Solar FM Radio

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Introduction: Solar FM Radio

About: I am a graduate student in conservation biology at Clemson University. When I'm not studying in the library or out in the field collecting data, I love designing and building DIY projects!

This solar powered FM radio has a 3D printed enclosure and a vintage design inspired by tabletop radios of the 1940's. Here's the tools and supplies you'll need to build one:

3D printed components:

  • Enclosure body
  • Front panel
  • LED badge
  • Tuning and volume knobs

Other components:

Tools:

  • Soldering iron and solder
  • Holt glue gun and gluesticks
  • Two part quick set epoxy
  • Scissors
  • Multimeter (optional)
  • 3D printer with PLA (minimum bed size: 220 x 220 x 140)

Step 1: The Receiver Board

The heart of this project is the IC-Station FM receiver module. It's a single board FM band receiver with dual LTK 5128 class D amplifier circuits (90% efficiency and 10% THD). There are many versions of this board on Amazon and eBay. I've tried a few of them and the version from IC-Station seems to be the most reliable.

The audio signal is output to either a 3.5mm jack or through the speaker output pins. Plugging in an auxiliary cable or headphones will automatically switch the output from the speaker(s) to the jack. The output from the pins is 3 watts per channel at 4 Ohms (50-18,000 Hz). There are breakout pins that allow the module to be used as a mono or stereo amplifier. When the pins are bridged, stereo sound is sent to each speaker output independently.

The module is controlled by two digital rotary encoders, one with 30 point volume control and the other with 0.1 MHz tuning. A backlit LCD display shows the volume level, current station, and signal strength.

The board can be powered through a micro USB input or by soldering to the DC input pins. The input voltage range is 3 - 5v, and the board has an auto shutdown feature at 3.0v that keeps connected batteries from being over-discharged.

There is a pin on the top of the board for attaching a wire antennae which can be internal or external. For this project I used a 75cm long wire (1/4 wavelength at 98 MHz, which is in the middle of the FM frequency band).

Step 2: The Other Components

TP4056 lithium battery charger with protection:

The TP4056 is a simple linear charger for single cell lithium ion batteries. The MakerFocus board has additional protection circuitry for over-charging (4.2v), over-discharging (2.5v), and over-current (3a). The input is 4.5 - 5.5v and the charging current is determined by the input, with a 1a maximum. For this project, I paired the charger with a single 18650 LG M29 lithium ion battery, but a wide range of lithium batteries are compatible with the TP4056.

Uxcell 1 watt solar panel:

The solar panel in this project produces 6v open / 5.2v load at about 180mAh in full sunlight. I used an inline diode to keep the panel from draining the battery in cloudy conditions. The diode drops the voltage to about 4.5v which is perfect for the TP4056.

Dayton Audio CE65W-8 full range driver:

I chose a small Dayton Audio full range driver for this project. It has a 2.5" woven glass fibre cone and a rubber surround. The relatively low power handling, 7w RMS at 8 Ohms, works well with the low power output from the receiver module. The specs below were used to calculate the enclosure volume:

  • Frequency response: 105-16,000 Hz
  • Sensitivity: 83 db
  • Resonant frequency (Fs): 105 Hz
  • Driver equivalent volume (Vas): 0.002 ft3
  • total Q (Qts): 0.99

Step 3: The 3D Printed Enclosure

The enclosure for this project is 3D printed in two parts, the main body and a front panel. The front panel is designed to fit into a pocket (rabbet joint) in the main body.

The body is 220 x 115 x 140mm with 6mm thick walls. The solar panel fits flush into an inset in the top of the radio and the power switch is centered on the back. The body should be printed vertically with the back of the radio against the printer bed.

The front panel is 214 x 109 x 3mm with a 62mm through hole for the rear mounted driver. There are also through holes for the LCD display, rotary encoders, and the panel mount LED.

The other 3D printed components include the volume and tuning knobs, the LED badge, and any additional decor pieces like the speaker accent ring (see step 10).

I've included .stl files for all the parts below. I've also attached a model of the FM receiver module that can be used to create through holes for the LCD and rotary encoders if you'd like to design your own radio.

I sliced the parts in Cura 4.3 using the following settings:

  • 0.25mm layer height
  • 60mm/s print speed
  • 20% grid infill
  • skirt style bed adhesion
  • support generation enabled for the main body (not needed for the other parts)

I printed the parts on a Lulzbot TAZ 6 in PLA. The minimum bed size for the prints is 220 x 220 x 140mm. The main body takes approximately 20 hours and uses 350g of material. The front panel takes approximately 5 hours and uses 67g. The knobs and badge take less than an hour and use 7g. I used a 205c nozzle and 60c bed temperature.

