Hello Everyone,
Please take the time to go through this rather long post. We really need your help.
My friends and I have decided to do a mini-project LED sun simulator as part of our undergraduate studies. Even if you don't know what that is, I think you can help with some parts. The requirements that we have imposed are:
· Well try to use circuits instead of ICs as much as possible.
· Were trying to keep the cost of the circuitry and LEDs around(preferably much less than) 500$ (or 25000 INR).
· Only the visible light spectrum is being simulated. High-Brightness (High Power?) LEDs with Six to eight wavelengths are used for this purpose. We are thinking of using Luxeon Star LEDs that come in typical wavelengths 447.5 nm, 470 nm, 505 nm, 530 nm, 590 nm, 617 nm, 627 nm and 655 nm.
· Class C specifications by ASTM E927-05 standard (Please see article on Solar Simulator in Wikipedia for details) are expected. AM1.5G spectrum is preferred.
· LEDs will be arranged in a flat panel with colours forming the vertices of a hexagon (for uniform distribution of light, 6 colours). We want to be able to switch on and off LEDs of specific wavelength (Eg: switch on LEDs with wavelength 470 nm) using a laptop and a microcontroller. We intend to send 8-bit data from the computer to the Microcontroller, reserving one bit for a specific LED set of a specific wavelength. The microcontroller would output a PWM waveform that is given to a DC to DC (buck) converter which would output a suitable current to forward bias the LEDs. The current should be constant.
· We intend to use a Rectifier and regulator (or perhaps implement an SMPS) to act as supply to microcontroller and the buck converters.
The block diagram of the system is shown as attachment. I think we'll be able to handle the circuits, but we have some points that we are doubtful of.
Please clear the following doubts we have before we proceed with this project.
· Is the Project possible with the set requirements? Can we really use a microcontroller to receive 8-bit data from a laptop, give a 6 or 8 channel PWM output accordingly? Would you please suggest a suitable microcontroller? Or should a Digital signal processor be used?
· Suppose we use about 8 High brightness LEDs of the same color, the distance form similar collared LEDs being 12 mm along the edges of a hexagon with edge length 4 mm. Based on a rough guess, what would be the Irradiance at, say, 300 mm below the LEDs?
· What is the minimum intensity of light required to perform solar cell testing?
· Can we try to get Class B specification on spectral match just by controlling the current through the LEDs, thereby decreasing the radiant intensity? Will this affect the wavelength of the LED output? If so, how significantly?
· Is there a need to output all wavelength lights for an LED Sun Simulator? (Eg: Will the user want random wavelengths like 600nm?). That is, are continuous wavelengths needed?
· How can we check if our simulator meets the standards? What are the testing apparatus required? Would this be affordable? Is there a low cost method to test the accuracy within class C specifications?
· Will we need a feedback from the current supplied at LEDs to check if it is constant? If so, how would we rectify the problem?
Please help us with these doubts. Even if you point us to the correct sources, wed be grateful.
Please take the time to go through this rather long post. We really need your help.
My friends and I have decided to do a mini-project LED sun simulator as part of our undergraduate studies. Even if you don't know what that is, I think you can help with some parts. The requirements that we have imposed are:
· Well try to use circuits instead of ICs as much as possible.
· Were trying to keep the cost of the circuitry and LEDs around(preferably much less than) 500$ (or 25000 INR).
· Only the visible light spectrum is being simulated. High-Brightness (High Power?) LEDs with Six to eight wavelengths are used for this purpose. We are thinking of using Luxeon Star LEDs that come in typical wavelengths 447.5 nm, 470 nm, 505 nm, 530 nm, 590 nm, 617 nm, 627 nm and 655 nm.
· Class C specifications by ASTM E927-05 standard (Please see article on Solar Simulator in Wikipedia for details) are expected. AM1.5G spectrum is preferred.
· LEDs will be arranged in a flat panel with colours forming the vertices of a hexagon (for uniform distribution of light, 6 colours). We want to be able to switch on and off LEDs of specific wavelength (Eg: switch on LEDs with wavelength 470 nm) using a laptop and a microcontroller. We intend to send 8-bit data from the computer to the Microcontroller, reserving one bit for a specific LED set of a specific wavelength. The microcontroller would output a PWM waveform that is given to a DC to DC (buck) converter which would output a suitable current to forward bias the LEDs. The current should be constant.
· We intend to use a Rectifier and regulator (or perhaps implement an SMPS) to act as supply to microcontroller and the buck converters.
The block diagram of the system is shown as attachment. I think we'll be able to handle the circuits, but we have some points that we are doubtful of.
Please clear the following doubts we have before we proceed with this project.
· Is the Project possible with the set requirements? Can we really use a microcontroller to receive 8-bit data from a laptop, give a 6 or 8 channel PWM output accordingly? Would you please suggest a suitable microcontroller? Or should a Digital signal processor be used?
- Would this count as a moderately complex electronic system? That's a requirement in the mini-project. If not, how could we make it satisfy the requirement?
· Suppose we use about 8 High brightness LEDs of the same color, the distance form similar collared LEDs being 12 mm along the edges of a hexagon with edge length 4 mm. Based on a rough guess, what would be the Irradiance at, say, 300 mm below the LEDs?
· What is the minimum intensity of light required to perform solar cell testing?
· Can we try to get Class B specification on spectral match just by controlling the current through the LEDs, thereby decreasing the radiant intensity? Will this affect the wavelength of the LED output? If so, how significantly?
· Is there a need to output all wavelength lights for an LED Sun Simulator? (Eg: Will the user want random wavelengths like 600nm?). That is, are continuous wavelengths needed?
· How can we check if our simulator meets the standards? What are the testing apparatus required? Would this be affordable? Is there a low cost method to test the accuracy within class C specifications?
· Will we need a feedback from the current supplied at LEDs to check if it is constant? If so, how would we rectify the problem?
Please help us with these doubts. Even if you point us to the correct sources, wed be grateful.
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