I'm BRAND NEW on this help me understand something

cdesigns

I bought the Basic STAMP kit from Radio Shack, saw it for the first time last week. I love to make inventions regarding R/C stuff, Burning Lasers and diodes, CCD cameras, GPS, wireless stuff, etc etc. I have never used a microcontroller. I bought this microcontroller because it says that it can measure light with the photoresistor, I'm into CREE LED's also. Just wondering if I can measure LASER·light power in·mw also. Or how does this basic kit measures light?

Here is the microcontroller (sorry for the mess I was cleaning a little)


·

RDL2004

Hint, hint [noparse]:)[/noparse]



▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
- Rick

Mike Green

The parts kit does include a photoresistor and the manual shows how to measure the resistance of the photoresistor. You'd have to calibrate the whole setup for light intensity vs. resistance and I don't know how you'd work out the conversion between power and light intensity. I'm sure there are some datasheets that would help some and show the relationship between light wavelength and intensity and photoresistor response.

cdesigns

I tried using the 0.1uf capacitor for brighter light conditions and played with the Plot Lite software changing values etc, but if I set my CREE flashlight to low mod, the measurements hit ZERO to quickly. I'm still searching if someone have done this before.

I need to measure:

Lummens for flashlight CREE L.E.D output
Milliwatts of power for my laser diodes

PS: is there anyway to change how the software reads the data from the photo resistor?
right now is set to show lower numbers when is brighter, and larger numbers when is dark. I need this to be the oppositive. Maybe is a dumb question but I don't know if is possible.

Post Edited (cdesigns) : 3/9/2008 12:14:13 PM GMT

LoopyByteloose

I suppose you should start with that very good book in the picture - What's a Microcontroller?
Regarding measuring lasers, sure it certainly can be done. The only things you have to consider is what are you using for a sensor and does the laser provide too much power for the sensor to survive. Usually, one would provide filters and appertures that would reduce the amount of power received by the sensor.

For a light sensor, the usual fast response one is a 'photo transistor', even an LED will work as a photo-transistor. And some photo transistors are designed specifically for certain wave lengths and for high accuracy. I have one that is an accurate photographic meter sensor. You·seem to·be using a photo resistor which is a CadiumSulfide device. The response is slower and the accuracy is not much to shout about. They work fine for light seeking robots and teach you about measuring with RC circuits, but are not really a scientific measuring device.

Of course, the real dilema with measurement is you have to have a good reference to calibrate your measuring device. It becomes a paradox. Why would you build a measuring device if you already have one? One good reason to do all this is it really is a winner in a Science Fair. You not only demonstrate the theory, but you have to work with the practical problems of getting an accurate device.

BTW, the photo transitor or photo diode is more complex to work with.· It generally needs to be amplified before it is measured.· There is a whole Parallax kit on instrumentation that explains these things - but one step at a time. Learn the basics thoroughly and it will all make sense.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
PLEASE CONSIDER the following:

Do you want a quickly operational black box solution or the knowledge included therein?······

···················· Tropically,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

Post Edited (Kramer) : 3/9/2008 1:40:51 PM GMT

Tracy Allen

To estimate the power output of the laser, you would need a good large-area photodiode, such as ones from Advanced Photonic Devices. There is one of those in the Parallax "applied sensors" kit along with some text about quantitative measurement of light levels.

To measure, (assuming it is a low power diode, < 5mW), you can direct it at the photodiode and measure the current produced in miliamps. Suppose you measure 0.95 milliamp (0.00095 amp). In the photodiode data sheet, you will find a parameter of "amps per watt" as a function of wavelength. If you know the wavelength of your laser, you look up the corresponding amps per watt on the graph. Suppose it is 0.42 amps per watt (that is typical of a photodiode at 650 nm red). Then divide: 0.00095 / 0.42 = 0.0023, or 2.3 milliwatts. The entire laser beam has to hit the photodiode and the beam can't be too intense or it will saturate or damage the photodiode--Don't use that method with an industrial laser. You can purchase calibrated photodiodes, but they are expensive, and you only need that if you want to get to another decimal place.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

cdesigns

Tracy Allen said...
To estimate the power output of the laser, you would need a good large-area photodiode, such as ones from Advanced Photonic Devices. There is one of those in the Parallax "applied sensors" kit along with some text about quantitative measurement of light levels.

