LED flasher to music (needs improving... transistor help)

[audioguru]

The transistor buffer that was shown is an emitter-follower that doesn't have any voltage gain. It has voltage across it and current through it and its heating is that voltage times that current.
If you used a current-limiting resistor in series with the LED to protect the LED from burning out, then the transistor did nothing. Connecting the LED and its series resistor at the speaker would have lighted it the same.

How did you connect other LEDs?

Didn't you use a resistor in series with the transistor's base to limit its current?

 

[madmikejt12]

i did that circuit as shown, the LED's are all connected together, there is no current limiting resistors in series with the LED's because there is no current to limit!! lol i didnt have a resistor to the base, but it didnt work without it so it shouldnt work with it should it?

 

[audioguru]

i did that circuit as shown, the LED's are all connected together

The transistor is shown as an emitter follower but you said earlier that you connected LEDs to its collector instead of to its emitter. Why?

You don't say how you connected the LEDs. In series? In parallel?

, there is no current limiting resistors in series with the LED's because there is no current to limit!!

If there is enough voltage in the circuit for the LEDs to function then they or their driver will burn out without having current-limiting resistors for them.

i didnt have a resistor to the base, but it didnt work without it so it shouldnt work with it should it?

The base-emitter junction of a transistor is a diode that always needs a current limiting resistor. If it is connected as an emitter-follower then the emitter resistor limits its base current.

It is very confusing to talk about your circuit without seeing its schematic with a supply voltage and parts values. Please attach its schematic so we can recommend how to fix it.

 

[madmikejt12]

The transistor is shown as an emitter follower but you said earlier that you connected LEDs to its collector instead of to its emitter. Why?

You don't say how you connected the LEDs. In series? In parallel?

the LED's are in parallel

If there is enough voltage in the circuit for the LEDs to function then they or their driver will burn out without having current-limiting resistors for them.

With the resistor there, they don't work at all

The base-emitter junction of a transistor is a diode that always needs a current limiting resistor. If it is connected as an emitter-follower then the emitter resistor limits its base current.

It is very confusing to talk about your circuit without seeing its schematic with a supply voltage and parts values. Please attach its schematic so we can recommend how to fix it.

Here is the diagram: (havnt got schematic for the amp but am trying to get hold of it) **broken link removed**

Thanks,
Mike

 

[audioguru]

the LED's are in parallel

You can't connect LEDs in parallel, their forward voltage requirements are different. They should each have their own current-limiting resistor or be connected in series and in series with a current-limiting resistor.

With the resistor there, they don't work at all

Then the circuit doesn't have enough voltage. The transistor should be used to amplify the voltage, not just follow it.

havnt got schematic for the amp

The amp's schematic is available from the web if you say what it is.

 

[audioguru]

Your little amp is probably designed for an 8 ohm load. If your 4 speakers are each 8 ohms then the four of them in parallel is only 2 ohms, which is like a short to your poor little amp. You are lucky it wasn't destroyed!

I have used the schematic of an LM386 1/4W amp that is designed for a load of 8 ohms. I connected the speakers in series/parallel so they are a 8 ohm load to the amp.
I have connected a transistor with a current-limiting base resistor and a sensitivity control. The transistor amplifies the output of the amp.
I have connected the LEDs in two series strings, with a current-limiting resistor for each string.
With a brand new 9V alkaline battery, the LEDs will glow with a max current of about 24mA. The amp and LEDs are a heavy load for the little 9V battery so its voltage will drop fairly quickly causing the amp to distort and the LEDs to dim. The little battery won't last long.

 

[madmikejt12]

thanks, will try that.. i have a rechargable battery so i dont need to keep buying new ones.

so, up to the 470uf cap is the amp is it? so i just need to add the speakers, led's (& resistors), transistor and the pot?

Thanks, Mike

 

[audioguru]

A little 9V rechargable battery is only 120mA/hrs at only 7.2V, so the circuit will play music and blink the LEDs for only about 4.8 hours.
If it is turned up too loud (from only 1/4W?) so the amp distorts, and the LEDs are on most of the time then the rechargable battery's charge will last only 1 hour.

