Raspberry Pi Pico as AM Radio Transmitter
Building on the legacy of Raspberry Pis accidentally broadcasting FM, this post explores how the diminutive Raspberry Pi Pico can transmit AM radio. Leveraging the Pico's unique Programmable I/O (PIO) unit, the author demonstrates transmitting simple audio tones via On-Off Keying. It's a clever, low-level hardware hack that epitomizes the spirit of technical exploration popular on Hacker News.
The Lowdown
This article delves into the intriguing capability of the Raspberry Pi Pico to function as a low-power AM radio transmitter, building upon previous discoveries of regular Raspberry Pis emitting FM signals. The author explores the architectural differences and unique features of the Pico that make this possible, albeit with certain limitations.
- Older Raspberry Pis were found to unintentionally transmit FM radio using GPIO pins and software-controlled clocks, generating square waves that could be picked up by receivers.
- The Raspberry Pi Pico, with its distinct architecture, cannot achieve FM transmission in the same manner.
- However, the Pico's Programmable I/O (PIO) unit offers a powerful alternative, allowing independent, high-speed execution of minimal instruction sets to generate precise square waves.
- While complex amplitude modulation for arbitrary audio is not feasible with square waves, the Pico is well-suited for lower frequencies typical of AM radio (around 1000 KHz) using On-Off Keying (OOK).
- The author successfully demonstrates this by using PIO to generate a 1000 KHz carrier, which is then rapidly turned on and off to encode the 'Shave and A Haircut' melody.
- A basic AM radio can then pick up this OOK signal, effectively transmitting simple audio frequencies.
Through this project, the author showcases the surprising versatility and low-level control offered by the Raspberry Pi Pico's PIO, turning a general-purpose microcontroller into a basic radio transmitter with just a few lines of code and a wire antenna. It's a testament to creative hardware utilization, albeit with a reminder about potential regulatory implications for radio emissions.