Let's design a tap tempo tremolo.

[JKowalski]

I used this crystal from Mouser (although I bought mine from Newark):

http://www.mouser.com/Search/Refine.aspx?Keyword=73-XT49S2000-20

If I recall correctly, I chose them because they were shorter than most of the other crystals I saw. You can see them in this image and this image.



MIke

Used the same, think it was the cheapest and smallest on mouser.


Taylor, what are you doing with pin 8 of the PIC chip? It's typically unused but suits itself nicely to modifications. It might be useful to modify the board to allow future options on this pin (ex. that waveform select switch I added on one of my mods)

For example putting an optional pullup to V+ on that pin and a pad to connect externally would give the option of adding a momentary switch to it.

Just to give you an idea it is a very versatile pin, it can be used for a CV input, or digital I/O.

[Taylor]

Ok, I'll do that.

Edit: done. 

[ElectricDruid]

Just a note to say in public that I'm sorting out chips for Taylor, so he'll be able to supply programmed chips with the PCBs for anyone who wants one.

If you're into PICs (or would like to be), you're still free to download the code from either me or JKowalski's site, and then you can play with it too. But if you do anything really cool, be sure to tell us all about it!

My site, with my original code:
   http://www.electricdruid.com/
The Kowalski variations!:
   http://strangedesigncs.heliohost.org/

T.

[Taylor]

Yep, I'll sell the chips along with the PCBs so you can avoid double shipping charges.

JKowalski mentioned to me that there is an unused pin on the chip which could be put to use. Anybody have any thoughts on extra features we could add to this? His idea was a stomp switch to swap between tapped speed and the speed pot. I was thinking maybe a half time stomp would be good, or a stomp to cycle through time divisions.

[G. Hoffman]

JKowalski mentioned to me that there is an unused pin on the chip which could be put to use. Anybody have any thoughts on extra features we could add to this? His idea was a stomp switch to swap between tapped speed and the speed pot. I was thinking maybe a half time stomp would be good, or a stomp to cycle through time divisions.

Well, I'm not exactly a prospective customer, as my favorite part of this whole electronics thing so far is designing circuit boards, and I've already programed a few of these chips for bread boarding, but it seems to me that, as JKowalski has gone to the effort of creating several options, you might want to just have it go to a wire connection so people can chose different options.  If I remember right, at least one of JK's variations use a pot in that position, others a switch, and even if he hasn't yet, a pot is a possibility for future variations.  A small sub board, or possibly even just some point to point parts, would work fine for the functions of one pin.  Particularly as you have (I believe) already said the board was getting a bit crowded.

But as I said, mine is hardly the pertinent opinion on the matter.


Gabriel

[oliphaunt]

Sign me up for a couple of boards and chips !!  I will excited to see how this all turns out.

I would really love it if the board would fit in a 125B box, I don't mind tightly spaced footswitches.

Taylor can you provide a parts list as soon as the design is finalized so that we can order them ahead of time?  Thanks.

[JKowalski]

JKowalski mentioned to me that there is an unused pin on the chip which could be put to use. Anybody have any thoughts on extra features we could add to this? His idea was a stomp switch to swap between tapped speed and the speed pot. I was thinking maybe a half time stomp would be good, or a stomp to cycle through time divisions.

Well, I'm not exactly a prospective customer, as my favorite part of this whole electronics thing so far is designing circuit boards, and I've already programed a few of these chips for bread boarding, but it seems to me that, as JKowalski has gone to the effort of creating several options, you might want to just have it go to a wire connection so people can chose different options.  If I remember right, at least one of JK's variations use a pot in that position, others a switch, and even if he hasn't yet, a pot is a possibility for future variations.  A small sub board, or possibly even just some point to point parts, would work fine for the functions of one pin.  Particularly as you have (I believe) already said the board was getting a bit crowded.

But as I said, mine is hardly the pertinent opinion on the matter.


Gabriel

None of them use a CV on pin 8. I can't really think of any mod that might need a CV... The chip's got so many options already. A digital input seems the most useful, to allow more foot control over parts of the chip's operation.

I suggested that something might be put on the pin because I think most of the people ordering these boards will be doing so because they do not have the ability to program themselves, so... Adding another feature would let the people who can't reprogram to have something else available, and the people who want to reprogram can still do it with no issues...

I asked taylor earlier to put an optional pullup and pad of pin 8 so that you can use it as a digital input simply by connecting a mom. switch to ground the pin. Using it as a CV input, you could just not add the pullup and connect a pot to the pad instead. Using it as an output (say an LED) would be fairly easy.

If we can't think of anything terribly useful then I guess we can just forget it. But I did like the multiplier cycle control, that might be useful in a live setting.

