The further we progress into the digital age, the more traditional analog signal generation begins to seem like some long lost dark art. Even as a maker, it’s possible you’ve never used anything but digital signals in your projects. If that’s the case, looking at those analog waves of varying frequencies and amplitudes can seem overwhelming. But, the truth is that many of those signals are remarkably simple to create using modern technology.
If you’re curious about trying that out for yourself, Bitluni’s AM Radio Transmitter tutorial is a fantastic first step. If you’ve ever seen an amateur radio enthusiast’s workshop, you may think this will take a truckload of equipment and 30 foot radio antenna mast attached to the side of your house. Fortunately, that’s not necessary for this project—all you’ll need is an ESP32 and a single wire.
You won’t be able to transmit very far, but that wire is the antenna. The ESP32 has an onboard DAC (digital-to-analog converter) that will translate your code into an analog AM radio signal. AM (amplitude-modulation) radio works by modulating a high-frequency carrier signal, which is just a sine wave with a consistent amplitude.
As Bitluni shows on his oscilloscope in the video, the audio signal is applied to that carrier signal—the formula isn’t quite as simple as just multiplying them, but it’s close. The result is a wave pattern with varying amplitude, which is all an AM radio needs to pick up an audio transmission. To create that signal, Bitluni has provided both a converter for your audio clip and a sketch to use it on your ESP32.