Finger Drum Triggers - How to get them right?

[Stefan]

Hi there,

Now that I have finished my first MegaDrum module I would like to build some nice finger drum triggers with piezos.

I did already some trial and error and I have to say that it's not as easy. The response of the piezos is not really sensitive and reliable.

My first objectives would be to have some nice pads that
- are sensitive enough to even recognize gentle finger taps
- have good resolution of pressure level to voltage level
- are protected to unwanted interfering signals

Some basic questions arise:
1) Which piezo are the best for this purpose in terms of size, impedance, voltage, etc.?
2) How to wire the piezos? Which wires are recommendable? Shielded wires?
3) How to build the pad itself? What are the main points to considered for a sensitive pad?
4) What are the correct settings in the MegaDrumManager?

I suppose you guys have already quite an experience with the goods and bads of a lot of approaches.
I'd be happy if you could share the best practice with me!

Thanks and regards,
Stefan

[airflamesred]

1, The larger diameter ones (35mm) seem more sensitive to me rather than the 20mm. I think its easier to add more surface to dampen the signal, if that makes sense.
2, Don't think it matters
3, Experiment
4, You won't know until you congigure it. Put something together, along the lines of rubber covering on your piezo and test to see what the high level is. If it's too much (over 900) then add some more surface. That would be my start.

I don't recall anyone doing this kind of thing before here so I, for one, appreciate your postings as I'm sure others will in the future.

[Stefan]

Thanks airflamesred for your continuous support!

From what I understand so far a good pad is a combination of
1. the selected piezo (size, other features?)
2. the construction of the pad
3. the settings in the MegaDrumManager

During my first trial and error I have the impression that especially the construction of the pad does have a big influence. (Like how hard is the layer on which the piezo is attached, how flexible is the trigger side of the pad, how heavy and rigid is the whole assembly, etc.)

I am really curious how it is possible to have a pad with a nicely even and smooth sensitivity all over the surface. At the moment my first pads are not reacting homogenous at all.

I will tell if I have some progress.

And of course I appreciate your tipps!

Good night,
Stefan

[airflamesred]

I've had an idea, Stefan.
I can't do much for a few days because of the festivities but I've mounted a 20mm piezo inside a plastic water bottle top. It may need some damping but at 30mm dia it seems fit to the fingers.
Something like this? Then just drill through underneath to let the wires escape.

[Stefan]

Hi airflamesred,

That's a good advice, thanks! I will try it out as soon as I find some time.

I was trying out some finger triggers made of wood parts and rubber (see picture)... Not bad but then not sensitive enough for soft touch... Of course what I would like to have are triggers that register
1) every touch from gentle too hard
2) faster repetitive hits.

What is the best "working environment / assembly" for piezos to achieve this?

I will continue trying...

Happy holidays!

Stefan

[ignotus]

The less material there is between the piezo and the surface you strike, the more sensitive it will be; i.e., if you glue a piezo directly into a bottle cap I'd say it should be very sensitive. If you put a bit of rubber/foam in and then stick the piezo in it will be less sensitive, etc. But, if you make it too sensitive, it might max out easily too, so you have to find a balance. If a piezo can be sensitive enough to pick up very light hits when under a 30 mm foam cone (like when used in mesh head pads), it should be no problem at all to make a finger pad that picks up the lightest of hits - it'll just take some trial and error. You should also tell us what parameter settings you are using when doing your tests - don't just go with the default ones.

I reckon the biggest challenge with such a device will be minimising crosstalk - very sensitive triggers will also mean more crosstalk. You'll need to find a way to isolate the triggers from each other with soft foam or something.

I also like the bottle cap idea - you can mix and match different sizes and colours for different pad types.

Edit: Those blocks of wood are waaay too thick to transfer vibrations to the piezo. Also, if you need to raise sensitivity, stick the piezo on with a thin piece of foam that has the diameter of the ceramic part - that way you let the piezo oscillate a bit.

[airflamesred]

Some good points there, ignotus.
I actually think that crosstalk is not going to be an issue with this as even a hard strike from the finger is not going to cause that much vibration - we shall see.

And yes, when adding and removing bits of rubber etc during this experimentation, I would recomend setting the high level and threshold each time.

[Stefan]

Thanks ingots for the good points!

I think you are right, the more material on the piezo the less sensitive it will be.

I will try next with the bottle cap proposal from airflamesred.

In the MDM I don't keep the default settings. I adjust mainly the Threshold and HighLevel as recommended by dmitri.

Let's see if I can progress. I will keep you guys informed!

[airflamesred]

Ok,
I just glued the piezo inside without any cushoning.
Threshold 23
High level 500ish. This was on an atmega so the arm version and your finger strength may vary.
Crosstalk at 0
I can't find enough leads ATM to test crosstalk with a second piezo but with the threshold at 23 or even raising crosstalk level I couldn't get the piezo to trigger by hitting the surrounding wood. Perhaps some rubber between the body and the cap may also help with containing the vibration.

[ignotus]

Looks good! I reckon if you rest the triggers on a couple of sheets of EVA you could really do away with crosstalk and bring the threshold down to a point where it'd be incredibly sensitive.

On occasion I've toyed with the idea of making one of these but I just don't have the time... haven't even got round to properly finishing my e-kit after 8 years... Though I think it has more to do with the fact that there is ALWAYS something to add or improve - it never ends!