[Taylor]

Yep, the board has a pad to access pin 8 with a pullup to 5v. So adding a momentary switch is already supported in the hardware, whatever the code does with it.

I'm thinking the most useful thing would be to cycle through multiplier settings, but the implementation would be tricky. Since this would be a performance control, it's important that it would maintain phase when stepping through multiply settings. So say I'm playing in a straight 4/4 time, using the 4 multiply. Then I step to 3 multiply to get a 3-on-4 feel. Then I click through to 2 multiply. At this point, at least if we assume that I stomped on the multiple select switch right on beats, the 2 multiply should be falling on the same beats as the 4 multiply was, except half as often. It shouldn't go out of sync when changing multiply settings.

So maybe the switch should simultaneously reset the wave phase and change multiplier? This would seemingly keep everything nicely lined up.

There's another concern that I think would be harder to deal with. If using a sine wave for example, it would be ideal if there wasn't a discontinuity heard when selecting multipliers and resetting phase. Ideally, it should smoothly blend from wherever the wave happens to be at the moment of the press to the beginning of the next wave. This might be as easy as a lowpass filter that's placed on the output of the wave only during the moment of phase reset. My digital knowledge is limited to DSP on the FV-1 (and just limited in general) so I don't know whether this would work for the hardware involved here.

Also, Chris, did either you or Tom ever address the thing I brought up a few pages back about where the start of each waveform table should be? Like, the sine and similar waves need to reset at their peak, but the square wave should reset at the positive-going edge?

[Taylor]

Sign me up for a couple of boards and chips !!  I will excited to see how this all turns out.

I would really love it if the board would fit in a 125B box, I don't mind tightly spaced footswitches.

Taylor can you provide a parts list as soon as the design is finalized so that we can order them ahead of time?  Thanks.

I'm pretty positive this will fit in a 125b, unless you want the third footswitch we're discussing above. So we'll give ZVex a run for his money.

I'll get a real parts list together soon. Here's the automatic one my CAD program spit out:

item qty       part type       values

1   14   box metal film cap   22P   100NF   100NF   100NF   1UF   330P   1UF   100NF   100N   100NF   

               330NF   100NF   22P   XTAL   

2   1   DIP14      TAPLFO   

3   1   DIP8      TL072   

4   1   DO34      1N4001   

5   2   ELECTRO      10UF   100UF   

6   1   OPTO      OPTO   (haven't figured out the right opto yet, will need to experiment when I get the proto boards)

7       4 or 5       potentiometer           B10k all

10   19   resistor      1M   10K   220K   220K   1M   1K   150R   1K   10K   1K   

               100K   150R   10K   10R   100K   10K   3K6   EXP   1K   

11   2   TO-92                  78L05   2N3904   

12   1   TRIM_MINI      10K   

[G. Hoffman]

JKowalski mentioned to me that there is an unused pin on the chip which could be put to use. Anybody have any thoughts on extra features we could add to this? His idea was a stomp switch to swap between tapped speed and the speed pot. I was thinking maybe a half time stomp would be good, or a stomp to cycle through time divisions.

Well, I'm not exactly a prospective customer, as my favorite part of this whole electronics thing so far is designing circuit boards, and I've already programed a few of these chips for bread boarding, but it seems to me that, as JKowalski has gone to the effort of creating several options, you might want to just have it go to a wire connection so people can chose different options.  If I remember right, at least one of JK's variations use a pot in that position, others a switch, and even if he hasn't yet, a pot is a possibility for future variations.  A small sub board, or possibly even just some point to point parts, would work fine for the functions of one pin.  Particularly as you have (I believe) already said the board was getting a bit crowded.

But as I said, mine is hardly the pertinent opinion on the matter.


Gabriel

None of them use a CV on pin 8. I can't really think of any mod that might need a CV... The chip's got so many options already. A digital input seems the most useful, to allow more foot control over parts of the chip's operation.

I suggested that something might be put on the pin because I think most of the people ordering these boards will be doing so because they do not have the ability to program themselves, so... Adding another feature would let the people who can't reprogram to have something else available, and the people who want to reprogram can still do it with no issues...

I asked taylor earlier to put an optional pullup and pad of pin 8 so that you can use it as a digital input simply by connecting a mom. switch to ground the pin. Using it as a CV input, you could just not add the pullup and connect a pot to the pad instead. Using it as an output (say an LED) would be fairly easy.

If we can't think of anything terribly useful then I guess we can just forget it. But I did like the multiplier cycle control, that might be useful in a live setting.

Makes sense.  Though, really, the pads you need for either a pot or a switch are the same - one for +V, the pin itself, and ground.  It would be pretty easy to put in pads for either, and wouldn't take up much extra space.


