Madbean Tappy (ElectricDruidTAPLFO3) Mods?

[Pish]

Hey!
I recently found the Tappy on Madbean which then led me to look at the datasheets for alot of stuff from Electric Druid.(all clever and really in my lane, guitar/synthy) I'm a mere kit builder but I'd like to try add some functions to this.
As from looking at the data sheets I believe it's possible to maybe add some stuff but I have questions as Im not exactly up to scratch!
https://www.madbeanpedals.com/projects/_folders/TapTempo/schematics/Tappy.gif

The Tappy project takes care of most of the heart of what is shown in the TAPLFO3 Datasheet. So here is the questions about what I'd like to add,

1) In the Filter FX/PT Wobble Delay LFO selchematic it shows the optional expression/0-5v CV input. Can the same be applied to the Tappy circuit on any of the main parameters? Would anything need to be added to stop over voltage?
Also if I deem not worth an expression pedal, could I just put a switch jack where J11/12 is?

https://electricdruid.net/wp-content/uploads/2018/03/FilterFXSchematicPg2.jpg


2) The TAPLFO3 has clock output from the chip. Does this require anything after it or can it go straight to a Jack? (Clock in is already given in datasheet, thank you)


3)  I can see on the STOMPLFO datasheet that it puts out PDM not PWM. But you can get a 2-7v LFO output on it with a SallenKey Filter. The TAPLFO3 shows the same.
So, can I use the passive filter from the STOMPLFO on the TAPLFO3 to get 0-5v?
Or is the SallenKey better?... basically my thinking is that, most pedals that accept CV are 0-5v then if I'm interfacing with synth stuff I can then amplify/offset with that to get a bigger range using the synth kit anyways.

If anyone could help that would be grand.
Have a good day

Cheers

[ElectricDruid]

<hand shoots up>Oooh, Oooh, I know this one! <jumps up and down in seat a little bit>

1) In the Filter FX/PT Wobble Delay LFO selchematic it shows the optional expression/0-5v CV input. Can the same be applied to the Tappy circuit on any of the main parameters?

Yes. All the CV inputs on the chips (TapLFO/StompLFO/whatever) are the same - just 0-5V ADC inputs, so you can mostly take ideas from one chip and freely apply them to other chips. (You've managed to come up with one example where you can't - we'll come to that...)

Would anything need to be added to stop over voltage?

Yes, this has to be considered. Luckily the PIC chip designers added over-voltage protection on the chip, so we don't absolutely have to. However, the diodes they used for this can't handle huge currents, and if the over-voltage protection dies, the chip dies, or at the least that input pin. That's why the FilterFX schematic you linked to shows a 2K2 resistor in series with the input. There's a cap too, so it acts as a lowpass filter as well, but the most important function it has is to limit the current that can flow to a safe level for the over-voltage diodes if you hit the input with more voltage than you should. In other schematics I've used 4K7 (like the VCDO) for this, but that's overkill and 2K2 is sufficient.

Also if I deem not worth an expression pedal, could I just put a switch jack where J11/12 is?

Yes. The J9-J13 connections were intended for a switched jack so the Freq control is in circuit if nothing is plugged in, or you can replace the freq control with an expression pedal, or you can plug in a mono cable with a 0-5V CV. I have 3.5mm to 6.35mm mono leads in my workshop for this, so I can get CVs out of my Eurorack modular into my pedals.

2) The TAPLFO3 has clock output from the chip. Does this require anything after it or can it go straight to a Jack? (Clock in is already given in datasheet, thank you)

You could perhaps add a 1K in series as some basic protection against the output getting shorted. The chip's outputs can drive up to 20mA, so they're pretty robust. I have managed to kill a few over the years, but only a handful over a decade or more.

3)  I can see on the STOMPLFO datasheet that it puts out PDM not PWM. But you can get a 2-7v LFO output on it with a SallenKey Filter. The TAPLFO3 shows the same.
So, can I use the passive filter from the STOMPLFO on the TAPLFO3 to get 0-5v?
Or is the SallenKey better?... basically my thinking is that, most pedals that accept CV are 0-5v then if I'm interfacing with synth stuff I can then amplify/offset with that to get a bigger range using the synth kit anyways.

For the TapLFO, the active filters are better (and there are various designs scattered around my datasheets - you could have a look at the VCLFO too, for example). That's because the TapLFO uses PWM at a frequency of 31.25KHz, so the PWM frequency is above audio, but only just. Hence it needs decent filtering.
In the case of the StompLFO, the output frequency is variable, but mostly in the 100s of KHz/1-2MHz range. If you use a simple passive filter for that, you still get excellent reduction of the PDM frequency, so you can be more lackadaisical!
This output frequency difference is one example where you can't simply swap stuff back and forth between chip designs and expect it to work the same. On the input side, I don't think I can think of a situation where this is true.

BTW, the reason the example Sallen-Key filter provides 2-7V instead of 0-5V is that 2-7V is a fairly typical output for a op-amp based LFO, so the given circuit can be used pretty directly in a number of pedal designs to replace the common Schmitt trigger/integrator LFO circuit; just pull that one out and drop this one in.

Doing a solid 0-5V output on a 0-9V single supply on the other hand is actually much more difficult since most common op-amps can't drive the output that close to ground, so the bottom of the waveform gets clipped. There are chips that *can*, but you get to need specific op-amps rather than "anything out of the spares box". On a bipolar +/-12V supply (like Eurorack), this isn't an issue since you have loads more headroom, and you won't see any clipping until you get close to those 12V rails. The more synth-orientated circuits I've done generally assume a +/-12V or +/-15V supply and take advantage of that benefit.

I hope this helps, and enjoy the chips!

[Pish]

Wow! Thank you for the quick and in-depth reply.
Have a brilliant week and thank you for putting these cool doodads out! 


Edit.
Oh other question I forgot, but have no kind of reference about,
Instead of anything mentioned could this control a digital potentiometer?

Also, what spec am I looking for in a datasheet for the appropriate 0-5V or can I add something to the 2-9V to offset or attenuate it? For example, one thing I'd like to mess with is a EHX pitch fork which takes 0-5v and I don't know if it has protection


Edit edit
Or maybe I'm coming at this the wrong way? Maybe I'm better with a Switching Meanwell supply that converts 9v to +/-12 or 15.
I'm trying to stick with the 9v in because of guitar pedals.