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I've been planning on putting together a laser tag system and one of the big concerns I have is that photoresistors/phototransistors have relatively small surface areas w/r/t a human body. On the other hand, solar panels have lots of surface area and the scrap ones are cheap enough to slap on a vest.

I've been doing some digging and I found this video where some students at a university manage to detect a modulated laser with a solar panel. They don't mention much in the way of parameters however. I don't know if it was a consumer grade laser pointer or if it was a commercial grade laser, for example. Neither do I know if the panel was extremely sensitive or if it was just any cheap panel they had around.

So I've come with questions. What are the basics of working with solar panels in terms of output characteristics? What equations do I need to know?

Second, does anyone have experience with either lasers or panels (preferably both) who might be able to point out any obvious pitfalls I've overlooked.

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    \$\begingroup\$ I can't say I've ever done anything similar, but one thing worth looking at is the capacitance of the solar cells. They may have a fairly slow response time compared to a photodiode (I'm not sure just something to check into or try testing with a modulated LED maybe). \$\endgroup\$ – PeterJ Aug 31 '13 at 4:05
  • \$\begingroup\$ Normally panels are chained together but that also increases the capacitance so it seems I'll have to wire each panel individually to avoid that. I just received my first batch of panels so I'm planning on experimenting over the weekend. \$\endgroup\$ – Huckle Aug 31 '13 at 6:35
  • \$\begingroup\$ If the targets are engaging in vigorous activity, like running away or shooting back, those large area rigid solar cells will be quite vulnerable to damage. Either try to source flexible plastic solar panels, or consider optics to scatter the laser beam to a few inches at typical range. e.g. piezo mounted mirror to deflect the beam, providing divergence and modulation at the same time. Then small sensors may be feasible. \$\endgroup\$ – Brian Drummond Aug 31 '13 at 9:06
  • \$\begingroup\$ very similar question here: electronics.stackexchange.com/questions/66966/… I suggest photo-daringtons with ping pong ball diffusers. \$\endgroup\$ – Bobbi Bennett Aug 31 '13 at 13:10
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    \$\begingroup\$ Maybe if you modulate each laser, at a few Khz? That will let you reject ambient light a lot better (a real problem for any large area detecting scheme), with the bonus of being able to code each laser with its own id. \$\endgroup\$ – Bobbi Bennett Sep 3 '13 at 1:00
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In general, you can detect laser with solar panels. There is intensive research on possibilities of employing lasers in wireless power transmission (Laser Power Beaming). Laser Power Beaming have already been used in order to provide energy for remotely controlled machines (example).

It is my belief that we are 20-30 years from the point when Laser Power Beaming from orbital based photovoltaic power collectors (satellites) will be possible (remember SimCity?).

That said, it seems like you are not that into wireless power transmission. I guess you want to use laser as means of transmitting some information to an electrical circuits which get attached to humans clothes, right?

Well, I've seen (and used) few military combat simulation systems which employ lasers in order to allow soldiers to shoot at each other (without killing each other). Even those systems which are vehicle mounted did not use photovoltaic cells in order to detect laser radiation.

We could provide you with a bunch of information about photovoltaics and lasers, but I believe that your initial direction is incorrect. You can use several photodiodes scattered over the body in order to increase the coverage of your system - it will be cheaper, simpler and much more durable approach.

If sensitivity is your concern, you might want to check out for photomultiplier. These devices have very high sensitivity, but are more complex and more expensive than photodiodes. They are also much more prone to mechanical damage.

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  • \$\begingroup\$ I understand this is not the standard method for going about doing this. But I wonder, how many photodiodes do you mean when you say "several"? 10? 100? I'd argue the surface area of an array of 2cm by 8cm panels easily surpasses 50-100 photodiodes. I think the diodes would be unfeasible. I know it is generally possible to do, I was asking if anyone knew specifics. Is there a general formula with inputs for wavelength and power and output for voltage? What are the part-specific coefficients and how would I go about measuring my panel's coefficents? \$\endgroup\$ – Huckle Sep 3 '13 at 0:15
  • \$\begingroup\$ @Huckle, I meant to say that you might want to use several photodiodes scattered over the body in order to detect laser radiation from different directions. I agree that it is not feasible to manually build arrays of tens of photodiodes in order to detect the radiation. I can try to give you few practical advices as to how to choose an appropriate photodiode (or other detector), but you need to provide more information regarding the laser in use and the expected irradiance on the detector. \$\endgroup\$ – Vasiliy Sep 3 '13 at 6:46
  • \$\begingroup\$ My goal is to use off-the-shelf lasers such as those found in either red or green novelty laser pointers. If those turn out to be non-optimal in terms of power or frequency I would consider using commercial parts. (Or if commercial parts are just cheaper) \$\endgroup\$ – Huckle Sep 4 '13 at 4:03
  • \$\begingroup\$ The huge collection area of a single solar cell ----single cell--- is your friend. Area is 10,000X that of a photodiode/phototransistor. For speedy response, run the cell into Virtual_Ground (Pin-) of OpAmp, with some feedback resistor shunted with back-back silicon diodes. Problem with solar cells is the DC energy from SUN and 120Hz energy from incandescents and ....... \$\endgroup\$ – analogsystemsrf Feb 1 '17 at 18:35

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