. The 2A rating should not be exceeded.

This relay is made only for on/off operation. It may be able to be used to modulate" the lights in time with the music, if that is the aim BUT the TRIAC switch will always turn on for at least half an AC cycle so use as a "color organ" would be limited.

Tell us what you want and we'll tell you what you need. :-)

share|improve this answer
There is some audio band filtering involved, so LM358 can be used to make low-pass, band-pass and high-pass filters. Search for schematics of opamp based filters. Another cascade will be rectification, say with diodes and/or more opamps. Then may be even logarithmic amplifier. Lots of analog processing. – Rocket Surgeon Jul 23 '11 at 1:05

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.