Attention EE wiz types - "pong" type LfO sweep mon

[Mark Hammer]

On several occasions recently, the topic of where and when tap tempo was useful came up.  I've mentioned that I found tap tempo to be relatively useless whenever the tempo/sweep-time exceeds an identifiable rhythm tempo.  I don't think I'm alone there.

It occurred to me that some type of visual sequence indicator might assist in planning out one's tapping of the tempo.  I might also note that driving home just now, I heard some nameless tune on the radio where the guitar player was able to start a riff from a certain point in the sweep cycle of a flanger, and I thought it would be useful for some musicians to be able to know when they were at a certain point in the sweep cycle before they started playing.

So here is the deal.  You can buy these LED Meter stacks that pack 10 rectangular LEDs into a compact package.  These are often driven by LM3914-3915-3916 bargraph chips (only one of which is useful for our purposes but I forget which).  What I'm wondering is if it would be relatively feasible to design a "pong" type LFO status display, where the relevant LED would light up as the LFO waveform went high and low.  Certainly for LFO rates that are fast enough, a simple flashing LED is fine, and for things a little longer, maybe a bi-color LED going bip-bop-bip-bop is good.  But once you get out to sweeps that take 5 sec or more, you need something that can tell you "We're almost there" in a visual way.

Since many comparator/integrator type LFOs often have a simple rate monitor in the form of a resistor and LED hanging off one of the outputs, I'm assuming that the same type of LFO could also feed the hypothetical status monitor described.

So, does this sound useful?  
Does it sound feasible from one of those bargraph chips? (that have a bazillion "designing with the LM39xx chip" articles published in every magazine, as well as tons of app-notes from the manufacturer)  
Is there something already like this out there?  
Are 10 stages of display (5 for positive half-cycle, 5 for negative) enough?
Does one absolutely need separate colours for the two half-cycles or some other color scheme, or is one single color enough?
Is this the sort of thing that could simply be added onto any pertinent LFO, or would it be confined to certain working parameters?

[Bill Bergman]

Or have a foot switch that resets a flange cycle or sweep to zero when you want to start a riff.

[bioroids]

I'm starting to design a tremolo in wich the lfo starts when guitar signal is present, and it will start on the full amplitude part of the waveform.

I think this is pretty usefull when you want the effect to be in sync with the band.

In this way, the player tells the effect when to start, instead of having to wait for the effect to be in the "right position" (wich may be imposible on a band situation, unless is the start of the song)

This might apply to other modulation effects; in case of a flanger may be a nice adittion a pot to control where in the cycle it starts once the signal is present, or perhaps a switch to control if it starts going up or down. I dont know how this could be done anyway :oops:

Luck

Miguel

[Processaurus]

I was originally just going to use the LED part of this as a VU meter, which isn't particularly useful, but now I'm thinking it would be good for monitoring an LFO.  



I like what you guys are thinking about in terms of better using slow sweeping modulation stuff in an actual band situation, they are frustrating because you probably want them to sweep at a certain point in a phrase, but they tend to have a mind of their own.  The note triggering stuff would be amazing, (especially for tremolo!) if it could work predictably.  An easier option to implement would be the LED pole of your 3pdt stompswitch could hold the LFO high or low while the effect is bypass (and maybe have another footswitch for whether it was high or low).

[Dave_B]

Or have a foot switch that resets a flange cycle or sweep to zero when you want to start a riff.

Doesn't the PAIA Hyperflange do this?  Of course, that LFO is a >$50 solution...

[Pedal love]

I was originally just going to use the LED part of this as a VU meter, which isn't particularly useful, but now I'm thinking it would be good for monitoring an LFO.  

That is a cool pedal!

[Dave_B]

So here is the deal.  You can buy these LED Meter stacks that pack 10 rectangular LEDs into a compact package.  These are often driven by LM3914-3915-3916 bargraph chips (only one of which is useful for our purposes but I forget which).

