opamp driving a led

[thomas2]

just one question about this... what does it mean if the led blinks brightly when the battery is switched on and then blinks a few times when the guitar is being strummed.. after that nothing happens.. when i take the battery off and put it on later.. the same thing happens again  :roll:
















                                                                                               :twisted:

[thomas2]

of course one reason may be the old components i'm using.. i don't have new ones so i just use whatever i find from my old computer, vcr, radio, guitar amp, turntable... i did check the electrolytic cap though.. i even tried three different ones.. so i believe the problem isn't there.. oh yes!! i didn't find the right pot! could i use a 10k for example? :lol:

[petemoore]

Yes, since the pot is used as a V/R, and pins 1 and 8 set gain on 386, a 10k should get you 5k resistance, well above and also below that R value...

[smoguzbenjamin]

You could use the output from ansil's schemmo and attach it to an LED driver. That way you could use 10 LEDs and have one of those cool rising bars as an indicator. When I finally get round to building a guitar amp that will be a feature for sure.

[petemoore]

Thanks Ansil, Probly gonna try that out here in a while.

[petemoore]

Well it lit the LED just Dimly for the first bang on the strings, after that...nothing...[?] I tired upping the 5k [I was stuffing fixed resistors in] all the way to 22k...anyone tried this successfully, maybe you can help me figure out what's up with mine.

[thomas2]

same here! just a few blinks and then nothing  :lol:

[smoguzbenjamin]

My guess is the cap. Since a cap blocks DC by nature it might be doing something funky with the LED. Try removing that and see what happens then.

[petemoore]

My guess is that it's the cap doing that too Ben.
 Because it just seemed like current flowed until something 'filled' then no more lighty...

[smoguzbenjamin]

Did it work without the cap?

[petemoore]

I din't try it..I though You Were...
 I don't know what's going on [or off] with the circuit...so it's on the 'back burner' 'till [and if] something more comes out of it ...information wise.
 U just drove mine straight off a guitar pickup, maybe more juice at the input?...signed: Not too Concerned

[Torchy]

Hacked from the Nurse Quacky for comparison ... may be able to b/board this tonight ..

[smoguzbenjamin]

I might have time this evening to breadboard it out. I just finished up the switching problem with marcos's robovox

[petemoore]

Kool. that fits my bill, because I have a sleugh of 741's...[I wouldn't even spring for a switch for one of these in a signal path]...that I wouldn't know what to do with otherwise
 Looks like any single OA would do the trick there!!!
 Could be used as an indicator I'd think, you'd have to play to see if it's on..or set the detector sensative enough to turn on with background noise...
 Might need adjusted to accomodate various input voltages and still turn on/off...say if you put a big boosty fuzz before it...that's what the 100k's there for...of course you could use a fixed value, set for 'sensative' so it would go on with clean guitar and go on 'hard' with signal boosted.

[thomas2]

ok.. would someone please tell me what's wrong with the 386/led circuit? i tried it without the cap (led turned on when power was connected) and with different value caps (first few blinks were bright and then slowly turned dimmer until there was no light) i tried to replace the pot with fixed resistors.. again nothing happened.. help! :shock:

[petemoore]

I dunno :twisted: I tried it too...
 The 741 thing don't werk with the Green LED, must be different...why it calls for the red ones, which I need to get some of...741 thing has to work if it's right off the NQ...Cause I have a NQ that works and the LED comes on and fades with the attack/sustain.

[thomas2]

well i'm not gonna waste another piece of my valuable perfboard before it's absolutely sure it's gonna work.