Solar cells can easily provide enough power to operate a small radio receiver. This DIY Solar Powered Radioproject is an ideal set to take away on holiday. It covers the medium wave (AM) waveband, so why not laze on the beach this summer and listen to your favourite station. But first, let’s get busy with a little home construction. If you’ve already built some of the other circuits in our magazine then this one should be easy.
Fig – Solar Powered Radio
Solar Powered Radio – Here Comes the Sun
What we are using for this project is not just one solar cell, but a number connected to form a solar panel. On a very sunny day, it will give eight or nine volts at a current of over thirty milliamps (mA), but when the weather is not quite so bright the circuit will still work with less than two volts. The Sunny will happily work with any voltage in between, although the volume will be less when the solar cell is giving a lower voltage.
The Solar Powered Radio uses a type of circuit known as a Tuned Radio Frequency or TRF. If you look at the circuit diagram in Figure, you will see that it has a tuned circuit consisting of variable tuning capacitor VC1 and coil L1. You can make this coil yourself by winding about 35 turns of insulated wire onto a ferrite rod. The ferrite rod should be about 10cm long and 10mm or so in diameter.
Signals picked up by the tuned circuit are passed to IC1, which amplifies them and makes the signals louder. This little circuit is actually rather clever, because it will amplify a small signal more than a large one. This helps to make the volume more constant for stations of different strength, a feature known as automatic gain control (AGC). The chip also functions as a detector, converting the signal from radio to audio frequency.
Signals from IC1 are still not loud enough to drive a loudspeaker so we now have another circuit (IC2) known as an audio amplifier. This increases the sound signal voltage by up to 100 times, making it sufficient to drive the speaker LS1.
Simple to Build
Building the Solar Powered Radio is straightforward and doesn’t require advanced electronics skills. The circuit uses common components that are easy to work with, making it an excellent project for beginners and experienced builders alike.
The coil L1 is wound by hand using about 35 turns of thin insulated wire wrapped around a ferrite rod. The ferrite rod should be approximately 10 centimeters long and about 10 millimeters in diameter. This coil acts as the antenna system that picks up radio signals from the air.
When adding the resistors, double-check their values using the color bands or a multimeter to ensure accurate readings. The volume control connects to the circuit with three wires, and using different colored wires makes it much easier to keep track of the connections during assembly.
One of the most interesting features of this radio is that it doesn’t need an on/off switch. The circuit automatically starts working when enough sunlight hits the solar panel, and it shuts down naturally when the light fades. This makes it incredibly convenient for outdoor use, as you never have to worry about forgetting to turn it off and draining a battery.
Solar Powered Radio – Components List
Resistors – 0.25W or 0.5W 5% tolerance
- R1: 390Ω
- R2: 10kΩ
- RV1: 10k variable resistor (log)
Capacitors
- C1, C5: 10n ceramic
- C2: 220pF ceramic
- C3, C4: 470μF electrolytic (16V or 25V)
- C6: 100μF electrolytic (10V)
- VC1: 365pF 2-section variable capacitor
Semiconductors
The beauty of this Solar Powered Radio project lies in its simplicity and practicality. Once built, you’ll have a completely self-contained radio that runs entirely on solar power, making it perfect for outdoor adventures, beach trips, or simply as an interesting conversation piece that demonstrates the power of renewable energy in electronics.
The automatic gain control feature means you won’t need to constantly adjust the volume as you tune between different stations, and the lack of an on/off switch means the radio will automatically come to life whenever there’s sufficient sunlight hitting the solar panel. It’s a perfect introduction to both radio electronics and solar power applications.