I'm pretty sure it's the 3914.  The 3915 (I think) is logrithmic.

What I'm wondering is if it would be relatively feasible to design a "pong" type LFO status display, where the relevant LED would light up as the LFO waveform went high and low.

That would seem to be fairly easy.  For whatever the voltage range for the input of the 3914, you could feed the LFO into an opamp that would condition the voltage.  That's off the top of my head, and I haven't messed with a 3914 for almost 20 years, but I think it wouldn't be much harder than that.  

Certainly for LFO rates that are fast enough, a simple flashing LED is fine, and for things a little longer, maybe a bi-color LED going bip-bop-bip-bop is good.  But once you get out to sweeps that take 5 sec or more, you need something that can tell you "We're almost there" in a visual way.

Um... are you talking about one unit doing all that?  If so, you're out of my league.  

So, does this sound useful?  

I'm not sure what you'd do with it.  Wouldn't that mean the entire band/recording would have to follow the (possibly flakey) LFO?  I miss the point a lot, so maybe that's the case here.

Does it sound feasible from one of those bargraph chips?  Are 10 stages of display (5 for positive half-cycle, 5 for negative) enough?

I think it would work.  If 10 steps isn't enough, I'm almost positive you can cascade those chips.  I can't remember how to do it, but it's in that old yellow Forrest Mims book if you have one.

[Transmogrifox]

I think this is feasible and useful as well.

I would like to see more than 10 LED's just because it would be real cool looking.

For more, say, 20, you can cascade these very easily by going like this:

Vcc-->Rhigh(IC1)
Rlo(IC1)-->Rhigh(IC2)
Rlo(IC2)-->Vee

Instead of using Vcc and Vee for max and min references, you could stick resistors in the high and low reverence to narrow the range to the max and min of your LFO.

IC1 and IC2 denote two separate LM3914 chips.

You could take an extra LED directly out of the LFO in series with a capacitor and resistor.   The capacitor is a high-pass filter that is adjusted to prevent the LED from illuminating at low speeds, but it would blink at higher speeds.  You would  locate this LED right next to the "0" mark on your bar display (or linear array of LEDs) as a 0 marker as well.  

The real trick is to take your basic LFO and make the rate tap adjustable and trigger started from any reference you want.  I think that would most easily be done with a micorcontroller.  Otherwise, you might consider joining the DIY analog synth page for more ambitious projects. :wink:

If I have some time, I can easily work up a schematic for the display part of this that assumes a tap tempo LFO is already in place.

[Transmogrifox]

Datasheet for anyone interested in an easy link:

http://cache.national.com/ds/LM/LM3914.pdf

[Mark Hammer]

Certainly for LFO rates that are fast enough, a simple flashing LED is fine, and for things a little longer, maybe a bi-color LED going bip-bop-bip-bop is good.  But once you get out to sweeps that take 5 sec or more, you need something that can tell you "We're almost there" in a visual way.

Um... are you talking about one unit doing all that?  If so, you're out of my league.  

No you can rest easy. :lol: I was just trying to comment on how some sorts of LFO indicators are perfectly sufficient up to a certain point, after which they just don't seem to give enough information and something else becomes necessary.

What I'm thinking of is a simple add-on for those instances where people need to be able to accurately anticipate the sweep of something that is moving too slow to keep track of in their minds.  With things that modulate/oscillate at a certain rate, it's easy to mentally "sync" with the modulation, and even if it goes dead quiet the person can sync up with it perfectly when it resumes. not unlike a drummer imagining a beat.  Once it gets slow enough, you can't do that...or at least I know *I* can't.

[Dave_B]

With things that modulate/oscillate at a certain rate, it's easy to mentally "sync" with the modulation, and even if it goes dead quiet the person can sync up with it perfectly when it resumes. not unlike a drummer imagining a beat.  Once it gets slow enough, you can't do that...or at least I know *I* can't.

