Annual 2025 Contest: Home-Grown Software AM Radio Transmitter
In a fascinating twist, hobbyists have found a fun and achievable way to generate an AM radio signal using minimal components. This method, demonstrated using an ATTiny85 microcontroller, involves synthesizing a high-frequency carrier signal directly from one of its output pins, then modulating it to play audio or simple tones.
The process is quite straightforward. First, an ATTiny85 output pin is configured to toggle at the desired RF frequency, typically around 1 MHz. Next, code is written to switch the carrier signal on and off at audio rates, encoding AM signals that correspond to sound or melodies. Finally, a simple antenna, such as a length of wire, is attached to the output pin to radiate the AM signal.
This method produces a low-power signal that can be received by a standard AM radio tuned to the carrier frequency. It's important to note that the ATTiny85's timer and GPIO peripherals are used to synthesize the RF signal entirely in software.
While more advanced microcontrollers like ESP8266 or ESP32 can generate complex modulation schemes, the ATTiny85 example is simple and effective for basic AM transmission within the broadcast band.
To build your own software-only AM transmitter, follow these key steps:
- Configure an ATTiny85 output pin to toggle at the desired RF frequency (e.g., ~1 MHz).
- Write code to switch the carrier signal on and off at audio rates to encode AM signals.
- Attach a simple antenna (like a length of wire) to the output pin.
- Upload the code and power the microcontroller.
For a more detailed guide, including code explanations and demonstrations, check out project summaries from Hackaday and Instagram posts documenting these software-only transmitters with the ATTiny85.
One notable entry to the 2025 One-Hertz Challenge was from a hobbyist known as [oldradiofixer], who set up the microcontroller to toggle pin PB0 at 1 MHz to create an RF carrier. This transmitter played a simple melody, specifically the Twilight Zone theme, on any old radio. The melody repeats every second, making it a valid entry to the challenge.
A video demonstration of the transmitter's functioning is available to illustrate the ease of generating a broadcast AM signal with minimal components. Watch as the ATTiny85 outputs an AM radio signal in the broadcast band, playing a recognizable tune that can be picked up by any nearby AM radio.
In conclusion, with a bit of software and a length of wire, you too can join the ranks of hobbyists generating AM radio signals. Give it a try and let the sounds of the Twilight Zone fill the airwaves!
- The Twilight Zone theme can be heard on an old radio when the ATTiny85 microcontroller, configured to toggle pin PB0 at 1 MHz, generates an AM radio signal within the broadcast band, demonstrating the potential of using technology to create simple AM transmitters.
- A length of wire, acting as an antenna, radiates the AM signal produced by the ATTiny85 microcontroller's software-only AM transmitter, showcasing the effective use of minimal components to generate a recognizable broadcast AM signal.
