McNugget Receiver

How I turned a McDonald's toy into a satellite receiver!

Background

According to this report:

Recently, McDonald’s kicked off a series of activities ahead of Children’s Day on 1 June, focusing on their classic McNuggets. The fast-food chain launched a special offer of 20 McNuggets for 20 RMB and a variety of limited edition ‘Walkie-Talkie’ toys. The ‘Walkie-Talkie’ is designed in the style of the classic McNuggets and fries. Users can also buy a ‘Walkie-Talkie’ and a graffiti sticker for an additional 38 RMB. On 22 May, the McDonald’s ‘Walkie-Talkie’ toy went on sale, causing the restaurant’s app to crash.

The McNuggets and fries toy walkie-talkies are really cute. They can transmit and receive FM signals at 409.9 MHz, which is a public, license-free walkie-talkie frequency.

I managed to get one on May 22, 2024, immediately after McDonald’s released the toy offer. I rushed to the nearest store and bought 20 McNuggets so I could be eligible to buy the toys.

McDonald's McNuggets and fries toy walkie-talkies.

As a ham and an engineer, I naturally disassembled them.

The teardown details of McDonald's toy walkie-talkies.

Then I discovered that the RF IC inside the toy is a BK4802, which can be operated at 430-440MHz. This range covers both local amateur radio FM repeaters, and several well-known satellite FM repeaters, including ARISS, the TEVEL series, and SO-50.

So, an idea came to mind: what if I could modify the firmware of these toy walkie-talkies to make them capable of receiving signals from satellites?

Demo Showcase!

🛰️ RS-40S (UmKA 1) SSTV signal received by McNugget Receiver. Try to decode it!
🛰️ FM repeater at International Space Station received by McNugget Receiver.

How I Made It

To start with, I disassembled the toy walkie-talkies.

I disassembled the toy walkie-talkies.

Then, I used a multimeter to measure the connectivity of each pad on the circuit board. This helped me to eventually draw the circuit diagram of the toy walkie-talkie.

Draw the circuit diagram of the toy walkie-talkie using a multimeter.
The circuit diagram of the McDonald's toy walkie-talkie.

After analyzing the circuit, I decided to remove the original MCU, and connect those I/Os to a new programmable MCU, where I could design and write new firmware to change the RX frequency.

I decide to remove the original MCU.
Then connect those I/Os to a new programmable MCU.

Next, I bypassed the original filter behind the antenna since its working frequency was not suitable for satellite frequencies. I also replaced the original antenna with a 50-ohm coaxial cable, allowing for the future connection of a more powerful antenna.

Board Connections: The red wire bypasses the original filter.

After modifying the circuit, it was time for the embedded part. So, I wrote the firmware for the STM32F042K6T6, a new MCU that handles all functions.

Me, writing the new firmware in my studio.
Developing the STM32F042K6T6 firmware using STM32CubeMX and Keil UV5.

After several rounds of testing and bug fixing, I finally made it work. Hooray! 🎉

I’ve open-sourced the entire project, so you can make your own McNuggets Receiver as well.

Please consider adding a reaction below, and star the project on GitHub if you like it!