Solar cell instead of a microphone

Under the influence of light on a silicon solar cell, a photovoltaic effect occurs — voltage or electrical current appears. This phenomenon is generally used for receiving electricity, but now we are going to talk about how, with the help of a solar cell and headphones, we will make an elementary flicker indicator that reveals low-quality light bulbs.

For the experiment, we took a small fraction of a solar cell from waste products from a nominal voltage of 0.5 volts and power of 0.25 Watt. Of course, this is not the most appropriate option, as this cell has neither a pad nor a protective coating, and is therefore very fragile. In addition, it has no wire leads, so we had to solder contacts directly on the front and back of the panel. If you want to use the appliance for a long time, it is better to buy a ready-made solar panel or take it from a garden lantern.

To the pins on the solar panel we soldered the mini-jack headphone input: left and right channels — at one pole of the solar panel, «earth» — on the other. It remains to plug in the headset and— the detector is ready. Now we can «listen» how the lamps blink, even if that blink is imperceptible to our eyes.

The solar panel, unlike our eyes, manages to fix even many short-lived falls in brightness that are elusive from sight, but in some cases have depressing effects on the nervous system. The solar panel voltage changes to the beat with the brightness fluctuations, and the headphones sound these changes in voltage.

You can find the flicker frequency by the height sound, by volume — the relative amplitude. A standard incandescent bulb may be taken as a standard because the amplitude of its flashes is very small and does not have a significant effect on the body.

For the video, we made a second version of the flicker indicator and plugged it into a portable recorder for recording audio. As you can see, using this simple device can not only detect high-frequency fluctuations in the brightness of light, but also receive light information. An LED or laser can be used as a transmitter.

In the video of our experiment, when turning on a LED table lamp, a sound a little higher than the note salt in the high octave appears, which corresponds to a frequency of 100 Hz — one hundred fluctuations per second. This means that the lamp also flickers with such frequency. The current frequency on the grid is 50 Hz,but during each sinusoidal cycle the lamp flashes twice — in the positive and negative half period.

How much the lamp manages to reduce its brightness in the breaks between flashes depends on the amplitude of the flicker and the harmful effects of the organism. Ripples are thought to be 2-3% deep at a frequency of 100 to 300 hertz are already negatively affecting brain function.

In our case, the power of «sound» from LED lamps, for example, it corresponds to an ordinary incandescent lamp at the same listening distance. This means that the amplitude of its oscillations is not large and not dangerous to health.

To determine the frequency of oscillation in the sound in the home can be used any musical instrument or program smartphone analyzing sound frequencies. Here’s what we got when analyzing audio using a mobile app:

Another LED lamp that was switched on during video recording — «be silent», means — does not flicker at all. Of course, such lamps are preferred. Unfortunately, during the shooting we did not find a single bad lamp for example, but in the near future we will definitely find and show the results of its «hearing» in a separate video.

To adjust the brightness of the television sets, computers, phones and flashlights commonly used high-frequency interruption of the supply voltage (pulse-width modulation, abbreviated as PWM), it can lead to oscillation, which may also be heard by using the solar panel and headphones.

Of course, this is not a professional tool, but it is much more reliable than «the pencil test» or the way to check the vibration with the camera of your smartphone. And the most important — much more interesting.

Check for flickering of a lamp by using «the pencil test»

Checking the flickering of a lamp using the camera of a smartphone