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Topic: Knock Sensors (Read 342 times) previous topic - next topic

RobFarley

Apr 08, 2019, 02:20 pm Last Edit: Apr 08, 2019, 02:39 pm by RobFarley
Hello,

So I'm trying to build a target for a nerf gun and need a trigger for when the target is hit...

I've bought 6 knock sensors:
Vibration-Sensor-Module-Arduino-Raspberry

But they seem to take way more of a whack than I want to make them work. Attaching them to the back of the target is very hit and miss (no pun intended), they also suffer quite a lot of bounce once they are triggered.

So I'm looking at trying these:
Piezoelectricity-Ceramic-Vibration-Development-Regard

Which look like they might be worth a try.

But they look like a very expensive version of this:
Celan-Quality-Piezoelectric-Ceramic-Loudspeaker

And looking at this:
https://www.arduino.cc/en/tutorial/knock

The latter looks like all I should need (and a couple of resistors).

Any help appreciated!
Here's a bit of a blog of my project so far...

Cheers, Rob
Cheers, Rob

Geek Emeritus

I would try a microphone first, then a sensitive accelerometer
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wvmarle

I've bought 6 knock sensors:
Vibration-Sensor-Module-Arduino-Raspberry

But they seem to take way more of a whack than I want to make them work. Attaching them to the back of the target is very hit and miss (no pun intended), they also suffer quite a lot of bounce once they are triggered.
Description gives you a clear clue already. It's a contact type sensor, so will bounce as long as your board bounces. You'll just need to do some filtering on that - just regular button debounce, possibly with increased debounce time, will do great.

Quote
So I'm looking at trying these:
Piezoelectricity-Ceramic-Vibration-Development-Regard

Which look like they might be worth a try.
Those sensors look much more promising, and will do the job much better, as long as you can get the impact energy to transfer to the disks. That part is much easier with your first sensor as those will simply vibrate with your target.

Indeed you don't need that breakout board, just a handful of resistors.
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RobFarley

Awesome, that's what I thought. Thanks for your help.
Cheers, Rob

pert

You'll want to have a good attachment between the target and the piezo disk so that the vibrations will transfer. The target should be of a material that will transfer the vibrations well. A piece of sheet metal is great. A piece of soft foam is not great. I used one of those basic piezo disks mounted to a piece of sheet metal to reliably detect impacts from 5 ft sample rolls of thin twine dropped from only about a foot. I'm sure the nerf packs much more of an impact so you might not need to be so careful as I did. The piezo disks are available in multiple diameters and I did find that the larger ones were a bit better at giving a signal from light impacts.

RobFarley

I'm using a thin plastic plate as a target (about 25cm diameter) so I reckon gluing it on there should work, I'll have a play!

Cheers, Rob

RobFarley

Great success!!

https://photos.app.goo.gl/xBSPqKwjELQqgwQ2A
Cheers, Rob

pert

Way cool! It looks very nice. Thanks for sharing an update.

RobFarley

Cheers, next on the list are lights...

Then a bigger display...

Then make a 6 target version
Cheers, Rob

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