Detective Boys walkie talkie pin badge

Details

I designed a walkie talkie radio pin badge inspired by Detective Conan anime series using a custom PCB and an ATMEGA328P (Arduino) microcontroller. Integrated rechargable battery, can be charged using any USB-C cable and USB power supply. Thanks to the RF24Audio library I could manage to send the audio using NRF24L01 modules easily with minimal configuration and adjustments.

Easy to use, just plug a headphone pair and press the button to talk to nearby pin badges !

How to use

To use the walkie talkie plug any headphones with microphone into the 3.5mm audio jack, then flick the switch on the left side of the board and the LED will light up. Press and hold the button on the board to transmit audio, all the near walkie talkies will receive and play the audio. No pairing or previous configuration is needed.

The battery lasts around 4 hours and it can be recharged by plugging an USB-C cable, any cable or power source is compatible. When the battery is charging, the LED near the USB connector will light up, when the battery is fully charged the LED will turn off again. The headphones used may affect on the audio quality, try using different headphones to compare the results.

Technical description

This project uses ATMEGA328P microcontroller on a custom PCB, the microcontrollers sends the audio data using NRF24L01 radio modules, ATMEGA328P microcontroller works at 3.3V 8MHz, you can program it using Arduino IDE and an external programmer like USBTinyISP.

The NRF24L01 radio module is a SMD version suitable for small sized boards, it has a maximum range of 100 meters.

The LiPo battery is directly soldered into the battery terminals of the board, recommended capacity is 100-150mAh.

Some improvements to be made

The short range is the principal handicap of this project, using small and cheap NRF4L01 modules in a board that can fit in the palm of your hand really limits the transmit power of the device, best range I could get was about 30 meters, replacing the modules with bigger ones (with antenna) would probably increase that number.

Audio quality is fine, not great but enough to communicate, quality depends on the microphone that the headphone pair has, so I got different results every time.

Files

DETECTIVE BOYS BADGE V1.2.pdf

Circuit PDF schematic

Adobe Portable Document Format - 82.05 kB - 06/21/2023 at 16:46

Preview

KiCad PCB Files.rar

Circuit board project files made with KiCad, contains all necessary fabrication files to order the PCB on any PCB manufacturer

RAR Archive - 5.72 MB - 06/21/2023 at 16:22

Download

Arduino Code.rar

Code for ATMEGA328P made in Arduino IDE, uses RF24Audio library

RAR Archive - 86.71 kB - 06/21/2023 at 16:22

Download

Components

1 × Custom circuit board Custom PCB with ATMEGA328P microcontroller, audio preamp circuit and USB-C charging port

1 × Lipo battery 100mAh Tiny lithium-polimer battery to power the circuit, capacity should be 100mAh or greater

1 × NRF24L01 SMD module NRF24L01 radio module (mini surface mount version)

Build Instructions

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Order the pre-assembled circuit board

The first step is to order the main circuit board, for doing this you have two options:

The first one is to download the fabrication files from the github folder and manually order the assembled boards on any PCB manufacturer, the github page contains all necessary files for the board fabrication and assembly (gerbers, bill of materials and pick and place), I recommend ordering at JLCPCB since all the components I selected are provided from them.

The second option is to order the assembled board from PCBWay, I uploaded a project on PCBWay with all the fabrication files and board configuration already done, so you don't have to worry about it.

Solder the NRF24L01 radio module

You can get the NRF24L01 modules on websites like Aliexpress or Amazon, make sure the module version is the SMD version, since this one will fit on the board footprint.

On the top right corner of the board you must solder the 8 pins of the NRF24L01 smd module, you can you preferred soldering tool, just make sure there are no solder bridges and all pads are connected afterwards.

Solder the LiPo battery

You will need a Lipo battery with 100mAh capacity, you can get a higher capacity one but take into account that more capacity means a bigger battery so it won't fit into the board, the battery must have a protection circuit included.

The battery must be soldered on the "BAT" connector placed below the USB charging port, I recommend using a soldering iron with an small tip, please be careful with the polarity as you could damage the whole board !

After soldering, flick the switch on the left side of the board to turn on the circuit, the red LED on the left side should light up indicating everything is OK.

Discussions

Detective Boys walkie talkie pin badge

Details

How to use

Technical description