You can build a Raspberry Pi retro radio with working physical knobs by pairing playback software with an audio output stage and choosing how the knobs are read. Use a rotary encoder for step-by-step station or playlist selection, or a potentiometer and an analog-to-digital converter (ADC) for a smooth dial. Neither setup automatically tunes real FM broadcasts: over-the-air reception requires a separate FM receiver.
Decide what the radio should play
Choose the source before buying parts, because a radio-shaped case and tuning dial do not determine whether the device receives radio broadcasts.
- Local audio: Play files stored on the Pi or attached storage. A dial can select playlists, genres, presets, or eras. The Raspberry Pi Official Magazine’s Time Machine Radio uses a song collection divided by decade; its tuning knob selects a decade rather than an RF frequency. Read the Time Machine Radio project description.
- Internet radio: Playback software can stream stations over a network. Adafruit’s WiFi radio guide describes this kind of build and lists a Pi, microSD card, suitable power supply, and headphones or amplified speakers as core requirements. Service availability and software requirements can change, so verify those for the service you choose. See Adafruit’s WiFi Radio guide.
- Actual FM reception: Add a receiver module and integrate its controls and audio with the Pi. This is a separate subsystem, not a feature provided by the Pi’s tuning knob alone. An Adafruit feature reports a clock-radio retrofit using an RDA5807 FM receiver controlled over I2C, an analog audio switch, and a TPA2016 amplifier; it is an example of an approach, not a complete verified parts recipe. Read the reported clock-radio retrofit.
Do not mistake an FM transmitter for a receiver. Adafruit’s PiPyPirate Radio uses an Si4713 to transmit the Pi’s audio to nearby FM radios; it does not receive FM broadcasts. See the PiPyPirate Radio project.
Choose how the tuning knob works
The two common control approaches feel and connect differently. Pick one based on the behavior you want, then check the selected board’s wiring and GPIO requirements.
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| Control | How it works | Good fit | Checks |
|---|---|---|---|
| Rotary encoder | Produces digital signals as the shaft turns. Software interprets movement as steps. | Next/previous station, preset, playlist, or menu selection. | Available GPIO pins, wiring and voltage compatibility, and the shaft and knob fit. |
| Potentiometer plus ADC | Changes an analog voltage as it turns. An ADC converts that position into values the Pi can read. | A smooth analog dial, position-based tuning scale, or volume control. | ADC compatibility, potentiometer range, wiring, and calibration. |
Encoder: step through choices
A rotary encoder is a digital input device. Each turn changes a count, which your software can map to a previous or next station, preset, or playlist. Some encoders also include a push switch that can be assigned to a separate action.
Raspberry Pi audio-board documentation describes GPIO 23 and 24 for encoder-based physical volume control in relevant configurations, and GPIO 27 for an encoder push switch. These are examples, not universal pin assignments: an audio board or another attached component may already use those pins. Check the Raspberry Pi audio HAT documentation.
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Potentiometer: make a smooth dial
A potentiometer acts as an adjustable voltage divider. A standard Raspberry Pi cannot directly read its changing analog voltage through an ordinary GPIO input, so the circuit needs an ADC. The Time Machine Radio project uses two potentiometers connected through an MCP3008: one controls volume and the other selects a music decade. See the documented project.
Software can turn the ADC reading into a volume level or divide the dial’s range into tuning positions. The cited project does not specify universal potentiometer resistance, wiring, or calibration thresholds. Select and validate those for your particular ADC and board rather than treating one set of values as suitable for every build.
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Select the Pi, audio hardware, and speaker together
The Pi runs playback and control software; the audio hardware provides a path to the speaker. A passive speaker needs a suitable amplifier or speaker output, so do not assume the Pi alone can drive it.
- Pi: The Pi Zero 2 W is used in the published Time Machine Radio build, making it one documented option—not a requirement for every radio. Confirm compatibility with the audio hardware and current availability before purchasing. See the Pi Zero 2 W project example.
- Audio HAT or amplifier: Raspberry Pi Codec Zero is a compact audio HAT with a mono mini-speaker driver rated at 1.2 W at 5 V into 8 ohms. The Time Machine Radio instead uses a Pimoroni Audio Amp SHIM with a built-in DAC. These are different designs, not assumed drop-in equivalents. Match the board to your speaker and follow its own power instructions. Review Raspberry Pi’s audio HAT specifications and setup guidance.
- Speaker: Check its impedance and power rating against the chosen output board. The Codec Zero specification above applies to that device and load; it should not be generalized to other audio boards.
Audio hardware can also occupy GPIO pins. Raspberry Pi’s documentation identifies power and ground, I2C pins 2 and 3, I2S pins 18–21, and—in relevant configurations—GPIO 23/24 for encoder control and GPIO 27 for a push switch. Make a pin plan for the exact board and attached devices before connecting controls. The same documentation notes that its HATs attach to the 40-pin GPIO header and are designed for Raspberry Pi OS plug-and-play through pre-programmed EEPROM; headless systems may need audio-device selection or configuration. DigiAMP+ is a specific exception to simple assumptions: it requires an external 12–24 V supply and is designed for Pi 3 and earlier, with a particular power arrangement detailed in its documentation. Check the exact audio-board instructions.
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Build and test in stages
- Define the behavior: Decide on local files, internet streams, or actual FM reception. Specify what the dial changes: stations, presets, playlists, decades, or another set of choices.
- Select a compatible Pi and audio route: Choose the board and audio output together, then confirm their power and compatibility requirements. The Pi Zero 2 W is a documented example, not a universal requirement.
- Choose the control hardware: Use an encoder for digital step changes. For an analog dial, pair a potentiometer with an ADC such as the MCP3008 used in the Time Machine Radio project.
- Plan GPIO use: List the pins required by the audio board, controls, and any other peripherals. Resolve conflicts before wiring; do not assign one pin to multiple functions.
- Match the speaker and supply: Check the speaker’s impedance and power rating against the audio output, and use the supply arrangement specified for the board.
- Bring up the electronics outside the case: Start the Pi, verify audio playback, then test knob readings and confirm that turns or positions select the intended items. The published project descriptions do not provide one universal ready-to-run software image for this exact combination of parts, so software configuration depends on your setup.
- Fit the hardware to the enclosure: Measure the control shaft, knob, speaker opening, mounting points, and ventilation for the particular donor radio or case. The documented Time Machine Radio description does not provide dimensions that apply to other enclosures.
Plan the software around the control
The control input only supplies a value or movement event; playback software must decide what that means. For an encoder, translate steps into a previous/next selection or preset change. For a potentiometer, read the ADC and map its range to a volume level or a set of dial positions. If selecting a different source interrupts playback, define when the new item starts and how volume changes behave.
The Time Machine Radio project describes a software loop that checks for a decade change, advances a song when appropriate, and pauses briefly between checks. That illustrates the basic pattern—read controls, update playback when needed, repeat—but it is not a universal software recipe for other boards or music libraries. Read the project’s software description.
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