Sort of a stompbox equivalent of this:

[Mark Hammer]

Bingo.

[toneman]

There was/is? a site that has/had a "Knight Rider"  PIC driver.
U remember "Knight Rider"??
Also remember another site for a "Cylon"  PIC driver.

Now, both of these have/are built-in back/forth sequencers.
But, U could use an analog input to the PIC , so that it determined
what voltage the input signal was at.
 Yes, this would have 2 B DC-coupled,
AND would have 2 B no greater than the PIC voltage (5V).
Just scale it down with resistors.
My first PIC project was the Cylon counter.
Of course, yes, the 3914 does this already.
AND they are stackable!!

Presently (only for a year+    I've been "working" on a 10LED
bargraph for one of the phases of my 8-phase ShepardGenerator.
20LEDs would B "better", but U have 2 start somewhere  
It's based on the 3914.
OH, BTW,
A LFO can B given a "hard sync" and it will start "at the beginning".
(there probably would B a "glitch", but if U wern't playing......)

ByYourCommand
StayToned

[petemoore]

Zero Through Flange that goes over the top 1 or few times beginning at the touch of a button !!! Sorry, OT, would be neat trick..Im' sure it *Could be done, not by me this year.. :roll:

[MartyMart]

There's a unit for "drummers" ( I know, I know ! ) I think it's called the
"MIDI Conductor" which takes a MIDI timing connection ( from sequencer or smpte unit) and displays a large row of LED's. ( 19 inch rack )

As the tempo is recieved the LED's "sweep" left to right in much the same fashion as a conductors "baton", far left & far right being the "blip-blip"

I'm told that its much easier to follow the tempo this way "visually"
( though I've yet to hear a drummer who can from ANY source !!! )

Great Idea !!

Marty.

[gez]

There's a unit for "drummers" ( I know, I know ! ) I think it's called the
"MIDI Conductor" which takes a MIDI timing connection ( from sequencer or smpte unit) and displays a large row of LED's. ( 19 inch rack )

As the tempo is recieved the LED's "sweep" left to right in much the same fashion as a conductors "baton", far left & far right being the "blip-blip"

I wonder if it could be hooked up to an LDR, or if the LED controller could be tapped, to create a midi controlled trem.  If you remember its name, please link to it Marty.  

[Dave_B]

I wonder if it could be hooked up to an LDR, or if the LED controller could be tapped, to create a midi controlled trem.  If you remember its name, please link to it Marty. 

A MIDI-controlled trem relates to the PIC LFO I was thinking about the last few days.  There are sites that detail how to read the MIDI data.  If you read just the MIDI clock, you could calculate the tempo and generate a waveform to control the trem.  It could be little more three chips (opto-isolator, a small PIC, DAC) and a few resistors and caps. 

No, I haven't actually done it.   

[soggybag]

That bargraph chip is pretty neat. I saw some interesting use of it over at Grant Richter's site.

That pedal with the LED's is very cool! Do I understand correctly that the lights all light up in sequence based in the input?

[Nasse]

http://diystompboxes.com/smfforum/index.php?topic=37626.0

This kind of lfo has some info available between peaks and valleys, in theory, so could such a generator be the starting point to make something visible at very low speed


Just tried to google about a discontinued (?) commercial device "Russian Dragon" some kind of visual tempo/deviation indicator, I think it was midi thing but found not much info or pictures how the display works, but the name is tweaked form "rushin/draggin"

EDIT I found some interesting pics and text with internet wayback machine http://web.archive.org/web/19970702182615/www.russiandragon.com/russian.htm

EDIT again: Not much info in my post, just wanted to point the fact that I thought is the idea in this device: It displays two things in one display, the reference and your playing!

[austin]

I'm starting to design a tremolo in wich the lfo starts when guitar signal is present, and it will start on the full amplitude part of the waveform.

Another possibility is to make the circuit so that when  it comes out of bypass, the LFO gets reset.  I think the zvex seq effects might do this?