# Using a piezo to trigger sounds from ‘Triggered MP3 Player Board’

#### Altouna

Joined Sep 9, 2020
14
Hello!
I’m working on a project the goal of which is to use my DIY piezo-based trigger to trigger sounds from the ‘Triggered MP3 Player Board’ located here:
https://www.electronics123.com/shop...d-with-10w-amplifier-and-terminal-blocks-8267

The piezo's I'm using are these:
https://www.amazon.com/Luvay-12Pcs-Pickup-Transducer-Prewired/dp/B0775V78D1/ref=sr_1_3?crid=1GT6X08KKRVYM&dchild=1&keywords=piezo+trigger&qid=1599664223&sprefix=peizo+,aps,157&sr=8-3

I was able to find a tutorial that showed how to use button-style triggers to trigger the sounds, but I’m a drummer and would prefer to use my piezo-based trigger that I strike with a drumstick instead of using a button trigger.

Will a piezo work in place of a button trigger? Will I need to use alternate wiring or do I need to figure out how to make the button trigger work?

Thanks very much!
Alto

#### MrSoftware

Joined Oct 29, 2013
2,070

Joined Jan 15, 2015
7,143
Depends on what the push buttons do. Looking at the board bottom it looks like you would use Normally Open push buttons from button terminal to ground. If that is how it works then I can see trying a NPN transistor like a 2N2222 Collector to button terminal and emitter to ground. Then a small signal conditioning circuit from your transducer to drive the transistor. Several ways to go about it assuming I have a good guess as to how it works.

Ron

#### Altouna

Joined Sep 9, 2020
14

#### Altouna

Joined Sep 9, 2020
14
Depends on what the push buttons do. Looking at the board bottom it looks like you would use Normally Open push buttons from button terminal to ground. If that is how it works then I can see trying a NPN transistor like a 2N2222 Collector to button terminal and emitter to ground. Then a small signal conditioning circuit from your transducer to drive the transistor. Several ways to go about it assuming I have a good guess as to how it works.

Ron
Thank you, Ron. First thing I'm going to do is check the piezo's on a multimeter (set to ohms) to see if the multimeter maxes out when the peizo is struck. If so, I should be able to use the piezos with no modification. If not, I'll need to figure out how to build what you suggest in your comment!

#### Bernard

Joined Aug 7, 2008
5,784
You will get poor results with a multi meter on ohms or V, just a slight tick. With O scope it will show a damped wave of around 10 V PP depending on how hit. Piezo will easily trigger a 555 pulse generator with a supply of 5 to 12V, or other.

#### Bernard

Joined Aug 7, 2008
5,784
'Found old drawing for paper target using piezo sensor. R 4 any thing from 100k to 1M. Could
use 5k to 100k for R2 & can skip R1 &R, or if tapping close to piezo just bias pin 2 to 1/2 supply V with 2- 100k Rs & skip R4. At top of this page find " Search Forums" Enter Paper Target then hit Search.

Joined Jan 15, 2015
7,143
I would try the circuit Bernard posted. The negative spike from your sensor should trigger the 555 for a one shot positive pulse. Use that pulse in conjunction with a transistor (NPN) as I mentioned previously. I am also guessing that the buttons on your module only require a quick momentary "tap" to play a selection.

Ron

#### Altouna

Joined Sep 9, 2020
14
I appreciate the detailed response, Ron! Unfortunately, my knowledge doesn't run this deep and I'd have a very hard time building the circuit you suggest. I might end up having to purchase button switches (that per the documentation will work) and modifying my trigger apparatus to work with the button switch. Thank you, though!!

#### Bernard

Joined Aug 7, 2008
5,784
Are you planning on using all 4 switch inputs ? How will piezos be mounted ?
What country are you in ?

#### Altouna

Joined Sep 9, 2020
14
The plan is to connect 1 piezo to each of the 4 switch inputs to be able to trigger 4 different sounds. Each piezo will be glued to a piece of metal which will be glued to a matching size rubber surface that is struck with a drum stick to trigger the sample.

