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Old 8th Aug 2022, 12:33 pm   #1
Martin Bush
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Default Piezo transducers

I am starting from a zero-knowledge base here, so bear with me.

I have a Casio keyboard into which you can plug drum pads. These pads were sold separately at the time and would now cost twice what the keyboard cost for me to buy.

However I believe that you can make your own triggers using Piezo transducers and I have seen a video on it (the trigger is actually used on another piece of gear but I think the principle is the same).

The method is simply to stick the piezo disc to a piece of firm cork, then stick some rubber mouse mat over that. The person in the video uses hot glue and spreads it all over, including on the piezo disc. Solder an appropriate piece of lead and jack plug to the piezo, hit the thing and it triggers the drum machine.

I want to do the same thing...

Firstly, is does the above method sound right? I know that my Casio sounds are triggered by voltage - is that what the Piezo produces?

Second, does the method above sound like the best way to get a reliable trigger (ie, would glue on the piezo be OK?)
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Old 8th Aug 2022, 10:32 pm   #2
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Default Re: Piezo transducers

That sounds about right to me - they do produce a voltage but are usually used with high impedance inputs. I've experimented with piezo transducers into various devices (like the Alesis D4 and a Nomad P2M trigger box) but I've never got as far as making up proper pads.

The reliability depends very much on the sophistication of the device you are plugging them into. The Alesis D4 works very reliably but the Nomad was very difficult to use successfully.
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Old 8th Aug 2022, 10:44 pm   #3
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Default Re: Piezo transducers

The device is a Casio MT 205...

What I have found is that plugging in my headphones triggers the drum sounds - just once as the plug makes contact. So I have learnt something there.

What sort of voltage does a piezo transducer produce? I have seen them triggered with 'a voltage' but no mention was made of what voltage that would be. I believe the pads made to go with the keyboard weren't powered.
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Old 8th Aug 2022, 11:04 pm   #4
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Default Re: Piezo transducers

Some piezo elements make quite a bit of voltage. Have a look at a gas hob lighter, that makes a spark about 3 mm long. Ceramic piezo elements are used on record players and can range from something in the vacinity of 100 mV to probably half a volt. I have some piezo speaker elements which are circular brass ( I think ) disks with the piezo element glued on ( I think ) . They used to cost about $3 when I bought them. I have never tried to make them work in reverse. They should still be available at the normal auction sites and a few bucks spent experimenting will soon teach you what you need.
The come in a multitude of sizes and shapes.

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Old 8th Aug 2022, 11:09 pm   #5
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Default Re: Piezo transducers

You could try some of the cheapo brass disks with piezo material stuck to them, often used in cheap sounders or even as accelerometers in things like contact guitar tuners. If you search ebay using the phrase 'piezo sounder' you'll find loads.
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Old 8th Aug 2022, 11:34 pm   #6
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Default Re: Piezo transducers

That is the type I have in mind. Ive only ever seen them used to make buzzing sounds until recently, but since seen a video of them lighting a bulb and so on.
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Old 8th Aug 2022, 11:41 pm   #7
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Default Re: Piezo transducers

Years ago there was a magazine that did a drum project using piezo's - I don't remember if it was a UK or Australian (or possibly US) magazine but if I get time I will see if I can dig it up (I will be out most of today).
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Old 8th Aug 2022, 11:49 pm   #8
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Default Re: Piezo transducers

Thanks Terry, that will be interesting.
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Old 9th Aug 2022, 4:42 am   #9
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Default Re: Piezo transducers

Quote:
Originally Posted by Terry_VK5TM View Post
Years ago there was a magazine that did a drum project using piezo's - I don't remember if it was a UK or Australian (or possibly US) magazine but if I get time I will see if I can dig it up (I will be out most of today).
I think there was a Maplin project for something like this which suggests it might have appeared either in 'Electronics the Maplin Magazine' or 'Electronics and Music Maker'
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Old 9th Aug 2022, 5:21 am   #10
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Default Re: Piezo transducers

Here's what I've found so far (will check Maplin later):

ETI (Australian edition) October 1984 - analogue but uses an XR2206 - may be hard to find now. Mag available on World Radio history site.

The next two are more involved and use a PIC micro - first one is MIDI out (or possibly Sync input if your synth has it)

Bongo Box EPE July 2004

And this one has MIDI or as an input to a computer.

MIDI Drum Kit Silicon Chip Nov 2005 to Feb 2006 or EPE December 2007 to March 2008

There are also various options on the various DIY musical instrument sites but most seem to be aimed at MIDI only.

Edit - The Maplin one is Syntom page 48 here https://worldradiohistory.com/UK/Map...1990-06-07.pdf
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Old 9th Aug 2022, 8:47 am   #11
Martin Bush
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Default Re: Piezo transducers

That magazine is excellent - what a shame things like that don't really exist these days.

On the subject of the drum triggers, I have done a bit more searching online. It's amazing what saying the same thing but using slightly different words can throw up.

It's suggested elsewhere that the sounds are triggered by shorting signal to ground. So it seems that a momentary switch connected to a 3.5mm jack would work. That would also explain why when I tried plugging my headphones in to the trigger socket there was a sound.

Either way, I don't currently have either piezo transducers or momentary switches to hand so will have to order some bits.
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Old 9th Aug 2022, 9:16 am   #12
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Default Re: Piezo transducers

Why not conductive rubber pads?

It would seem the harder you hit the lower the resistance and the rate of change would be more proportional to the building pressure from the stick.

The attack and decay must matter. I don't know how much of that you get from piezo.
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Old 9th Aug 2022, 9:21 am   #13
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Default Re: Piezo transducers

Are they something I could find easily and cheaply? It would be interesting to try out at the very least.

I should stress that the drum sounds are very much on or off - there is no attack or decay.
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Old 9th Aug 2022, 10:38 pm   #14
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Default Re: Piezo transducers

Quote:
Originally Posted by Martin Bush View Post
On the subject of the drum triggers, I have done a bit more searching online. It's amazing what saying the same thing but using slightly different words can throw up.

It's suggested elsewhere that the sounds are triggered by shorting signal to ground.
That's not how the drum triggers that I've used work. They require a voltage pulse to work. They will also often work with an audio signal so that you can trigger a drum sample from the sound of a drum kit.
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Old 9th Aug 2022, 10:41 pm   #15
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Default Re: Piezo transducers

At this point I must bow to those with greater knowledge. Forget rubber pads particularly if "ramp" is not beneficial.
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Old 9th Aug 2022, 11:59 pm   #16
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Default Re: Piezo transducers

So, one quick experiment later and I have the answer.

I took a 3.5mm jack lead and shorted signal to ground using the nearest available item - an HDMI lead - and I got a bongo!

I must stress that this Casio keyboard is almost a novelty as far as the drum sounds are concerned, so the fact they trigger in this way I suppose is just a quick and cheap way to add a feature. I think the video I found showing them being triggered by a voltage was a coincidence - I think the person was making a circuit between signal and ground and thought the voltage was necessary.

I plan to try making a basic thing so I can 'play' the drums using some momentary switches and 3.5mm jack leads.

I have learnt a few things thanks to this thread which will come in handy.

Thanks to everyone for their input (pun semi intended).

Martin
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Old 10th Aug 2022, 6:09 pm   #17
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Default Re: Piezo transducers

According to the instruction manual, there are 4 sockets on the RHS of the unit and each can produce two drum sounds (e.g. high or low bongo) - I suspect using a stereo jack with either the tip or ring shorted to ground. Google says that the drum kit specified (model DP-1) has just switches.
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