Sound grenade

[Christopheros]

Hi,

Maybe this question is not really relevant, but I really want to build an airsoft grenade that has a tini but loud loudspeaker, a little sound board and some storage (sd card) for the BOOM sound and it would play the sound like the real ones work. Could you electrician guys help me out, what kind of stuff do I really need that fits in the grenade shell and works?

 

Thanks guys

[KeyboardCowboy]

On 7/30/2019 at 4:32 PM, Christopheros said:

Hi,

Maybe this question is not really relevant, but I really want to build an airsoft grenade that has a tini but loud loudspeaker, a little sound board and some storage (sd card) for the BOOM sound and it would play the sound like the real ones work. Could you electrician guys help me out, what kind of stuff do I really need that fits in the grenade shell and works?

 

Thanks guys

Yes! who wouldn't want that? umm, I would start calling it a DSD (deployable sound device), people tend to frown upon things like 'grenade', 'prop bomb', or 'mock nuke'. Side note, I wouldn't ask for an 'electrician', we are engineers of an electronic nature.

 

So while doing some research on your behalf, ya got problems....

- Your not going to be able to fit much into a standard pineapple grenade 'casing?'.... now If you sliced the puppy down the middle, ya might.

- You could always 3d print a grenade shaped housing for the guts

- Your sound to size ratio needs some attention. A big sound requires a big power source. So you could play a media file from... idk a pi or arduino or something, but your max volume would leave much to be desired. (I'm assuming you want something small) I just cant see a small lipo being able to put out what ya need.

- You could however compromise, a loud high pitched chirp could serve as your 'boom' noise, the high frequency would carry nice.

Something like this maybe, ' 100dB @ 3V, 10cm ', typical draw is 9 mA, so battery power is well within the realm of possible.

Spoiler

https://www.digikey.com/product-detail/en/pui-audio-inc/AI-3035-TWT-3V-R/668-1204-ND/1745457

I'm sure somebody could recommend a better one.

- I'm more of a fan of cylinder type DSD's, you could fit an 'arm' button and a power switch on it nicely, mount your buzzer near the top, weigh the bottom down and bam, DSD.

 

Something as simple as the above could be hacked together with a small Arduino like board, I would recommend the 'Adafruit Feather 32u4 Basic Proto', it has a built in lipo charger and its programmable over usb, it just make things so much easier.

[mariushm]

Find a cheap MP3 player that defaults on music playback when you power it on, so just hitting the play button would start to play a song.

For example, one of those USB stick players like this:

https://www.amazon.com/Start-Player-Digital-Support-Black/dp/B06XG8CXP6/

https://www.amazon.com/Player-Tuscom-Portable-Support-Lovers/dp/B07N7PP4VK/

 

You can load a single mp3 track into the memory, optionally with some amount of silence at the beginning, let's say 5 seconds.

You could either have the mp3 player directly on one side of the grenade with the buttons accessible, or you could open the case and solder wires to the two wires for the play button and two wires for the on/off switch and only place these two (switch + momentary button) on one side of the grenade - you could call it  arm grenade (on switch) and release safety switch (for play button)

Alternatively, you could add a microcontroller inside the grenade (an arduino or any microcontroller, i'll just say arduino from now on for simplicity) that's powered from same power you have for the mp3 player - when you hit the switch on the grenade, the arduino powers up. From this point, either wait a few seconds and then hit play with the arduino, or hit play right away relying on the seconds of silence.

When you hit play on the mp3 player what happens is that the button has a metalic surface under the plastic which makes contact with two wires on the circuit board, so you basically short out those wires for the period the button is pushed down.

So you can use a simple 5v relay to create the connection between those two wires on the circuit board using your Arduino.

Alternatively, you can go further and determine what actually happens when you short the two wires. Typically, one of the wires is connected either to the voltage (battery or 5v) or ground ... when you make the short with the button, the wire from the processor either is connected to ground or is connected to power, and the cpu detects this change of state and acts accordingly.

You can do this with arduino, you can either send some voltage to the wire going to the cpu, which makes the cpu think you pressed the play button, or you can actually connect that wire to ground if the player is designed that way)

 

Ok .. so now you got your start music sorted... now you just need to amplify that music and hear it.

 

You can get tiny audio amplifiers from ebay or various stores

Here's one of the cheapest and easiest to use:

 

1. https://www.ebay.com/itm/PAM8403-2X3W-Mini-Audio-Class-D-amplifier-board-2-5-5V-input-ECER-LL/192930593389

2. https://www.ebay.com/itm/PAM8403-2X3W-Mini-Audio-Class-D-amplifier-board-2-5-5V-input-ECER-Hn/123819049977

3. https://www.ebay.com/itm/2015-Digital-DC-5V-Amplifier-Board-Class-D-2-3W-USB-PAM8403-Audio-Module-BB-SP/153553100763?epid=1853288910

 

These will give you up to 6 watts of audio, depending on input voltage, and the board can handle up to 5v (you could power it using 3 AA alkaline batteries or directly from the tiny mp3 player battery (which should be 3.7..4.2v lithium).

 

You basically get a regular stereo cable to 2 x RCA extension like this one: 

1. https://www.ebay.com/itm/3-5mm-to-2-RCA-Stereo-Audio-Cable-Male-Jack-for-Ipod-MP3-1-2M-U5H5/262977006678

 

Why this kind? Well, doesn't have to be this kind, but these ones separate the 3 wires (left, right, ground from the stereo jack into  left+ground and right+ground so you can just cut the rca connectors and solder the wires into the tiny amplifier board... and you can also easily cut the length of the wires to make the cable smaller.

 

Now all that's left is to get one or two speakers and connect those to the amplifier board... aim for  ~4 ohm speakers, which are tweeters or general, not woofers, bass etc

 

Here's a whole lot of them... i pre-filtered the list to show only 3 ohm ... 8 ohm speakers : https://www.digikey.com/short/pbd42d

The list is sorted by price and cheapest will be 8 ohm ... look for closest to 4 ohm and maybe aim for 2-3 watts as that's the most the amplifier can do.

ex: https://www.digikey.com/product-detail/en/pui-audio-inc/AS04004PO-2-R/668-1234-ND/1745528

 

or something like this, that can do max 8kHz but tiny package: https://www.digikey.com/product-detail/en/soberton-inc/E-3304/433-1176-ND/8021826