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Brad F (B_free)
New member
Username: B_free

Post Number: 1
Registered: 2-2007
Posted on Sunday, February 11, 2007 - 2:23 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

Hello All! :-)

I'm trying deperately to troubleshoot my Laser Communicator which is (obviously) not working.

Can anyone tell me what kind of voltage range I should expect to be getting from my solar panel when the music is turned on and the transmitter is functioning?

As my setup exists: my solar cell gives the reciever's mini-plug a voltage the fluctates between 93.8 millivolts and 97 millivolts when the music is turned on at full volume.

With the laser on but no music, the solar cell gives about 91 millivolts. (I have a digital multimeter, so its actual reading fluctuates between 90 and 92 millivolts.)

Bottom Line: Is this voltage about what I should expect to be getting at the mini plug (therefore my problem is in the stereo I'm plugging my reciever into)???
-or-
is this not the kind of voltage I should be getting (therefore my problem is either in the reciever itself, or the transmitter)???

Thank you so much in advance everyone for taking the time to look at this!!! (I've been trying to get this to work, off and on, for almost a year! :-) )
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1637
Registered: 12-2004
Posted on Sunday, February 11, 2007 - 3:08 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

You can test the receiver by holding the solar cell close to
a fluorescent light bulb. You should hear a strong 60 cycle
hum. Holding it up to a television, you should hear a higher
pitched whine.

The voltage will depend on the ambient light, the size of the cell,
the quality of the contacts, and other variables, and is not a
good troubleshooting metric. It should vary quite a bit between
having the cell in the dark and in the sun, and that will tell
you that your connections are OK, and to look elsewhere for the
problem.

If your amplifier has microphone input or phonograph input,
use one of those instead of line input. The input impedance of
the line-in input may be too low, placing too much load on the
solar cell (acting like a short circuit).
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Brad F (B_free)
New member
Username: B_free

Post Number: 2
Registered: 2-2007
Posted on Sunday, February 11, 2007 - 4:54 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I tried your suggestion, I plugged my receiver into the microphone port of my stereo, boosted the volume as loud as it could go, pressed "record" and shone a fluorescent light bulb on the solar panel. I couldn't hear any noise of any sort.

This would seem to suggest that my stereo/amplifier isn't working... but yesterday I tried to rule this out by hooking my music source (which is an iPod) directly to that same stereo's microphone input by using a cord with mini-plugs at both ends (and pressing record). The result was that I could hear the music out the stereo just fine. (Btw, the voltage off the mini-plug that went into the microphone jack was fluctuating between about 1mV and -1mV.)

But getting back to just now, I also tested the voltage on the receiver's mini-plug and it was about 300 mV with the light on, and as soon as I shut off the light it went down to around 40 mV or so. I just didn't hear anything when it was plugged into the microphone port.

By the way, if it helps... my solar panel is a Radio Shack 276-124 (the kind where the positive/negative terminal instructions on the box are completely wrong) but since I'm reading voltage I assume I've got it connected correctly.

Hmmm... here's something that might also make a difference. Before I found your forum, I tried reducing my signal to noise ratio by placing my solar panel at the back of a long kind of tube (Please see below :-) ). It's about a foot long, but it means that I couldn't get the fluorescent bulb any closer to the panel than that. Would that explain why I couldn't hear the buzz?

image

image

Also! Thank you so much for responding to my post!!! :-) I am amazed that not only do you still respond personally to newbies like me... but that you also do it so fast!!! Thank you very much, Sir!!!
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1638
Registered: 12-2004
Posted on Sunday, February 11, 2007 - 7:19 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

You should definitely try the test with the solar panel out of the box,
and closer to the fluorescent light.
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Brad F (B_free)
New member
Username: B_free

Post Number: 3
Registered: 2-2007
Posted on Monday, February 12, 2007 - 7:56 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

I took my solar panel out of that box, plugged it back into my stereo/amplifier, and then held my fluorescent blub desk lamp as close to the panel as I could (~1 inch or so) unfortunately I still couldn't hear any buzzing.

(There is a small amount of buzz that's present whenever I put the speakers up to their highest volume, but that buzz didn't change in any way whether the bulb was shining on the solar panel or not. It didn't even change when I unplugged the receiver entirely.)

I assume this means my stereo/amplifier is insufficent for the solar panel receiver. Can you recommend anything else that might work to make the signal clearly audible in a room?

Thank you very much again!!! :-)
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1640
Registered: 12-2004
Posted on Monday, February 12, 2007 - 8:19 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

"http://www.radioshack.com/product/index.jsp?productId=2062620&cp=2032062.2032398.2032405&parentPage=family"
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Brad F (B_free)
Junior Member
Username: B_free

Post Number: 4
Registered: 2-2007
Posted on Wednesday, February 14, 2007 - 1:26 am:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

That certainly did the trick! The buzz of the fluorescent light comes in loud and clear through that Radio Shack amplifier! :-)

Unfortunately, now I know my transmitter assembly isn't working either. :P

Right now my assembly is being powered by the 3 "button cell" batteries that came with my laser. In the past I've used 3 AA batteries for power, but everytime I do I seem to damage the laser. I'd turn it on and after a few seconds, the laser becomes considerably dimmer.

However, I haven't included the bicolor LED yet. (Is this something else that Radio Shack carries? I've searched their site but not found it.) If I can find that tomorrow I'll certainly plug it in!

Alternatively, would a 0.2 Ohm Resistor work instead of the bicolor LED? (Assuming it would be plugged in between the battery & the laser, not a short circuit.)
I'm trying to test how well I understand this material so please bare with me if I'm totally off my rocker... :-)
According to my multi-meter, 3 AA batteries produce about 2.7 Amps of current and about 4.8 Volts. When I check the button cell batteries, they deliver only about 4.3 Volts. Since I want a 0.5 Volt reduction from the AA batteries to the laser (to make sure I don't harm it), I'll use the equation R=V/I, plug in 0.5/2.7 and get 0.185 Ohms. Would this work too, or is my equation off since I didn't account for resistance across the laser?

Thank you very much for letting me ask all these questions!!! I really appreciate it!!!
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Simon Quellen Field (Sfield)
Senior Member
Username: Sfield

Post Number: 1642
Registered: 12-2004
Posted on Sunday, February 18, 2007 - 5:45 pm:   Edit PostDelete PostView Post/Check IPPrint Post   Move Post (Moderator/Admin Only)Ban Poster IP (Moderator/Admin only)

See "http://scitoys.com/board/messages/7/4012.html?1171838425".

The laser needs the current to be in a specific range.
Too little, and it's just an expensive LED.
Too much, and you damage it, and it becomes either an
expensive dim LED, or a Dark Emitting Diode (DED).

The voltage doesn't matter, as long as the current is within
the proper limits. The bicolor LED prevents the voltage at
the laser from getting out of range, and thus (due to Ohm's Law)
it keeps the current from getting out of range.

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