A few quick questions

[Joshie75]

I've been looking for help with this everywherreeee; I need help!
Here's a look at my circuit, which will make 36 ultra bright blue LED's (6000mcd) flash to music playing.



Two main questions;
1)What heatsink do I need for my TDA2050? I have never worked with heatsinks before, and I know nothing about them, I know I sound greedy but could someone link me to the one I need?
2)Where do I connect the positive end of the LEDs (the one labeled (+) after the LED's) The - just goes to ground, correct?

Thank you soo much in advanced; I'm so stressed :-(

 

[(*steve*)]

The points you have labelled + and - do not connect anywhere. They're already connected.

I'm presuming the circuit works. The +12V and ground connections are marked. Connect all the +12V's together (2 of them) and connect them to the +ve side of your battery(?). Connect all the grounds (7 of them) together and connect them to the -ve side of the battery.

Do you need a heatsink, dunno. What package is the TDA2050 in? What current ar ethe LEDs running at? (I guess about 2mA each -- and that's really low -- so a total load of 24mA) You probably want to reduce the value of those resistors.

 

[duke37]

A tip on drawing diagrams.

In your diagram, some wires cross without connecting and some cross with a connection. It must be made clear which is which.

The convention is that the wires are not connected if they just cross over.

To make a connection, you can put a blob on the connection or use two Ts instead of a cross.

 

[Joshie75]

The points you have labelled + and - do not connect anywhere. They're already connected.

What current ar ethe LEDs running at? (I guess about 2mA each -- and that's really low -- so a total load of 24mA) You probably want to reduce the value of those resistors.

The LED's are running at 25mA. They are rated for 30mA max continuous current, and 75mA max peak current.

Thank you for the +/- wire comment, I was being stupid I guess :s

 

[(*steve*)]

If they're blue LEDs, then their Vf is around 3.4V.

So three in series gives you 10.2V.

That leaves 1.8V across 100 ohms, or 12mA per LED (I miscalculated earlier)

Or do they have a lower Vf?

 

[Joshie75]

If they're blue LEDs, then their Vf is around 3.4V.

So three in series gives you 10.2V.

That leaves 1.8V across 100 ohms, or 12mA per LED (I miscalculated earlier)

Or do they have a lower Vf?

We'll the manufacturer I'm buying them from sates the have Vf of ~3.3v
so 2.1V across a 100ohm ohm resistor.

So each LED will be seeing ~21mA. Remember, the max continuous voltage is 30mA, So I didn't want to drop down to the next smallest resistor, just to be safe. After all, with 36 bright blue led's, in a dark-ish room, it won't matter too much.

 

[(*steve*)]

Yeah, that's a problem when the voltage across the resistor is so low. Small variations in voltage can have a large impact on the current through the LED.

You may like to consider how close that op amp can swing to the +ve rail.

This is a power amplifier, not an op-amp, so the specs don't give figures for the output voltage swing. But looking at the schematic, I'd be surprised if it can swing closer than maybe a volt of the supply rails. Thus, the voltage across the resistors may be as low as 1.1V

 

[Joshie75]

@Steve;

What If I try the circuit as is; if the led's are hardly lighting up, they're most likely getting the ~1v you're saying. If this happens, I have PLENTY of 47ohm resistors, which will work nicely,

~1.1/47 = 23ma

By the way; for my audio in, for the 3.5mm audio jack... Do I want to connect the L and R and run them together?

 

[(*steve*)]

try reducing the resistors. You may need to reduce the number of LEDs in a string or increase the supply voltage.

It's best not to simply tie the two channels together. The simple way is to connect the grounds together (they may already be common) then connect a pair of resistors in series between the two signal connections. Take your input from the junction of the resistors. The 47 ohm resistors should be fine for this.

 

[Joshie75]

@Steve;

I don't want to sound or come off rude or anything; why can't you just tie the two together? What does the resistor do, and why a pair of them? Just want to understand everything I'm doing, I'm an electronic hobbiest in the making

I want to thank you so much for your help already and you have been replying to my posts very quickly and you have been so helpful!

 

[(*steve*)]

Tying the outputs together is essentially shorting them together. It probably won't destroy them, but it could.

the two resistors limit the current that can potentially flow and acts to sum the voltages present.

 

[Joshie75]

Tying the outputs together is essentially shorting them together. It probably won't destroy them, but it could.

the two resistors limit the current that can potentially flow and acts to sum the voltages present.

Oh I understand. So the two 47 ohm resistors in serious (94ohms) connect L and R. and in the middle of the resistors is where I grab the input?

 

[(*steve*)]

Yeah, that's right.

Google "summing amplifier" -- the important thing is the input resistors.

 

[Joshie75]

12V DC power adapter ground

I'm using a 120V AC to 12V DC power converted I scavenged off of an old router. So now that I have the 12V DC I need for my project;
Now what about ground?

Can I use the wire with "-" signs all over it as a ground for all the pieces in my project or?

Here's my circuit.

 

[Rleo6965]

The question is. Can your 12V DC adapter can handle required current of your circuit?

 

[(*steve*)]

And also the other three that Rleo missed (under C3, C5, and the op-amp)

 

[Joshie75]

Thanks Rleo,

I tested the adapter with my multimeter;
I secured the wire with the -'s on it to the black tester, and the other wire was secured to the red tester. I got -12v DC. So does this mean the side with the -'s down it is actually positive? Don't want to ruin any components do to backwards voltage or anything.Thanks;
Josh

 

[Rleo6965]

So does this mean the side with the -'s down it is actually positive? Don't want to ruin any components do to backwards voltage or anything.Thanks

Your multimeter will confirm the right polarity of dc voltage. You can also look at label or sticker of your DC adapter that show a drawing of wire connector with corresponding polarity.

 

[Joshie75]

So I took all your guys' advice, re soldered my power adapter; and my LED's light up, yay! Man are they bright. Though when I plug my phone to the audio in, the LED's aren't flashing/flickering; any ideas? :\

EDIT; changed are to aren't above. sorry.

 

[davenn]

So I took all your guys' advice, re soldered my power adapter; and my LED's light up, yay! Man are they bright. Though when I plug my phone to the audio in, the LED's aren't flashing/flickering; any ideas? :\

EDIT; changed are to aren't above. sorry.

Did you read and do what steve said re the other points in the cct to be connected to
the negative of the power supply ?
If you missed particularly the pin 3 of the IC then the IC wont be working and the lights wont flicker.
I would have half suspected that, with no input audio signal, the LED's would be lit and would only start to light up as signal is applied. And following on from that though, ensure your input signal isnt too higher level else you will be in a permanent overdriven state

Dave