DIY Solar Powered Pocket Radio

In this Instructables post, we will be building a solar-powered pocket-sized radio. The new design for this radio is inspired by designs from Sanyo RP-AMT2 in the 1980s. However, the old version had a relatively small solar cell, so it was less efficient than the possibilities today. Our modern take on a old concept uses a high efficiency satellite solar cell that puts out 2.5Voc, 1 Isc and limited by the e-peas controller at 110mA, so that ~1 hour of solar exposure can play ~4 hours of audio with 25mA consumption. Fully charged the radio can run for ~38 hours without any sunlight.

If you are interested in learning more this particular design or the history of solar radios, I'm currently pursuing a masters degree in Solar Energy Engineering and would be more than happy help answer your questions.

Parts List:

• Solar Cell: This example uses a discontinued Tecstar Satellite solar cell, but any solar cell 2.5x1.75inch (65x45mm) or smaller and under 5 volts open circuit will work. Powerfilm or AnySolar are good options and are generally robust from breakage.
• Controller: Epeas controller (and more on the chips here)
• Radio: Micro FM radio
• Battery: EEMB Lithium Polymer Battery, 3.7V 950mA
• Enclosure: Clear SLA 3D printing
• Connector: JST-PH 2.0 Female connector
• Fasteners: Tiny Screws, quantity 8, 1.7mmx5mm

Tools Required:

• Soldering iron
• Solder lead free with flux
• Wire, 30 awg, 300mm length
• Hot glue gun or other clear adhesive

How it works:

The key component is the Epeas Solar Energy Harvester, which acts as the controller and handles the battery charging, maximum power point tracking, and has two regulated voltage outputs, making the setup of the radio a breeze while also being able to sip every photon and put it into the battery. The radio module is a digital micro FM receiver from 70-108MHz and uses 25mA at 1.8-3.6V. The cord for the headphones acts as the antenna for the radio.

The first step is to either order or print the enclosure for the radio and acquire the rest of the parts. The case was designed in Fusion 360 and can be modified from the original file. Otherwise, the STL files are also included. Please note, parts may fit differently depending on your printer calibration.

For the enclosure, the clearer the better to allow sunlight to interact with the solar panel. So, if you have access or can order a transparent SLA 3D print that will produce the best result for power output. This design will also work with FDM clear filament but you may have a reduced power output and you won't be able to see all of the internal electronics.

While some of the components use larger gauge wire, using 30 awg for all of the components is recommended due to space constraints inside the radio.

For the first step, solder the two 50mm wires for the radio receiver and the other two ends onto the VHC (3.3 volt output) and the ground (GND) connection.

Next, solder the JST-PH 2.0 connector onto the battery (BAT) + connection and adjacent ground (GND) connection. If you have a lithium battery with a smaller connector that will make it easier to place inside the case and is recommend.

Third, is to solder on the leads to the solar cell. Various solar cells will work for this application. They will just need to be under 5 volts open circuit voltage. So, when in full sun with no load, the reading should be under 5v with your multimeter. The solar cell will be soldered onto the source (SRC) connection for positive (+) terminal and the adjacent ground (-) negative for the other solar cell connection.

The next step is to insert the components into the plastic case. The components are partially held in with the design of the case but a bit of hot glue or other clear adhesive can be used to assist in holding the radio module and EPeas controller.

The final step is to attach the battery to the back cover, insert the battery and screw down the 4 screws around the top of the battery case. Then, plug in the battery to the JST connector and insert the battery, wiring into the case. Be careful not to put additional pressure when inserting the battery and wires into the case to avoid cracking the solar cells (like I did)

The last step is putting it in the sun! In order to use it, you'll need to charge up the battery. While this will charge in room light, it's best to charge in full brightness due to the low start voltage of the e-peas solar controller.

Tune in to your favorite radio station, plug in some headphones and enjoy!