LED Light Box Troubleshoot

[Desirae]

Ok, so I'm working on a sound reactive light box and I am having an issue. When I connect the negative light wire to either side pin on the TIP31, I get constant light, but nothing when it's attached to the center pin. I thought maybe it was a bad transistor, but I switched it out with the same results. There is something I am missing... Any ideas?

 

[KJ6EAD]

Where did you get this circuit design? What is the theory of operation?

 

[CDRIVE]

What is the current requirements for that LED strip? Does it have a built in limiting resistor?
The TIP31 seems like a lot of overkill to light LEDs unless they are high power. The TIP31 requires a lot of base drive to saturate it as the hFE is only 50 MAX and typically only 35. If this LED strip pulls under 100mA you'd be far better off with a 2N2222. They have an hFE>=235. The base should have a limiting resistor too and you should insure that the audio signal does not exceed -5V.

 

[Desirae]

What is the current requirements for that LED strip? Does it have a built in limiting resistor?

12v and yes

It lights up when the neg wire is on either side pin. Solid and bright, but is not sound reactive. The center pin produces nothing

 

[Desirae]

Instructables.

http://www.instructables.com/id/Music-LED-Light-Box/step6/Building-the-circuit/

Mine is a similar one, I replaced a string of LEDs with the light strip. The idea is that when it's plugged into an audio source the LEDs will react to the audio input.

 

[KJ6EAD]

I'd advise you to use a real sound to light circuit design and stay far away from "destructables". You're risking serious damage to your stereo, MP3 player or whatever you're using to light up a few LEDs.

I see the writer of that destructable hasn't responded to you or anyone else having difficulty with that "circuit".

 

[BobK]

What is the source of the sound? Perhaps the voltage is not high enough. It needs to be about 1V.

Bob

 

[Desirae]

The audio source right now is my netbook, but ideally I'll hook it up to an ipod

 

[CDRIVE]

What is the current requirements for that LED strip? Does it have a built in limiting resistor?

12v and yes

It lights up when the neg wire is on either side pin. Solid and bright, but is not sound reactive. The center pin produces nothing

12V is not a current requirment. Do we assume these are a string of common 20mA LEDs?

 

[CDRIVE]

I'd advise you to use a real sound to light circuit design and stay far away from "destructables". You're risking serious damage to your stereo, MP3 player or whatever you're using to light up a few LEDs.

I see the writer of that destructable hasn't responded to you or anyone else having difficulty with that "circuit".

That's because the Internet is rife with bad designs, that are designed by people that know about as much as the people building their stuff.

 

[Desirae]

That's because the Internet is rife with bad designs, that are designed by people that know about as much as the people building their stuff.

KJ6EAD- do you have a rec on a better design that is beginner/intermediate?

 

[Desirae]

12V is not a current requirment. Do we assume these are a string of common 20mA LEDs?

Oops. Sorry. 60mA per segment. Thinking 5 or 6 segments total

 

[CDRIVE]

Oops. Sorry. 60mA per segment. Thinking 5 or 6 segments total

Are you saying that you're going to parallel 5 or 6 of these LED strips?

 

[Desirae]

They're already together, the strip can be cut at the end of any segment

http://www.superbrightleds.com/cgi-...gory=BARS&Page2Disp=/specs/SE-WFLS.htm#photos

 

[CDRIVE]

Are you saying that you're going to parallel 5 or 6 of these LED strips?

They're already together, the strip can be cut at the end of any segment

http://www.superbrightleds.com/cgi-...gory=BARS&Page2Disp=/specs/SE-WFLS.htm#photos

"What we have heeah is a failya to communicate!!" Quote: Struther Martin

I didn't ask you about the series string. Read my question again. Also, I asked you if this LED strip had a built in (integral) limiting resistor. You said yes but I don't think so because the value of the resistor is dependent on the supply voltage and the number of series LEDs, so it can't be fixed internally

Speaking of which, your first schematic shows 7 LEDs in the strip. That won't work with a 12V supply!

 

[Desirae]

Aaah! I'm sorry. Bear with me, I'm new at this.
No just one long strip. I wasn't counting the LEDs in the drawing, there are 15, so 5 segments in all.The packaging says "built-in current limiting resistor, which protects the LED from reversed polarity" so I assumed the answer was yes.

 

[KJ6EAD]

KJ6EAD- do you have a rec on a better design that is beginner/intermediate?

Velleman MK186.

http://www.vellemanusa.com/products/view/?id=525680

 

[CDRIVE]

Aaah! I'm sorry. Bear with me, I'm new at this.
No just one long strip. I wasn't counting the LEDs in the drawing, there are 15, so 5 segments in all.The packaging says "built-in current limiting resistor, which protects the LED from reversed polarity" so I assumed the answer was yes.

OK, I read the sales data the link you posted. They say that their led strips can be cut at every 3 led cut point which they say is about 1" segments. If they're 3 led segments I think the circuit would look like this, which is a series parallel circuit. If anyone is familiar with these strips and thinks I'm mistaken please speak up.

 

[Desirae]

Velleman MK103 with 2 blue LEDs in place of the 4 red ones or connect it to a 12V supply and replace the LEDs with a MOSFET to drive your strips.

http://www.vellemanusa.com/products/view/?id=350678

Sorry, to clarify, you mean replace the LEDs on the MK103 with a MOSFET and connect the strip via the transistor?
Can I connect the MK103 to a 12v supply?

 

[KJ6EAD]

Sorry, to clarify, you mean replace the LEDs on the MK103 with a MOSFET and connect the strip via the transistor?
Can I connect the MK103 to a 12v supply?

Don't bother. Use the MK186. See my edited post above.