Gabriel

[Taylor]

I don't think you need to ground the pin when not connected to V+, you can just leave it floating, right?

[MoltenVoltage]

I don't think you need to ground the pin when not connected to V+, you can just leave it floating, right?

[Taylor]

I still consider myself a noob with electronics

I reserve the right to be very wrong. However, I thought that that's what JKowalski told me, but there's a good chance I misunderstood.

[G. Hoffman]

I still consider myself a noob with electronics

I reserve the right to be very wrong. However, I thought that that's what JKowalski told me, but there's a good chance I misunderstood.

Even if it's possible, it is always better to give a pin on any IC a definitive reference.  Now, you could have it tied to ground or to V+ internally by programing it appropriately (or so I assume, since that is what Molten Voltage has done with the MV-53).  But even then, you may as well tie it to the appropriate rail. 

Or at least, that is the way I understand it.  I too could be very wrong.


Gabriel

[MoltenVoltage]

make unused pins an output and send low and don't connect to anything

[Jaicen_solo]

Perhaps you could use it as an inverted (phase) output, to make stereo delay easier. Or even better, you could perhaps have it function as a multiplied/divided output. That way you could have a trem doing 1/4's on the left, and 1/16's on the right, or whatever. 

[flo]

The unused pin can not be setup as PWM so it can't provide an LFO output. So best use would be for some sort of control input.

[JKowalski]

Yep, the board has a pad to access pin 8 with a pullup to 5v. So adding a momentary switch is already supported in the hardware, whatever the code does with it.

I'm thinking the most useful thing would be to cycle through multiplier settings, but the implementation would be tricky. Since this would be a performance control, it's important that it would maintain phase when stepping through multiply settings. So say I'm playing in a straight 4/4 time, using the 4 multiply. Then I step to 3 multiply to get a 3-on-4 feel. Then I click through to 2 multiply. At this point, at least if we assume that I stomped on the multiple select switch right on beats, the 2 multiply should be falling on the same beats as the 4 multiply was, except half as often. It shouldn't go out of sync when changing multiply settings.

So maybe the switch should simultaneously reset the wave phase and change multiplier? This would seemingly keep everything nicely lined up.

There's another concern that I think would be harder to deal with. If using a sine wave for example, it would be ideal if there wasn't a discontinuity heard when selecting multipliers and resetting phase. Ideally, it should smoothly blend from wherever the wave happens to be at the moment of the press to the beginning of the next wave. This might be as easy as a lowpass filter that's placed on the output of the wave only during the moment of phase reset. My digital knowledge is limited to DSP on the FV-1 (and just limited in general) so I don't know whether this would work for the hardware involved here.

Also, Chris, did either you or Tom ever address the thing I brought up a few pages back about where the start of each waveform table should be? Like, the sine and similar waves need to reset at their peak, but the square wave should reset at the positive-going edge?

Hi, I'll look into the things that you mentioned this weekend. I've had a rough week and haven't had much time to work on anything.

I don't think it will be possible (well, easy) to come up with a solution to the discontinuity during phase resets. Although I will try to figure something out for the multiplier change... so that it only activates the change when the phase ends back up at zero.

I think the wave phase start issue was never resolved, again I will look into it and change it if necessary.


So what's the decision as far as the unused pin? It's up to you in the end, Taylor.

I have another suggestion to throw out there, and that is whether or not the random waveform should be kept.

Molten Voltage, that would be a good plan but you invite the risk (though small) of damaging the not-so-easily replaceable chip by hitting the pins with a voltage.... *shrug*

And Gabriel, the PICs do have weak internal pullups but they are only on PORTA for the PIC16F684, if I remember correctly. Not the unused pin.

[Taylor]

I think Tom is working on the multiplier step switch. He also says that the wave thing is fixed in his code, I think he had to take your code with the wave distort and the phase thing and put them together. So you guys could discuss it, but I think he's on it.

[ElectricDruid]

I am indeed!

I've been tinkering about with it this afternoon, and I've got Version 2 code up on my site:

http://www.electricdruid.com/index.php?page=projects.taplfo

This includes the Wave Distort CV that JKowalski put in, and my adjustments to wave start positions. It also uses pin 8 as a digital input to step through the multiplier settings.

Taylor, I can't work out if it'll do what you suggested with the taps - running at 4/4, you tap and go to triplets, count 3, tap and go to 8/4? Does that work out? Anyway, the chip does it, musical or not.

I think unless anyone has any unmissably great ideas or finds any bugs, I have to regard this as the final version and start getting some chips programmed. The alternative is that we spend forever tweaking and never get any units built!

Thanks,
Tom