To measure, (assuming it is a low power diode, < 5mW), you can direct it at the photodiode and measure the current produced in miliamps. Suppose you measure 0.95 milliamp (0.00095 amp). In the photodiode data sheet, you will find a parameter of "amps per watt" as a function of wavelength. If you know the wavelength of your laser, you look up the corresponding amps per watt on the graph. Suppose it is 0.42 amps per watt (that is typical of a photodiode at 650 nm red). Then divide: 0.00095 / 0.42 = 0.0023, or 2.3 milliwatts. The entire laser beam has to hit the photodiode and the beam can't be too intense or it will saturate or damage the photodiode--Don't use that method with an industrial laser. You can purchase calibrated photodiodes, but they are expensive, and you only need that if you want to get to another decimal place.

Well I tried adding one more capacitor and a variable resistor on one of the legs of the photoresistor, it helped a little but I still can get good readings, this was tested only with the CREE flashlights, on the lasers I might have to find more information, because I'm using green laser rated 30mw and 50mw, and red lasers rated over 200mw, I need a tool that can show me the power when I'm tweaking them. Plus I want the stamp kit to control the power of the laser in conjuction with my plotter.

·

Tracy Allen

I didn't know what a CREE flashlight was until you brought it up. I see they are available at prices ranging from $10 to $800. What's with that? I've been thinking about getting a little super-LED flashlight for backpacking, one of those powered by a CR123 primary lithium cell, but what is the advantage of CREE?

There is a lot of information on nice light measurement available at www.udt.com/. See the section of their web site called "Technology Corner".

One way to measure total output in lumens or watts is with an integrating sphere. That is basically a sphere that is mirrored or highly reflective specular on the inside, so that all the light is collected and all the modes and coherence and interference is lost by the time it reaches the detector. For a spread-out beam, a photodiode can measure at different angles, and you end up with a map of intensity versus angle, in watts/m^2 or lux, and then you have to integrate numerically to find the total source output in lumens or watts. The problem is more involved when many wavelengths are involved, because then you have to weigh in the sensitivity curve of the detector and the spectrum of the source.

CdS photoresistors have a peak response in the visible and can be quite sensitive. But they are not so linear and they do not have the wide range and linearity of photodiodes.

It is not hard to connect a photodiode in photoconductive mode to the Stamp using the RCTIME command.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tracy Allen
www.emesystems.com

cdesigns

CREE Flashlight are the best out there for the $, check my youtube video on how my CREE 5-mode flashlight (on the video you can see hwo different is the power on 3v CR123 and 3.6v CR123A batteries) I use rechargables 3.6v and this little flash light is BRIGHT. You can buy cheap lasers, cheap CREE flashlights and cheap almost everything·on this page,www.dealextreme.com they're based on hongkong but it's FREE SHIPPING on everything they sell, plus it arrives in 10days or less. I have order more than 20 times from them.

This is a $19 Flashlight, $4 for (2) Rechargables 3.6v CR123A batteries, $5 for the CR123A Charger = $28 Shipped

CREE FLASHLIGHT VIDEO 1 (Testing the 5 Modes Med-Low-High-Strobe-SOS)

http://www.youtube.com/watch?v=eaLfDuZvUeg

CREE FLASHLIGHT VIDEO 2 (testing 3v and 3.7v volts)

http://www.youtube.com/watch?v=JPdYAfnlV88

I'm uploading one more video on how it works outside so you can see the light output. DON'T buy normal LED Flashlights, Go buy a one cree flashlight on deal extreme, CREE Q5 and CREE P4 are good CREE LEDS

Tracy Allen said...
I didn't know what a CREE flashlight was until you brought it up. I see they are available at prices ranging from $10 to $800. What's with that? I've been thinking about getting a little super-LED flashlight for backpacking, one of those powered by a CR123 primary lithium cell, but what is the advantage of CREE?

There is a lot of information on nice light measurement available at www.udt.com/. See the section of their web site called "Technology Corner".

One way to measure total output in lumens or watts is with an integrating sphere. That is basically a sphere that is mirrored or highly reflective specular on the inside, so that all the light is collected and all the modes and coherence and interference is lost by the time it reaches the detector. For a spread-out beam, a photodiode can measure at different angles, and you end up with a map of intensity versus angle, in watts/m^2 or lux, and then you have to integrate numerically to find the total source output in lumens or watts. The problem is more involved when many wavelengths are involved, because then you have to weigh in the sensitivity curve of the detector and the spectrum of the source.

CdS photoresistors have a peak response in the visible and can be quite sensitive. But they are not so linear and they do not have the wide range and linearity of photodiodes.

It is not hard to connect a photodiode in photoconductive mode to the Stamp using the RCTIME command.