 

[madmikejt12]

i use the computer's usb aswell sometimes, this works fine, i just connected a pp3 battery clip to the + and - wires, most of the time i use headphones, so i will charge the battery every night and leave it on overnight.

Thanks for the help
i'll let you know how i get on

 

[madmikejt12]

that worked thanks but ive now got another one and wish to insert bulbs into my speakers (behind the cloth so it shines through)

so, i connected the i/p and 1 red LED to the o/p with no current limiting resistor, the mp3 player was on full volume and i only got flashes of realy loud beats (not all songs worked) but when i connect my multimeter (set to diode test) it goed brighter but still flashes to the music, could i just add a battery in parallel to the LED because that is like what the multimeter is doing isnt it?

EDIT: i am not using speakers this time, just the LED's
Thanks,
Mike

 

[audioguru]

Hi Mike,
I do not understand how you wired the LEDs and why you did not use the current limiting resistor and the transistor.
Please sketch how you have it wired.

 

[madmikejt12]

would the transistor crkt work with 2 LED's in series and no speakers without the pot?
i wired like this:
_______
+ l-------l\ l
AMP l l \l___
CKT - l-| l /l l
_______l | l/ l l
| l
|__________l

With multimeter:
____________________
l +multimeter
_______ |
+ l---|---l\ l
AMP l l \l___
CKT - l-| l /l l
_______l | l/ l l
| l____________-multimeter
|__________l


Sorry if its hard to understand, paint isnt working

EDIT sorry, looked different when i was typing it


baisicaly this:

Amp output (+) ---> LED +
Amp output (-) ---->LED -

With multimeter:

Amp output (+) ---> LED + ---->Multimeter +
Amp output (-) ---->LED - ----->Multimeter -

 

[audioguru]

The LM386 amp doesn't have a (-) output so maybe you are using a different amp.

Without a speaker to discharge the 470uF output coupling capacitor, it will become charged and cause the transistor not to work.

 

[madmikejt12]

it may just be the negative terminal of the power supply because there is a 3.5mm jack and then 2 solder pads, one with + and one with -

is there ANY way to have the LED's to flash at a decent brightness without speakers?

can i get rid of the cap and put a jumper wire there?

 

[audioguru]

This circuit will flash its LEDs with the music. It has an extra 10uF cap for more gain. It probably won't work with a supply voltage of only 7.2V from a rechargable or run-down battery.

 

[madmikejt12]

ok, thanks.... i have my new antex soldering iron now so i think i'll give it a go

 

[moody07747]

Ah, i'd definately advise pending some money on one like this:

**broken link removed**

Thats what I use now, looks like its reduced at the moment too

I use this solder with it, it gives good results:

**broken link removed**

]

Yea im saving up for one of those as well....the 110V input version though that

 

[madmikejt12]

i have that one (240v i think) i got it for £9.99 on promo

 

[rstockham]

Questions on blinking lights to music

Audioguru, I've setup your last diagram you posted for Music player's input with the 10uF cap between 1 and 8. I'll admit I'm no expert electronics person. I used to be out of college, but when you don't use it you lose it. The way I have it setup is taking sound out of a laptop and splitting it, one connection to your circuit and the other to speakers. It works fairly well, but the leds are almost always on. I would like it to be more sensitive to the beat of the music and not so much just any sound coming through. What part of the circuit do I need to modify to get closer to this effect?

Also, I'd like to add quite a few more led's than just two. I've read some of the posts, but am still unclear. If I'm using an actual plugged in constant 9v power source (not battery), can I just keep adding multiple parallel sets of led's with a resistor in series with each of them. How would I calculate what kind of resistor I need?

I appreciate all your posts and any help you can give me.

Thanks,
Ryan

 

[madmikejt12]

the 100k pot is used to control the sensitivity, try changing that for a larger value, e.g a 1M