Walkie talkie pin badge from the Detective Conan anime series using a custom PCB and an ATMEGA328P (Arduino) microcontroller. Integrated rechargable battery, battery lasts around 4-5 hours and can be charged in one hour using any USB-C cable.

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 indicating the circuit is powered, finally 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, maximum range is 100 meters in optimal conditions.

The battery lasts 4-5 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.

Technical description

This project uses the RF24Audio library (https://github.com/nRF24/RF24Audio) in a ATMEGA328P-AU chip, working at 3.3V 8MHz, you can load the program in a Arduino Pro Mini (3.3V 8Mhz version) and then solder the chip into the pcb, if the chip is brand new make sure to burn the Arduino Pro Mini bootloader.

The radio module I'm using is the NRF24L01 mini, which is a smaller version suitable for mounting on small pcb, to make it work I had to lower the transmission speed and the sampling rate of the audio.

Assembly instructions

1. Solder the NRF24L01 SMD module on the top right corner of the PCB, make sure the module is the SMD version since other module variants won't fit.
2. Solder the LiPo battery in the battery terminals located beneath the USB port, make sure the polarity is correct.
3. Program the board. You need to burn the bootloader for Arduino Pro mini (3.3V 8Mhz version), you can do it by using any AVR programmer or using another Arduino as a programmer. After burning the bootloader you can proceed and upload the program.