Hi,

Im currently making a light box circuitry project that I need to finish for next Wednesday and I am having a few problems with the design of the circuit. It is required that the light box pulse in time with the music however I am working with a low budget and have relatively low skill level so in that respect simplicity and cost effectiveness is the key.


As an initial basis I was going to use this circuit, http://hacknmod.com/hack/led-light-box-thumps-to-your-music/

although I have a few questions with regards to its functionality. I assume that I will have no problem modifying the circuit for a 12v wall socket set up, and although the LEDS are different to the ones draw I cannot see there being any issues of connectivity of the circuit.

I do however want to change the connection to the Tip 31 transistor to a microphone instead of a phono cable. Will this still work with the tip 31 transistor? I will also require a volume control for the microphone so that I can alter the sensitivity of the pick up dependant on the surrounding volume.

Thanks in advance for your help,

 

There are problems with that circuit. First, you are unlikely to be able to drive 4 blue LEDs in series satisfactorily from a 12V battery/wall-wart, since each LED has a forward voltage of around 3.4V-3.6V. Second, if one LED should fail short-circuit there is no series resistor to limit current and the others could fail. Third, it would not be sensitive enough for a mic input.
How do you plan to connect 5050 LEDs? They will generate a lot of heat.

 

A microphone will not be able to drive your transistor directly - you'll need a pre-amp. The details of that will depend on the type of microphone you're using.

Are you planning on switching ALL the LEDs together? You're getting into serious power. If each LED requires 50mW, then 5050 of them needs 253 watts - over 20A at 12V. The TIP31 cannot handle that. Look for a darlington rated to well over that current. Common TIP122 isn't big enough.

I'd normally say to use a MOSFET for switching that large a current and that might be a good idea, but I'm not sure how the effect might look, compared to a BJT.