Frequency sensitive lasers

[DaJe]

So I was talking to my brother about some CCFLs I have, and the sound sensitive devices I also have for them. I was telling him how they could be placed anywhere at all, especially with my extra long cable I soldering, and how I can adjust their sensitivity. But what would really interest him is if he had lights that were responsive to different frequencies. Perhaps a red laser, a blue laser, and a green laser, all pointed inward to form any color. He does a lot of audio and music work. He always needs to make sure that it sounds just right.


So basically, anyone have ideas on making lights that are responsive to different frequencies? Perhaps I could modify an already existing sound sensitive device, as it already has a microphone, is sensitive to decibels, and can be adjusted. I'd just need to come up with some way to add in frequencies. It's kind of be like an equalizer in a way.

[dgrmkrp]

Hmm.. I have an idea: there is a nice winamp plugin that makes the leds on the keyboard blink. keybvis if I remember correctly. Take a bad keyboard or a cheap one, kill everything except the PCB and de-solder the leds, atach some leads and take the signals to another board, with the led signal commanding some tweaked transistors: these will allow higher currents and you could attach anything to them.. light bulbs, lasers, many leds.. this one is in design right now, shoved in a corner of my hdd.. in waiting mode.. but if someone wants something similar.. The nice think about the plugin is that it allows some settings to make the response better.. bad thing: 3 bands only..

[xmastree]

What input do they require? Just audio? It shouldn't be difficult to use a speaker crossover to split the audio into three frequency bands.

[DaJe]

Whatever kind of input would get them to work right. He would need to to match up the right frequencies for when he's doing audio work. You would have to explain anything in detail though, as I have really no idea what to do.

[xmastree]

What are these 'sound sensitive devices' you mentioned in the first post?

[DaJe]

This


http://codeinsurrection.com/pics/DSC_0400.JPG

http://codeinsurrection.com/pics/DSC_0401.JPG




It has a microphone

http://codeinsurrection.com/pics/DSC_0402.JPG




And a thing to adjust how sensitive it is

http://codeinsurrection.com/pics/DSC_0403.JPG





It's originally for using with lights, but any 4 pin molex device can be plugged into it. I've tried it on fans before too.

[dgrmkrp]

I don't think the thing in the pics is activated by frequency, but by sound intensity (->>db), so the sensitivity setting is useful only to "catching" sounds in a quiet environment.. usually low frequencies activate it, but if your friend is into music, at high volumes the thing won't be acting as an "equalizer", but more like an on light..

You would need some way of taking the actual signal, split it in bands, feed the signal-is-in-the-band signal to.. transistors, and again you can put whatever light you want..

I think you should study OP amps :) Mixed with capacitors, resistances, transistors and some wires you could have an N-band light show :)

Again, I think the sound sensors in the pics aren't good for this application, but rather as they were intended: make a CCFL light up on the beat :)

[DaJe]

That's what I said in the first post, they're only sensitive to decibels.

[dgrmkrp]

OK, forgot about it :) my bad :) Still, the difference between sound pressure and frequency is fundamental here.

You should look for a circuit like this:

for each frequency band that you want you need a voltage follower (opamp with output connected to inverting input, signal connected to non-inverting input, needs +/- voltage supply to work properly), so that it takes the input signal and repeats it without taking anything from it. All voltage followers are connected in parallel, so they get the same signal. Parts needed: 1x opamp/input stage

The output of each follower goes in an active filter, composed of 1 or 2 opamps, in an active (bandpass) filter configuration (use winisd beta or alpha to calculate the required capacitance and resistance for your frequency range) and some smaller parts.. Parts needed: 2x opamp, 2 Capacitors, 4 resistances for middle band, or 1,1,2 respectively for the first and last bands (a banpass filter is made from 2 filters, one high pass and one low pass, but at the extreme ends of the human frequency range you only need the low pass and high pass, as the human physiology does the rest.. ). Still, in case the music has not been filtered and has frequencies above 20KHz too, the last upper band should have a band pass filter too to avoid finding the light strobe frequency at which you can cause a seizure..

The output now has only the desired frequency range... but, this signal needs some further transformation to be used as a command signal, so another opamp is needed, in order to compare the level of the signal to a given voltage, which you can tweak from a pot or have it fixed. This would be better supplied with a normal continuous current, not +/-, as we don't want the response to go bellow 0V (google around to find exactly the type you want, as there are some with fast response or with an inertia - hysteresis, and I don't know how you like your lights flashing ;) ) This stage makes the signal rectangular in nature and it should be prepared to drive the gate or the base of a transistor (the current needs to be tweaked as to never give the transistor too (much) less current, so you need a value that will make the transistor 'open' 100%. the rest of the time, it should only be pulses of 0V and a positive voltage... make sure there is no current the rest of the time.. a capacitor removes all DC when placed in series. This way you get light pulse and a pause when there should be one). The transistor should be supplied with normal DC too and is used, like I said, to drive a load that is bigger than anything a small chip could drive.. Using a high wattage/high current transistor would allow making a light show with normal incandescent bulbs :) Parts needed: 1 opamp, a pot, some resistances and a transistor.

Now, maybe I missed a part.. I wanted to make a quick schematic, but for some reason I get all kinds of errors.. Software bugs.. my bad.. I tried explaining as best as I can, but if someone can help some more.. I bet there are commercial products that do what I said above and maybe they are even integrated so as to have all circuits in a really small place.. But they could be expensive.. Also, depending on the number of bands, this can be really cheap to..cheap. I can buy parts like these for a few cents a piece, so I would need dozens of them to make a dent in my wallet..

Have fun trying to figure out if this is worth it or not :) This is a modding community, so a DIY product is so much cooler than buying an expensive light show machine ;)

[DaJe]

I of course would love to make anything myself. The bigger the challenge is, the more fun it will provide. It'll take me a minute to read throguh all of that and comprehend it. Anyone else, feel free to try to explain it as well, with diagrams if you want too. I really have no idea about any of this, but I'm going to try to figure it out.