Beat Controlled LEDs

[Edude03]

Hello everyone!
I'm going to buy a Acrylic computer case with lots of LEDs soon.
Since this computer is for lan parties and such,
I want a cool effect like lights that flash to the beat,
Anyone know were I should start for a project like that?
Thanks,
Michael

 

[aniruddha]

Hmmm....
do you mean something similar to those different colour LEDs that glow depending on frequency outputs and the number of LEDs of a particular colour glow depending on amplitude of output of that frequency?

Well say you've got an option of 5 colours ... R/O/Y/G/B.
You could use band pass ckts with different BW depending on frequency zones.
eg.  300hz-700hz, 700hz-1.3khz, 1.3khz-2.1khz, 2.1khz-2.9khz, 2.9khz-3.4khz

Now the no. of LEDs connected down the ckt. after the BP filters will glow depending on the amplitude of filter output. You could use an ADC say ICL-7109 or just a ladder of comparators (of course this is bulky & costly but simpler to build) LM 339 would be perfect with inverting inputs receiving reference vtg levels from a resistor ladder (acting as vtg. divider). All the non-inverting inputs be connected to the filter output. Further the comparator outputs are connected to different LEDs of same colour.

 

[audioguru2]

Now the no. of LEDs connected down the ckt. after the BP filters will glow depending on the amplitude of filter output. You could use an ADC say ICL-7109 or just a ladder of comparators (of course this is bulky & costly but simpler to build) LM 339 would be perfect with inverting inputs receiving reference vtg levels from a resistor ladder (acting as vtg. divider). All the non-inverting inputs be connected to the filter output. Further the comparator outputs are connected to different LEDs of same colour.

You have described the LM3915 bar-graph LED display driver so why not use it? Its 10 outputs have constant current circuits.

 

[aniruddha]

hmm.. well i didn't suggest a LM3915 because... I didn't know about it ...
he he he

 

[audioguru2]

Hi Ani,
The LM3915 has logarithmic steps for audio and light levels. Its steps are spaced 3dB apart so the range with 10 LEDs is 30dB. Two ICs can be cascaded for a 60dB range.

The LM3914 has its 10 steps spaced 10% apart so it is a linear voltmeter.

The LM3916 is an audio VU meter with different spacings between its steps, but I prefer using an LM3915 as a VU meter.

They can all be used as a "moving dot of light" or as a bar-graph.

 

[Edude03]

Thanks guys,
I don't really need multiple colors though.
My case only has blue leds and I want them to flash only to bass pretty much,
I also need to be able to switch between Flashing, On, and off, but I believe I have the covered,
How much electricity do you think a circuit will draw?
Since this is a computer, I really only have 5V/12V to play with.
Thanks again,
Michael 

 

[audioguru2]

Blue LEDs are about 3.0V to 3.5V. Three can be connected in series and with a current-limiting resistor and connected to 12V. The current for each string of 3 LEDs is 25mA.
A little transistor can drive up to 7 strings on and off and can be driven by an opamp lowpass filter for the bass.

 

[Edude03]

Thanks audioguru and everyone.
Audioguru, sorry if this seems lazy but I really want to finish this by saturday, so could you possiblly give me a quick part list?
Thanks a lot,
Michael

 

[audioguru2]

Hi Michael,
I thought this is your project, not mine. I will help you if you run into problems.
1) Design a lowpass filter.
2) Design a peak detector circuit so that the LEDs light long enough to be seen.
3) Design an LED driver circuit.
4) Find suitable parts then make a parts list.
5) Design and make a crcuit board.
6) Assemble and test the thing.

You might want to make an automatic gain circuit so that you don't need to manually match the gain of the circuit to the volume of the sound.

 

[Edude03]

Thanks Audioguru,
Heh, I didn't actually mean a part list, I meant a checklist of things I need to do,
Which is exactly want you gave me.
Thanks,
Michael