LFO switching led issue....

[deadastronaut]

hi guys i have this lfo , works perfectly...

i added a switch to switch between 2 caps for fast and ultra slow...

however the led is very dim when switched either way...but goes very bright momentarily whilst switching

so i dont want to blow the bugger....

im only getting around 2v at the led when switched....so obviously the the led is struggling, hence the dimming...ive even changed R36 1k to a 100r..and still the same...

is there a better hookup point for the led to pulse...

i dont want to blow the led as i have it glued in place...but i can tap the led resistor to another point

cheer guys...

[Rob Strand]

The issue is probably the low thresholds set by the Schmitt-trigger.  That's going to make the range of voltages at the output of IC4A lower DC wise.  So what about connecting the LED to +V?     You might then need to add some series diodes to tweak the range of brightness.  It will obviously flip the polarity of the LED relative to the LFO.   Other than that you would need to add a transistor or MOSFET to drive the LED.

[deadastronaut]

cheers rob, i'll put the 1k back in and try hooking it up to 9v....whilst connected where it is on the depth  too...

back in a bit. 

[antonis]

Or maybe by lowering R27 Value..
(just a rough thought..) 

[deadastronaut]

well the 9v didnt work......boo hoo...

antonis, hmmmm wouldnt that mess my lfo up?.....

might be worth a go though i guess..

[antonis]

antonis, hmmmm wouldnt that mess my lfo up?.....

As far as it concerns YOUR lfo, frankly, I don't give a damn... 

More seriously now, I believe it will widen Schmitt-trigger threasholds..

[deadastronaut]

   me neither ha ha.....

cool i'll give the 220k  a go then... 

[deadastronaut]

yay top man...100k did it instead of the 220k....

cheers man......

[antonis]

Well done then.. 

P.S.1
In case LED persists to initial switching high brightness, ulitize a "delay" circuit like the one used for 3PDT switches LED anti-popping..

P.S.2
Academical interest: Can't realize the reason for Rob's suggestion not working..

[duck_arse]

hardwire C2 between pins 1 and 2, and then only switch in the 47uF. that might stop the light blast.



antonis the hardman might not care, but we do, Rob.

[deadastronaut]

all sorted now ducky.....you have to get up early

and it didnt turn into a 48 page thread...

[duck_arse]

early? there are some people want me to get up tomorrow instead, just so's I'm on the same day as them.

[anotherjim]

early? there are some people want me to get up tomorrow instead, just so's I'm on the same day as them.

You don't have to get up tomorrow, you can just behave like it is yesterday today until it's the proper time for today to become tomorrow.

[antonis]

hardwire C2 between pins 1 and 2,

And exactly where is presently located C2..??

[Rob Strand]

And exactly where is presently located C2..??

C22.   duck_arse's idea keeps one cap connected to stop the opamp glitch (good idea).

[duck_arse]

.... 2. wait for it, antonis.


is it now, yet?

[antonis]

I've been waiting for more than 24h searching for C2 in Rob's schematic..

[diffeq]

And exactly where is presently located C2..??

C22.   duck_arse's idea keeps one cap connected to stop the opamp glitch (good idea).

With centre-off switch, it even allows for a middle, ultra fast, option.

[duck_arse]

well waiting 24h in one of Rob's threads, about leds no less, instead of 24 pages ..... you should thank me.