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So right now I have a small solar panel (4" by 4") and a red laser. I'm trying to design a laser tag system that doesn't follow the way that traditional laser tag is done. I want to be able to shoot a modulated laser signal from a long distance and have my solar panel hooked up to a micro controller and read the output from my solar panel. (I know a solar panel isn't the best option for a sensor, and I will eventually use something more practical like a photo diode, but the basic principles remain the same). When I am reading the signals on my solar panel, there is so much sunlight that it masks the laser signal that I am sending. So its hard to program the micro controller to read the signal when I don't know what the signal even is.

I have thought about implementing a band pass filter, so that only frequencies of the color light I am using get through the circuit, and then putting another modulation on top of my laser to distinguish it from the sunlight signals that also made it through the filter. It sounds like it would work in theory, and I haven't done enough test to confirm it, but I have a feeling this might not work due to my next point.

If the solar panel becomes saturated in direct sunlight, then my signals my not even be producing a recordable output on my solar panel. If that is the case, what would I need to do? I would physically need to block the sunlight in this case right? Like put some barrier over the panel that maybe on lets in a narrow band of light that is specific to my laser? It would just be easier to do this whole thing if there was just a way to completely block all sunlight. Then I would definitely know the output on my solar panel was my laser. Is this at all possible? My gut tells me no because that would be too easy. I guess I'm just looking to see if I am on the right track with this thing and would love any suggestion you guys have to offer.

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  • \$\begingroup\$ Laser tag doesn't really use lasers, but rather focused infrared from an LED. Other than that, you need to modulate the transmitted signal with something that is easy to separate from sunlight. Remote controls using infrared modulate the LED signal at around 38kHz, then pass the received signal through a relatively narrow filter centered on 38kHz. That rejects most noise and ambient light. \$\endgroup\$
    – JRE
    Apr 1, 2017 at 9:53

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A large solar panel like yours will have lots of capacitance. This means modulation will not work. You need a small sensor, with low capacitance, to avoid lowpass filtering your modulated signal into oblivion.

The laser tag I played used normal red lasers, but it was in the dark.

Most important is modulation. I presume you cannot put a sunshade on the target, if it is carried by a moving player.

Then, I suggest an optical bandpass filter, matching the optical wavelength of your laser. A bit of transparent red plastic would be a crude way to start for a red laser... Using a more narrowband filter would remove more of the sunlight of course.

An optical sensor sensitive only to your laser wavelength could work, too.

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  • \$\begingroup\$ The problem is that the sunlight spectrum also contains IR waves. So, using a light bandpass filter will also pass them along with your laser light. So, if the irradience is stronger than of your laser, you will have a hard time detecting it. Of course, the sunlight decreases in intensity with larger wavelengths (far IR), the sensitivity of the sensors does so too. You just have to experiment and make some assumptions about maximum noise level (sun light). Then, lowpass your signal to have only modulation. \$\endgroup\$
    – Nazar
    Apr 1, 2017 at 13:24
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    \$\begingroup\$ Well, a bandpass should at least remove a large portion of the sunlight, which is basically a DC offset. As long as the sensor and electronics aren't saturated, a modulated signal should be detectable. \$\endgroup\$
    – bobflux
    Apr 1, 2017 at 14:31

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