The internal volume of the enclosure is approximately 3L, which yields an F3 of 83 Hz with the Dayton Audio driver. I added about 15g of well dispersed polyfill to give the radio a more full sound. This step is optional, and the radio still sounds fine without any padding.

Step 4: The Wiring Diagram

There are two wiring diagrams above: one for the power assembly and one for the FM receiver module. All the connections are labelled as they are on the boards. Notice the orientation of the diode in the diagram (the gray end points towards the TP4056). If you build the radio with a single driver, remember to bridge the mono/stereo pins on the back of the radio module.

Step 5: The Power Source

The power assembly is made of 4 components: the solar panel, TP4056 charging board, battery, and power switch. Make sure the wires for the solar panel are long enough to reach the charging board in the enclosure.

The TP4056 has two onboard LEDs, a red one that indicates when the battery is charging and a green one that indicates when the battery is fully charged. These can be extended to the exterior of the enclosure if you have good soldering skills (the soldering pads are very small).

Step 6: The Front Panel

The LCD display on the radio module is recessed from the back of the rotary encoders. I used a 3mm thick piece of clear acrylic in between the display and the front panel to remove the gap and also keep the enclosure sealed for sound quality. I cut a 40 x 50mm piece and attached it to the back of the panel using hot glue.

The radio module is attached by threading the included nuts onto the rotary encoder shafts. Once tight, the board is firmly in place and no additional attachments are necessary.

The driver is rear mounted on the back of the panel. Because of its weight, I centered the driver using hot glue and then added epoxy around the frame to ensure that it was solidly attached to the panel.

Step 7: The Enclosure Body

The power switch is attached to the back of the main body using the included nut. I also added a bit of hot glue on the inside to ensure it wouldn't loosen over time.

The solar panel sits flush with the top of the main body and is held in place with epoxy.

I used hot glue to attach the TP4056 charging board and the battery inside the main body. The placement of the parts isn't super important as long as the wires reach. I also added a bit of glue to the battery to make sure it would stay in the battery holder.

Step 8: The Power LED and Badge

The power LED is mounted in a panel mount holder that has a threaded shaft. The 3D printed badge is pushed onto the LED holder which is then mounted into the front panel using the included nut. I added a little hot glue to the LED and holder to make sure everything would stay in place.

The forward voltage from the radio module is about 2.5v, which is low enough to connect a 5mm LED directly to the board. I added a 2k Ohm resistor inline to the LED to reduce the brightness.

Step 9: The Final Assembly

Once all the components are soldered together the radio can be tested. First place the solar panel in direct sunlight or under a high intensity artificial light and make sure that the red charging indicator on the TP4056 lights up; this indicates that the solar panel can charge the battery.

Next, flip the power switch and the radio should begin to play. This indicates that the switch is functional, the receiver board is receiving power, and the driver is wired properly. The power LED should also turn off and on with the radio board.

Turn the volume and tuning knobs and ensure that they are both functional and that the LCD display changes accordingly.

If everything works the way it should, then the radio is ready for final assembly. If you choose to add polyfill to the enclosure, make sure it is "fluffed up" and well dispersed. Adding too much will make the radio sound muffled and reduce lower frequencies. The front panel is glued into the main body using epoxy. If the front panel doesn't sit perfectly flush, add some weight to the middle of the panel until the epoxy sets. Clean up excess epoxy using a damp rag or paper towel.

I put a drop of epoxy on the top of the rotary encoders and then pressed the 3D printed knobs in place. Make sure the knobs are level and that no epoxy comes into contact with the base of the rotary encoders.

Step 10: Additional Parts and Customization

This project is designed around specific components, but it can be modified in many ways to suit your own design ideas. The .stl files for the printed parts can be opened and modified using almost any design software, including TinkerCAD, which is available online for free. For example, Once I finished building the radio, I designed a speaker grille (file attached below) that I attached to the front panel using epoxy. Here are some other design ideas:

  • The receiver board can power many small drivers, and can also power two drivers if you want to make a stereo radio.
  • The solar panel in the top of the enclosure can be replaced with a panel of different shape or size.
  • The speaker grille or LED badge can be redesigned to fit your own design ideas.
  • The internal wire antennae can be replaced with an external wire or telescoping antennae to improve reception.
  • The battery can be replaced with a larger cell or multiple cells in parallel to increase run time.

If you have any questions or ideas, feel free to leave a comment at the bottom of the page. Thanks for reading, and good luck building!

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