Keychain Remote Control Sound Player

I needed to play sound clips for a Halloween costume, and for a historic house docent project. This device allows you to use a keychain remote and play MP3 sound effects or music. The remote can be hidden so the sounds become a fun part of the act.

The basic setup is that the keychain remote controls a board with relays. The MP3 player board has input pins that play a corresponding sound when pulled low. So you just connect the relays to the MP3 board and then the keychain remote will play a different sound for each button. You could get a lot fancier than this with an Arduino etc. in the middle too.

[Note - some of the links below are affiliate links to help pay for these projects, though no money has been received to date :-)]

1. Keychain with remote relay. I used a 4 channel one, but there are remotes with different numbers of buttons/relays. The way I have it setup, each keychain button plays one sound. So, I can play 4 different sounds/songs. The MP3 board has 8 input trigger pins, so that is the max with this simple approach if you had an 8 button remote. Some of the relay boards are 12V only, some are 24V, and some are 5V-80V. The latter is easier since you only need a single 5V (USB) battery to supply both the relay board and audio player board. The 12V ones are common, and I have used them with a combined 12V & 5V battery.
2. MP3 Sound board. You can plug these into your computer via micro USB to transfer MP3 files. Some have built-in memory, and some use a separate micro SD card.
3. Speaker - 5W, 4 Ohm. The MP3 boards have a small onboard amplifier. You could also use an amplified speaker since the board has both a soldered amplified speaker output and a 3.5mm mini phono phono output.
4. Speaker connector wires (optional). I used a connector on the speaker so I can remove it from the audio board as needed (both the speaker and audio board are solder connectors). I used 2 pin JST SM connectors with wires attached, but any 2 pin connector is fine.
5. 12V + USB battery. Some keychain remotes/relays use 12V, and the MP3 board uses 5V. You could use a voltage converter to go from 5V to 12V, or vice versa. Or a battery that supplies both 5V and 12V like this one. Or, a keychain remote relay board that supports 5V-80V is easier to use. Having 5V only conveniently allows any USB battery to be used. Important: Most USB batteries will shut off automatically if they do not detect a load, and I tested a few with this MP3 board + relay board. All the USB batteries turned off in about a minute. So, the TalentCell battery is recommended since it has a switch to turn on and off - that on/off switch is the key feature, or a USB batttery that stays on.
6. USB solder connector This is to connect the battery to the relay and MP3 board. There are also USB Type C solder connectors. There are also USB screw terminals, but they take up a bit more space.
7. 5.5mm x 2.1mm Terminal Connector This is only needed if you use a 12V remote relay board. The 5V USB connector is used for the MP3 board, and the 12V output via this screw terminal is used for the relay board. A pig-tailed connector is probably fine too.
8. 10mm Heat Shrink Tubing I used this on the USB connector to save room over the included housings.
9. Wire: I used some 28 AWG silicone wire and some 26 AWG silicone wire for the power connector.
10. Screws for mounting the components. Since I 3D printed the case, I used M2x6mm screws with washer heads to hold the components in the case. Ones without the washer heads may work better in tighter locations - I have sometimes used a mix on the same board since some holes have more clearance than others. 8mm long ones may be good as a backup if you strip any threads. FWIW, the M2x8mm washer head self threading screws are what often come with hobby servo motors.

Each keychain / relay system is a bit different. You may need to pair the keychain with the relay board by powering the board, then pressing the button once. The mode I used was a momentary one - the relay connects while the remote button is pressed, and the relay disconnects when the remote button is released. That has been the default mode for the ones I tried.

The MP3 player board has a lot of capabilities.

To load the sounds/songs, some have built-in memory, and some use a micro SD card. Both can plug into a PC to manage the files, and the one with the micro SD card can also be managed with just the card - either way works. The filenames are 00001.mpg, 00002.mpg, 00003.mpg, 00004.mpg...

I just used 4 sounds - one for each button. With a microprocessor you could get fancy with two sequential button codes or something to allow more. There are also MP3 boards that only have a serial interface.

For the simple mode, there are 8 IO pins to play up to 8 MP3 files. If you connect one IO pin to ground, it will play the corresponding MP3 file. There are various modes you can set for playback control - I just used the play to end, and allow interruptions mode. It is called the "IO Independent Mode 0" and the corresponding dip switches are off-on-off.

There is a serial mode that can play up to 255 sounds if you want to use an Arduino etc.

The box I designed holds the particular battery I used, so that may need to be adjusted for the battery you choose. Also, note that the battery I used may have changed size slightly in newer versions - wider version attached.

This box uses a snap fit lid, and posts for the component stand offs. I printed it in PLA+.

The Adafruit snap fit lid YouTube video was so helpful! Be sure to read the comments (from TeleToyland) on the one step that needs a particular setting

The "wider" version of the files just has a 5mm wider battery compartment since TalentCell changed the battery width slightly recently.

For the battery connector, I used a solder USB Type A connector. The outer two pins are + and -, so check with a meter or look it up to make sure you know which is which. I used a sharpie to mark those on the connector. The easiest way to solder these is to tin the wires and the outer two pins, then solder them together. I used about 20mm of 10mm clear heat shrink tubing to cover the wires, and did not use the housing since it was in the way. The heat shrink can't go too far down the connector so it fits in the battery. If you redesigned the box, the USB connector cover could fit. There are also USB Type C solder connectors if you prefer that for your battery.

For one version I did with a 12V relay, I used a battery that supplies both 12V and 5V, and used a 5.5mmx2.1mm screw terminal for the 12V side.

For the 5W, 4 Ohm speaker, I soldered the pin side of the JST SM connector on the speaker.

For the MP3 player board, I laid out the board, battery, and relay to gauge the wire lengths. Solder red and black wires on the power pins. Solder orange, yellow, green, and blue wires on the IO pins 0-3. I had those colors, but any color is fine. Solder the JST SM socket connector to the speaker pins.

The MP3 player board also has a line out using a 3.5mm mini phono jack. That works really well with a powered speaker, but I preferred the enclosed battery for the costume application.

The speak connector uses a built in amp, so you can turn the small potentiometer on the board to adjust the volume.

The rest of the connections are to the relay board and use a screwdriver. The battery and MP3 board are connected to the Vcc terminal. The battery, MP3, and the closest COM terminal are connected the the Gnd Pin. That COM terminal is daisy-chain connected to all four of the COM terminals.

With all the connections made, you can test the system out before mounting in the box.