Tap Tempo LFO with PIC 16F684

[ElectricDruid]

Hi All,
First post for me here. I'm a SynthDIY refugee.

Some time ago I did a voltage-controlled LFO project with a PIC 16F684. I put this online: http://www.electricdruid.com/index.php?page=projects.lfo9

Mostly I'd intended it as a modular synth module, but a few people wrote to me asking whether the chip would be usable as an LFO in effects circuits. They also asked whether it would be possible to add a Tap Tempo feature. Well, it's taken me ages, but I'm finally getting around to doing it. I've got a tap-tempo version of the above chip working on my breadboard already.

So what I'd like to know from everyone is "What features would you like to see on a LFO for effects use?". I'll try and include as many good ideas as I can.

Thanks,
Tom

[kvb]

multiple waveform output

are you going to be selling chips?

[RonaldB]

Hi Tom,
Nice to see you here.

A feature that would be helpfull is a ramp up and down in time.
And subdivisions for the tap tempo time.

thanks, looking forward to this one.

Ronald

[ElectricDruid]

KVB,
I might sell chips if people are interested. I've occasionally sold programmed chips to people without PIC programmers in the past when they asked me.

When you say "Multiple waveform output", do you mean simultaneous outputs? Currently the chip has one output which can be any of 8 waveshapes (ramp up/down, triangle, sine, square, sweep, spike, and noise).

RonaldB,

Subdivisions of tempo? Ok, I'll make a note of that one...

T.

[moosapotamus]

This sounds like a very cool idea. Agree, tempo subdivisions and multiple alternative waveforms would be great (sample & hold and/or random would be cool, too).

I don't recall ever hearing of a tap-tempo pedal that could do this, and it surely would be a challenge, but... How about a tap-pattern mode? IOW, maybe a rotary switch could be used to set the number of taps for the chip to accept as a pattern (ie- 3, 4, 5, 6, 7, 8 ). Now, suppose you set it to 5. Then, corresponding to the last five taps that you make, whatever timing differences you tapped in would be repeated. For example... 1 - - - 2 - - - 3 - 4 - 5. Actually, I guess if you set it to 5 you would probably have to tap 6 times in order to get the timing for going back to step 1 from step 5 in the pattern. Anyway... just a wacky thought.

What is the sweep waveform? Similar to ramp or saw?

What is the noise waveform... white, pink, etc.? Is there really any tempo associated with noise?

Any constraints on the duration of each tap or the number of taps needed to set or change the tempo? The more idiot-proof the better.

~ Charlie

[moosapotamus]

What is the sweep waveform? Similar to ramp or saw?

What is the noise waveform... white, pink, etc.? Is there really any tempo associated with noise?

Oh, okay... just looked at your web page. thx

~ Charlie

[ElectricDruid]

Charlie,

The sweep waveform is essentially the bottom half of a sine wave, repeated. It's supposed to be a good waveshape for flangers as it doesn't loiter at the top of the range. I haven't tried it.

Your idea of tap-patterns is definitely possible. My biggest fear would be that it might get a bit unwieldy to use. I want to try and keep the controls as simple as possible. But not simpler.

Currently the chip is set up so it measures the time between two taps. E.g. First tap it starts counting, second tap it stops counting and sets the frequency. You can either count yourself in ("1", "2", "3"+press, "4"+press), or you can have two goes and press on each beat. It'll time between taps one and two, and then between three and four, and use the latest tempo.
This means that you can feed it 0-5V pulses from other equipment (an old drum machine or synth, for example) and it'll syncronise the LFO to the incoming pulses.

Does anyone really need multiple simultaneous outputs, or are people just interested in having a good range of waveforms available on a single output?
T.

[kvb]

naw, I wasn't thinking that there would need to be multiple simultaneous outs.

But one more waveform idea is the opposite of what you said the sweep is - like a bunch of humps - this is good for filters and tremelo.

As far as buying a chip goes - it's either that or about two years of me trying by myself.

the sync function sounds good.

[moosapotamus]

Yeah, that pattern idea just kind of jumped into my head while I was typing my other questions... probably a little bit over the top.

I think my only interest in having multiple outputs would be a dual LFO that would allow you to do things like adjust the phase relationship between the two continuously on the fly with a pot, and select the waveform for each of the two outputs independently, as well as the tempo subdivisions. Maybe that's a little over the top, too? But if it's not, I would definately line up to buy a few of those chips.

The sync function does sound useful. If I understand, the tempo gets continuously reset for every pair of taps? What happens if tapping manually and you tap in an odd number of taps?

~ Charlie

[ElectricDruid]

Charlie,

"If I understand, the tempo gets continuously reset for every pair of taps?"
Yes, exactly.

