Audio meter with 1 watt Luxeons

[ck1]

Hi Everybody,
I am a newbie here.  I am looking to make a "giant" VU meter.  I took a piece of PVC pipe 3" in diameter and 5 feet tall.  I cross-drilled 2" PVC and mounted a 1 watt Luxeon star in the bottom of each tube.  Audioguru's sound level meter is exactly what I want, with the microphone input so I don't have to plug it into my stereo.  It does not have to be accurate, I just want it to "dance" to the beat.  I have attached a picture with the LEDs just hooked to a power supply.

What I need now is to adapt Audioguru's circuit to power the large LEDs.  They run on 3.84 volts at 350mA.  Since the LM3915 has regulated current output for LEDs, I assume I can hook a transistor (PNP I think?) up in place of the LEDs, which will switch the big LEDs on and off.  Can someone give me advice on this?  Be very specific, I am an electronics novice.

Thanks
CK1

[audioguru]

Hi CK,
Welcome to our forum. ;D
You will need a power supply cabable of supplying 3.5A for your project. I haven't seen a 9V supply with such a high current so you can make one yourself from a 12V cener-tapped 5A transformer, a 10A pair of rectifiers and a 4700uF filter capacitor.

PNP transistors like a 2N4403 can drive your LEDs through a 12 ohm 2W current limiting resistor.. The resistors will get hot and need some air circulation because they will dissipate about 1.3W each.

[windoze killa]

Depending on you power supply and how you wire them PNP will be the wrong type. In a "normal" switch configuration the middle letter of PNP or NPN denotes the polarity of the required power supply. As such a PNP transistor will require a negative voltage on the bae WRT the emitter to switch the transistor on. If you can provide a circuit of how yopu intend to hook it up it would help.

[audioguru]

Connect a PNP 2N4403 transistor to the LM3915 and current limiting resistor and Luxeon LED like this:

[windoze killa]

Exactly what I was trying to say. Well done. That should get him out of the problem.

[ck1]

Thank you very much, I will give it a shot.

[ck1]

AG,
I notice you show a 7.8V supply.  I neglected to mention that I have a 5V supply I found on Ebay, will that work?  How does that change the resistor values?
Thanks
CK

[audioguru]

Hi CK,
I planned using a center-tapped 12V transformer to make 7.8VDC. It doesn't need to be regulated.

A 5V supply voltage is too low. There will be hardly any voltage across very low-value current-limiting resistors to allow for differences in the LEDs' voltage and resistor tolerance.