I'm in the US.

I appreciate the help! Thanks for taking the time to consider my dilemma!

#### Sensacell

Joined Jun 19, 2012
3,134
Beware that MP3 is not the best format for "triggered" sounds- MP3 is a complex compression algorithm, it needs time to wind up and start playing the sound.
WAV files play instantly, they are totally uncompressed, but of course, take much more memory space.

#### Altouna

Joined Sep 9, 2020
14
Beware that MP3 is not the best format for "triggered" sounds- MP3 is a complex compression algorithm, it needs time to wind up and start playing the sound.
WAV files play instantly, they are totally uncompressed, but of course, take much more memory space.
Good point. The board supports WAV files, and the samples I plan on using are short (no more than maybe 3-4 seconds each), so even if I use uncompressed WAV files I don't think I'll have a space issue.

#### Bernard

Joined Aug 7, 2008
5,784
I made a simple test with 2 - 2.5 oz. plates mounted on soft foam with piezo mounted on one plate. Piezo black to ground, red to anode of 1N4148 diode, cathode to base of MPSA14 darlington transistor with 100k Rs either side of diode to ground. Collector load 4.7k to 6V supply.
A tap on piezo plate gives a 10 ms. neg. pulse or rather about 10 - 1ms. pulses. Filtering with .001
to .01 = no change, .1 starts loading piezo. This might work with function #2, Pulse non- interruptable, but might not work with 0. Will think some more.
What is supply voltage ? What is V from ground to key contacts?

#### Altouna

Joined Sep 9, 2020
14
I'm sorry, but my technical knowledge is nowhere near sufficient to understand most of what you just said! I can tell you the specs of the board itself are:
• Working voltage: DC 8V-24V
• Working current: ≤400mA (Input: DC12V DC)
• Working current if playback through headphone jack only: 30mA (Input 12V DC)
• Standby current: 10mA (Input 12V DC)
• Power Consumption: ≤10W
I'm not sure if this is what you're looking for, my apologies if not.

#### Bernard

Joined Aug 7, 2008
5,784
I'll assume you will use 12 V supply. I think that I have a circuit that will fit your project assuming that you already have the piezo's, mounting plates & foam. Would use a LM339, 4 comparators,
to detect piezo pulses, 4049 IC X 6 inverter, & 4066 analog- digital switch X 4. The 4066 might have switch resistance up to 200 ohms.
A new day has dawned & I'm back to post #8 as maybe best solution.
Do you have the MP3 in hand ?
With piezo mounted on a plate. pulse amplitude is much reduced, so will re bread board with a 555 with mounted piezo. Plate( curtain weight ) 2.5 oz., 2" X 3.4" X .081".
If successful I can supply a board for $5.00 + parts ( about$6 for parts, plates, if wanted, no charge except for increased postage. ) & postage.

#### Altouna

Joined Sep 9, 2020
14
Much appreciated! The board itself just arrived and, as suspected, the peizo doesn't work to trigger the sound file. I grabbed a button switch from my kids 'snap circuits' set and, also as suspected, it works perfectly. I should have pursued the idea of using piezos as triggers more thoroughly, but you live and you learn I guess. I'm going to purchase a couple of flat-style button switches from my local electronics store and modify my trigger system to work with those. I really appreciate you sharing your knowledge and electronics insight. I learned alot in a few short days! I'll post a link to the completed project in case you're interested in seeing what I eventually came up with. Thanks again...!

#### Bernard

Joined Aug 7, 2008
5,784
The 555 combo works just fine for future ref. 'Looking forward to final report.

#### MrSoftware

Joined Oct 29, 2013
2,070
As mentioned above, this can be made to work. The link I posted above shows how to do want using a piezo and an arduino. Worst case you can do the same and use the arduino to trigger your sound board.