Hi, I'm looking for a little bit of guidance here. I'm trying to build a circuit that will take audio input from an electet microphone and light up LEDs to a bass beat. The thing is though, I dont just want them to light up, I want them to fade in and out, glowing brightly when its loud, not at all when there is no noise, and glowing at an appropriate level everywhere in between. So I need to know what will be required to get this working.

My idea right now is to use a comparator fed into a transistor to light the leds. I'll send a sawtooth or flat line into one input, and the audio signal into the other, varying the duty cycle, thus shining the led dimly or brightly. With all of the right preparations (amplifier, low pass filter, etc), will this work? What else will I need to do?

Also, I really have no idea about how to build an automatic level control, which I figure will be a necessity if I don't want to be constantly fiddling with a control knob. Can anyone point me in the right direction for that as well?

 

My idea right now is to use a comparator fed into a transistor to light the leds. I'll send a sawtooth or flat line into one input, and the audio signal into the other, varying the duty cycle, thus shining the led dimly or brightly. With all of the right preparations (amplifier, low pass filter, etc), will this work? What else will I need to do?

I'd go with the sawtooth, at around 10x or more of the highest bass frequency. I'd run the bass through a full-wave precision rectifier before i/p to the comparator. (http://sound.westhost.com/appnotes/an001.htm for an example.)

 

Thank you. I did incorporate the full wave rectification in the circuit. I do have something working now, although it's not perfect. . Once i have time to draw out the circuit I'll post it (BTW, is there any software out there that would make that job easier?). In the meantime... the LEDs still seem "blinky", which i suspect is because there are some very low frequency waves reaching the circuit, making the PWM actually visible. I believe that smoothing the audio input wave would fix that problem, but I'm not sure how to do it.

http://sound.westhost.com/appnotes/an001.htm

I used the last circuit from that link to do the full wave recification. Is there a way to smooth that using a capacitor like you can with bridge rectification? It obviously doesn't have to be perfect for this application, but I think anything would help.

 

Once i have time to draw out the circuit I'll post it (BTW, is there any software out there that would make that job easier?)

if u r talking abt sketching the ckt
circuit maker
http://babbage.cs.qc.edu/courses/cs343/Circuit_Maker/circuitmaker_student.exe
there might be others as well.

 

if u r talking abt sketching the ckt
circuit maker
http://babbage.cs.qc.edu/courses/cs343/Circuit_Maker/circuitmaker_student.exe
there might be others as well.

Thank you! That was exactly what I was looking for.

http://img.photobucket.com/albums/v347/jurgamund/circuit.jpg

This is my current schematic. As I'm typing this I realize I forgot to add in two capacitors that go from +12V to ground. One is electrolytic, 100uF and the other is non-polar, 10n. I'm not even sure what these do, but they were included in the schematic I based the sawtooth circuit off of.

The issues I still have:
1. Any way to smooth the rectified audio wave?
2. It seems like there is a capacitor somewhere that is firing when it shouldn't be. The LEDs will occasionally blink at full strength briefly for no reason after a few hard bass hits. Any idea where this might be originating from?
3. The final design is not going to light blue LEDS like this one, but about 80 red ones. I know how to wire up LEDs just fine, I've done this many before, but I don't think my transistor will handle that too well, as about 320 mA should be flowing through it. Any recommendations on replacements?
4. In case you can't tell, I don't really know what I'm doing all that well. I kind of took a jigsaw approach to this, and I'm kind of surprised I have it working as well as it does. If you see anything in my circuit that I'm doing terribly wrong, please tell me

Thank you

 

1. Try a 0.68uF cap from U4 o/p to ground. (0.68uF might be too big, but its a start.)

2. Golly. No clue here.

3. I humbly suggest ye olde 2N2222a

4. You might have a look at the relevant sections of http://www.allaboutcircuits.com/ to better understand the building-blocks you are using. Fair warning: the more you learn about your components and your basic circuits, the more fun ideas you will have.

 

Haha, yes unfortunately I've been getting tons of fun ideas and the last two weeks have been dedicated to learning and messing with this stuff.

Here's an idea I had... I think the whole thing would look better if the leds were by default glowing a tiny bit, so the that when a big bass hit occurs it isn't so harsh on the eyes. The only way I can think of to do this is to have the audio wave automatically start out at a volt or so. I tried divided the voltage and sending about 1 volt into the plus input of U3a, and then I tried the same thing at the U2B plus input along with the audio signal, but neither of these things worked. Is there a way to do this?

http://img.photobucket.com/albums/v3...nd/circuit.jpg

 

For the mic circuit AGC, I would use the Analog Devices SSM2166 (see attached circuit 1, the mic attaches between R11 and GND). If you pull pin-2 (VGA) low thru ~200 ohms with a properly connected xstr or FET, you can mute/unmute the AGC amp with a control signal (otherwise just set VGA per schematic).

I think you may be better served by the second circuit shown in the attached for buffer/rectifier/filter. On AGC output, change C35 from 0.47uF to 0.22uF. You can add a 100K to 1Meg in series with the input U1 pin-10, after C35, to reduce sensitivity (if need be).

This is a single-ended application where +VAREF is equal to Vcc/2 (third circuit) and will be okay with your +12V (but, you will need to regulate your +12V down to +5V for the AGC amp, a 78L05 or similar should work fine).

So ...you would simply feed circuit 1 into circuit 2, which would then connect into U2B(+) on your circuit, and replace what you presently have going into U2B(+).

 

....

Here's an idea I had... I think the whole thing would look better if the leds were by default glowing a tiny bit, so the that when a big bass hit occurs it isn't so harsh on the eyes. The only way I can think of to do this is to have the audio wave automatically start out at a volt or so. ...

Here is a possible solution for biasing your LEDs on slightly. You will need to experiment with the value of resistance to obtain the level of brightness that suits your eye.

hgmjr