opamp driving a led

[thomas2]

hi again.. time for a silly question!
i need to get a led to blink when signal is introduced to input (like guitar for example)..  i know this is easy for you guys, but i didn't get it to work..
so.. i have a couple of ua741 opamps ready. it would be nice if someone would post a schematic or something  :lol:

[gez]

i need to get a led to blink when signal is introduced to input (like guitar for example)..

What's the circuit and why do you need to do this?

[thomas2]

there's many different projects where i could use it.. like for controlling my optical thereminfor example.. with some other instrument.. like guitar..

[gez]

Read Mark Hammer's article on Envelope Filters/Auto-wahs, it'll give you some ideas  

http://hammer.ampage.org/

(a few pages in)

[thomas2]

nah.. too complicated for my english.. :shock:

[petemoore]

I built a distortion clipper {OA} that lit the clipping LED.
 I don't know or can't remember what the circuit was,
 Does this theory make sense:[?]
 Gain up the guitar signal enough, run that signal through an LED to ground and the LED will light when input amplitude reaches a certain level.

[gez]

nah.. too complicated for my english.. :shock:

You basically want an envelope follower.  Have a look at some Envelope Filter/Compressor circuit schematics (ones that use LDR/LED combos).

[petemoore]

Nurse Quacky would be a good one to look at.
 Build the whole thing, get a LED that goes on when input signal triggers it [adjustable], and have an envelope filter to play too!
 IF you're interestied, the post the schematic so we can look at it, it should be fairly easy for someone to cut to the chase of what section of it would light the LED upon command'.
 For my use, would a buffer help keep the 'side chain' [circuit that reads and lights/turns off the LED] from drawing a noticable load from the input signal?

[thomas2]

hi.. i'm currently working on anderton bi-filter using led's and ldr's.. i just want a simple schem for a 741 circuit driving the led.. so i can experiment with some leftover ldr's etc... i don't wanna build the nurse quacky.. i tried it once, worked really hard.. did it work? did it fu%¤"%¤...  :twisted:

[Nasse]

You should look for op amp comparator circuits if you want to blink a led with opamp at certain level. But dunno if 741 is easiest one if you have single supply. Lots of these circuits at circuit sites I quess, look for VU meters and such. But perhaps you want to "stretch the pulse" for short pulse so that sharp and short transients are more visible, which means more components and additional circuitry...

[Ansil]

craig anderton showed us how to do it in the compressor section of the book.. using a dual opamp and a single uncompensated amp he built a simple amplifier with the ldr in the feedback loop of the dual opamp had this signal feed the second half of the dual opamp for the audio section and also had it on a pot ot 10k i belive to drive the input of the uncompensated opamp.  this worked and works just fine.

hope that helps.

[thomas2]

don't have the book.. don't know shit about electronics either.. too bad..
i guess nobody has a simple schematic for this..  :roll:

[Ansil]

i could draw you one based around it but i am at the library currently so i cant' post it even if i drew it.  i could go to the shop and draw it and come back later and post it for you. i fyou want me too.. i will do that. but it would be several hours possibly tomorrow before i got it up.

[thomas2]

that would be super nice if you find the energy to do so.  :lol:
you don't have to if it's too much trouble.

[Ansil]

i will see if i can dig it up and scratch it out and remmber to bring a floppy disk to the library tomorrow.

[petemoore]

Signal indicators and flashing lights are both cool!!! I think I might also like some...YUMMI

[Ansil]

this is similar in theory to the book however i like the lm386 so i built this and tested it out.  fairly accurate reading from soft playing to hard playing.

i used a 5mm green led.  i did not however hook it up to an ldr to see how much resistance it changed as i am currently out of ldr's   anyone have a suggestion on where to get some good ones. i checked mouser but they screwed up so bad recently i dont' htink i wil order from them anymore.

pin 5 is output pin 1 and eight are where the pot connects too.

[thomas2]

thank you sir!
:lol:

[petemoore]

But where do you tap for the signal input?
 Right off the input of the effect? Would this not load the signal...any problems with noise or signal loss?

[Jason Stout]

Ansil, jameco.com has the best selection I know of.