"What happens if tapping manually and you tap in an odd number of taps?"
The chip will continue at the last known tempo whilst it waits for a second tap. If you tap again within 65 seconds, it sets the tempo based on that interval - hence it is possible to set extremely slow oscillations. This isn't a carefully designed limit - just a side effect of measuring milliseconds with a 16-bit variable (65535 mSecs). Perhaps it should be less.
If you wait longer than 65 seconds, it resets and ignores the "spare" tap.

BTW, KVB, I like the "humps" idea too. Thanks.
T.

[moosapotamus]

Sounds great, T.

~ Charlie

[RonaldB]

KVB,
I might sell chips if people are interested. I've occasionally sold programmed chips to people without PIC programmers in the past when they asked me.

When you say "Multiple waveform output", do you mean simultaneous outputs? Currently the chip has one output which can be any of 8 waveshapes (ramp up/down, triangle, sine, square, sweep, spike, and noise).

RonaldB,

Subdivisions of tempo? Ok, I'll make a note of that one...

T.

Yes Tom, subdivisions of what you tap. So you tap in 1/4 notes and get out 1/16 notes.

The subdivisions i would like are:
1/4
1/8
1/16
1/4*
1/8*
1/16*
1/4T
1/8T
1/16T

Just an example.

And i like the idea of Charlie about the Tap Pattern, I played with that to for a while on my arduino tap tempo controller.

best regards
Ronald

[G. Hoffman]

Does anyone really need multiple simultaneous outputs, or are people just interested in having a good range of waveforms available on a single output?
T.

Actually, I would.  Not a whole bunch, but two outputs which could be variably out of phase with one another would be useful.  They don't need to have different waveforms, just the variable phase relationship.  180 degrees would be easy to do with an inverting buffer, which is PROBABLY the most useful phase relationship, but I think I'd like to have others available, if possible.  Alternatively, how about some way to sync two chips?  With a variable phase relationship, of course.

The other thing that I would find useful would be a rhythmic amplitude modulation, i.e., the ability to change the amplitude of every (variable number) wave.  So, for instance, every other wave has a higher amplitude, or every third wave has a lower amplitude.  Does that make any sense?

For what it's worth, I want to use this to drive a tremolo in a stereo tube guitar amp. 



Gabriel

[sinisterguy]

this is quite intriguing. I've been wanting to do something like this for a tremolo project as well. I do agree that subdivisions are a good idea though. the S&H feature could be cool for a tremolo too. or even having using the output as a controller for an expression pedal input. it could be like a diy empress tremolo on steroids 

[G. Hoffman]

this is quite intriguing. I've been wanting to do something like this for a tremolo project as well. I do agree that subdivisions are a good idea though. the S&H feature could be cool for a tremolo too. or even having using the output as a controller for an expression pedal input. it could be like a diy empress tremolo on steroids 

That's what I was thinking, but you could do some interesting Flange and Chorus effects with it too.



Gabriel

[JKowalski]

I figured I should put my post in this one too, both as a bump to generate more interest in it and to double the chances of you reading this:


If you ever spent the time to get this off the ground, you could seriously make alot of money with this. I'd be willing to pay up to $10 for one pre-programmed, seeing as the part itself costs a mere $1.40 on bulk on mouser. Although I would buy many more if they were around $7, which I think is very reasonable. That's still a 500% profit, for not much work at all, provided you have a interface and a code set up for transferring!

[JKowalski]

This topic should be moved into the building your own stompbox forum, seeing as how it is meant for people who are not familiar with PICs. He is asking the community that has no experience with them what they would like to see in a preprogrammed chip that he could sell off to them.

In short, the target audience for the project & topic does not even venture into this forum. 

[Taylor]

This topic should be moved into the building your own stompbox forum, seeing as how it is meant for people who are not familiar with PICs. He is asking the community that has no experience with them what they would like to see in a preprogrammed chip that he could sell off to them.

In short, the target audience for the project & topic does not even venture into this forum. 

Agree. I am one of these people. I occasionally pop in here as part of my effort to know what I don't know - the first step in learning is learning what you need to learn.

[David]

Druid:

What is the possibility of using this setup to determine a beats-per-minute count and send the count out serially?

[jacobyjd]

Just to chime in with others--if this ended up looking like a 1-stop shop, multi-shape LFO in a single-chip format w/ minimal external parts and tap tempo, I would absolutely be in for one. In fact, I would consider converting my pedalboard setup to use a remote LFO plugin, and I would keep the LFO in its own box with a tap switch. I would use the LFO to sync up multiple modulation pedals from a central point.