Sound reactive led

[Earl Talatala]

This is my project that I've been doing for a while now. LED will react to music as you play it. I'm a newbie and here's my question. When you connect the LED's ground on the transistor's collector, where should I put the +Ve of the LED? Should I connect it directly on the 12V source? Thank you so much

 

PS: Photo is not mine just found it on google

[Pesukarhu]

Yes, you connect the ground of leds to the collector and the V+ of the leds to the 12v source. If you are using bare leds dont forget to current limit them!

[unknownmiscreant]

Don't do that, put a 300(ish)ohm resistor in series with the led to limit the current, and connect that to the 12v rail. Otherwise your led will be a puff of smoke.

 

Also check out the LM3915 chips. They can drive 10 leds in the kind of thing you are trying to do.

[Unimportant]

1 hour ago, Earl Talatala said:

This is my project that I've been doing for a while now. LED will react to music as you play it. I'm a newbie and here's my question. When you connect the LED's ground on the transistor's collector, where should I put the +Ve of the LED? Should I connect it directly on the 12V source? Thank you so much

 

PS: Photo is not mine just found it on google

Weird circuit. No input protection (and thus, audio source output protection). I'd capacitively couple the input. That would prevent any DC from getting in (or, more importantly, out of) your circuit.

Also, if the audio input is referenced to ground (which it probably is) then it's possible the negative side of the audio waveform will put a negative voltage on the input of at least the top op-amp (which is bad, datasheet says -0.3V max, line audio is typically more). It depends on the source output impedance and how it interacts with that 5.1K resistor to virtual ground.

In the datasheet it says the device can typically source 40mA. At 12V, the 100 ohm base resistor to that transistor will possibly allow (depending on input signal and amplification factor) approximately 120mA to flow, overloading the op-amp.

 

I also don't see the point in using 2 opamps. It looks like the designer wanted to catch both the positive and negative side of the audio waveform to drive the LED. That's probably pointless as audio oscillates so rapidly one side of the waveform would do.

 

This circuit looks to be a much better design :http://makezine.com/wp-content/uploads/make-images/T1yLJy4ftZgGTRxm.jpg

Just remove the microphone and the 10K resistor connected to the microphone and connect your audio input to the left side of the capacitor where the microphone is connected now and you should be good to go. The scematic says 9V but it'll work fine on 12V as well.

That circuit capacitively couples the input trough a 1uF/2.2K (-3db @ 72hz) high pass input RC filter, preventing DC from getting in (or out) the circuit. The first op-amp amplifies the signal while adding a 1/2 Vcc DC bias. The second opamp is then used as a comparator to drive the LED's. It automatically limits the current trough the LED's by using the voltage at the 100ohm current shunt as negative comparator input.

[Earl Talatala]

22 hours ago, Pesukarhu said:

Yes, you connect the ground of leds to the collector and the V+ of the leds to the 12v source. If you are using bare leds dont forget to current limit them!

If I use an LED strip can I directly connect it to the +12V? Thank you for the response btw

[Earl Talatala]

22 hours ago, unknownmiscreant said:

Don't do that, put a 300(ish)ohm resistor in series with the led to limit the current, and connect that to the 12v rail. Otherwise your led will be a puff of smoke.

 

Also check out the LM3915 chips. They can drive 10 leds in the kind of thing you are trying to do.

Will try the LM3915 that you said. Btw, what's the math behind the 300-ish resistor? Why did you come up with that resistor and why do i need it? Tha ks for the response. I'm a newbie so I appreciate it very much.

[Earl Talatala]

21 hours ago, Unimportant said:

Weird circuit. No input protection (and thus, audio source output protection). I'd capacitively couple the input. That would prevent any DC from getting in (or, more importantly, out of) your circuit.

Also, if the audio input is referenced to ground (which it probably is) then it's possible the negative side of the audio waveform will put a negative voltage on the input of at least the top op-amp (which is bad, datasheet says -0.3V max, line audio is typically more). It depends on the source output impedance and how it interacts with that 5.1K resistor to virtual ground.

In the datasheet it says the device can typically source 40mA. At 12V, the 100 ohm base resistor to that transistor will possibly allow (depending on input signal and amplification factor) approximately 120mA to flow, overloading the op-amp.

 

I also don't see the point in using 2 opamps. It looks like the designer wanted to catch both the positive and negative side of the audio waveform to drive the LED. That's probably pointless as audio oscillates so rapidly one side of the waveform would do.

 

This circuit looks to be a much better design :http://makezine.com/wp-content/uploads/make-images/T1yLJy4ftZgGTRxm.jpg

Just remove the microphone and the 10K resistor connected to the microphone and connect your audio input to the left side of the capacitor where the microphone is connected now and you should be good to go. The scematic says 9V but it'll work fine on 12V as well.

That circuit capacitively couples the input trough a 1uF/2.2K (-3db @ 72hz) high pass input RC filter, preventing DC from getting in (or out) the circuit. The first op-amp amplifies the signal while adding a 1/2 Vcc DC bias. The second opamp is then used as a comparator to drive the LED's. It automatically limits the current trough the LED's by using the voltage at the 100ohm current shunt as negative comparator input.

Wow never thought someone would reply this long for the project. Thank you! Btw, like I said, I'm a newbie. Maybe this link will answer most of your questions as I got this project idea from this site.

 

http://www.instructables.com/id/Sound-Reactive-LEDs-1/
 

[unknownmiscreant]

26 minutes ago, Earl Talatala said:

Will try the LM3915 that you said. Btw, what's the math behind the 300-ish resistor? Why did you come up with that resistor and why do i need it? Tha ks for the response. I'm a newbie so I appreciate it very much.

Ohms law. voltage = current * resistance.

This can be rearranged to resistance = Voltage/current.

 

The current for an LED is usually 20mA (0.02A, you need to use amps with ohms law to get accurate calculations). The voltage is the supply voltage (12v) minus the led voltage (3v). 12-3 = 9v.

 

9/0.02 = 450ohms. This is the ideal value. I just guessed somewhere around 300ohms would be suitable for what you were trying to achieve. Although thinking about it, 330ohms is commonly used with 9v batteries, not 12v. My mistake, sorry.

 

Find something between 400-500ohms and it will be sweet. Even 300ohms shouldn't break anything.

 

Maybe wait to try the LM3915, as its a bit more complicated than the circuits you are currently using. Although let me know if you want a hand sorting something out with it later down the line.