Listening to an LED...

[SolderBoy]

Hi there! - this is my first posting - so be gentle with me!  :wink:   Great forum, by the way - I've been lurking for a few months...

A weird sounding question, but please bear with me...

I have a loop sampler pedal that has a blinking two-colour LED (which indicates the tempo as a guide - red on 1, then green on 2-3-4).  I'd like to be able to turn the blinks into a click track.  There is just room for an extra jack, so I thought I'd run the leads from the LED to a jack and have the click track circuit in a separate box.  I was thinking that an opto-coupler or two would be good for triggering the clicks - that way the pedal's existing LED circuit is not really effected too much (if you know what I mean).

Can anyone suggest a circuit that will do this.  IE: take the current pulses from the dual-LED, couple/isolate them and make a two-tone metronome type "tick-tock" sound to drive a pair of headphones, plus light another pair of nice bright LEDs.  (The existing two-colour one is not very bright.)  

My approach so far has been to play around with a few of the millions of simple metronome circuits that are around the web.  I was thinking that I could make two and simply filter one of them for the lower pitched "tock" sound.

I hope this all makes sense.  Its really a very simple idea - its just my attempt to describe it that makes it sound so complex!

cheers.

PS: The next step is the complex one - I'd like to also have the click create a midi signal - imagine having Ableton Live sync to your sampler pedal - very cool!  ...but first things first...  

[bwanasonic]

It might be usefull to specify which loop sampler pedal you have. Is this a DIY or commercial effect?

Kerry M

[Paul Perry (Frostwave)]

One side of the blinking led probably goes to earth.
Hook a 0.1 mfd cap to the other side, and run it into an amplifying circuit.
Then you have your click!!! (try filtering with cap & resistor to get the click to sound how you want).

[SolderBoy]

Hi Guys, sorry about the slow response - busy week.

The loop sampler is a Boss RC-20.  It has a click track already, but it comes out the main output - making it useless for live sampling.     I think the click comes straight off the same digital chip as the samples etc. and the volume control for it is not part of an analogue mixer arrangment, but is a control voltage for a DSP type mixer.  (I've tried "listening" to this control pot!)

So, thinking outside the box, I thought I could more easily "listen" to the blinking LED.

The common cathode of the green/red LED is not connected to earth - that's why I thought it would be best to use the opto-couplers.   I've listened to the pulses as Paul suggested.  They are short notes, ("E's" actually - 165 Hz), and sound like a square wave.

So how do I turn these into a percussive "click" - like a metronome.  Buffering, filtering, and amplifying them after this shouldn't be a problem.


Cheers.

[zachary vex]

find the circuit for a side-stick sound (twin-t filter) used in lowrey genie organs or some such old-school drum machine.  those self-oscillating filters are easily built and can be easily tuned to slightly different pitches (tick and tock) and it's easy to make them decay just right by reducing the gain on the transistor by increasing the emitter resistor.  they can also be easily triggered by touching one of several points in the circuit with your finger, so it should be easy enough to put a cap in there to the LEDs to trigger the thing.

on edit:

i snapped a picture of part of an old drum machine schematic from a popular electronics article (childhood memory, heh) to show you how easy this is.  take a peek:



the transistors are specified as 2N2712, but you can sub 2N3904.  the top line is +V (sub a 10uF for that cap on the far right), the bottom line is an audio output bus (wire that to your amplifying stage somehow), and points L and M are the trigger inputs.  you might have to futz with a few of the resistor and cap values (like around L and M) but it will probably work to simply connect whatever is driving the two LEDs to those two points.  parts values aren't incredibly critical... feel free to sub some and goof  around with it.  it should oscillate with a variety of parts substitutions that are reasonable.  the pots are to adjust the pitch of the two drum noises (tick is the clave, tock is the wood block).  have a blast!  8^)

[toneman]

Ahhh,the Old "DrummerBoy" by PAIA....
memories...........................................
How can U hear a "click track" on stage??
Oh, U want a "click track" for recording.....(?)
the red/green LED has 3leads.
tap of the signal leads(2) as Paul suggested.
will have narrow spike.
buffer spikes, then run thru pulse stretcher.
mix 2 stretched pulses so U can tell "1" from "2 3 4".
run mixed/stretched pulses 2 dedicated click track.
No need for MIDI.  record as wave.
If MIDI absolute, use stretched pulse to trigger a key on extra synth.
This will generate a "MIDI note/click" that U can record.

T

[puretube]

nice: the 1st  thread asking for making the click audible  

[SolderBoy]

Zachery, that looks great, actually I have a few of these type of circuits kicking around myself, now that I think of it...

Toneman,

How can U hear a "click track" on stage??

I wanna send the click to the drummer's cans.  The RC-20 has a tap-tempo footswitch which sets the guide click (and blinking grn/rd led) going.  Stomp the other switch and you are recording, stomp again and it loops your sample (of up to 5mins!) and magically lines it up with the guide click - very cool, and even cooler if you could do it live - on stage.  But when you wind up the RC-20's click track to help out the drummer and rest of the band, the audience will hear it, because it seems the good people over at Roland never thought you'd want to be able to separate it from the sampled material at the main output - frustrating.

No need for MIDI. record as wave.
If MIDI absolute, use stretched pulse to trigger a key on extra synth.
This will generate a "MIDI note/click" that U can record.

The MIDI idea, again, is about on-stage sampling.  Ableton Live is sequencing software that is designed for live remixing etc.  I believe it will sync to midi - via smpt or midi clock, but you can also set just about anything on the screen to be triggered by midi - including its own "Tap" button.  Having the click track in the RC-20 also produce a simple, single midi note, would mean Ableton could be set to chase the RC-20's tempo - again, awesome for live sampling.

[SolderBoy]

This afternoon I finally had a chance to breadboard Zachery's Drum machine oscillator circuit.  This is great.  Just perfect for a click track.

But after messing around for a while, I still can't get it to trigger cleanly from the RC-20.  Problem is, that the "E" tone that I mentioned comes through loud and clear, even though it now has a tick or a tock on the start of it.  I've tried isolating, rectifying, and filtering...

Any ideas...

[zachary vex]

it's Zachary.  8^)

[SolderBoy]

oops, sorry about that.

Speling was nevar my strong poynt.

[SolderBoy]

:oops:  :oops:  :oops:

Oops again!!

Had the rectifying/smoothing stage wrong.  Works great now!  

Can't wait to get this off the breadboard, into a box and off to a gig!


Thanks again guys!

   

[inverseroom]

Somewhat OT, but Zachary, have you ever thought about producing a 1509B-size analog drum machine?  A few projects like that and it would be possible to have a ZVex-only band...