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Using IR receivers and high power IR LEDs


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#1 mikelwrnc

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Posted 23 October 2014 - 10:49 AM

I'm looking to create a near infrared spectroscopy system, which requires that I alternate turning on high power LEDs of different wavelengths and simultaneously measure the reflections of the resulting light. The low-wavelength LEDs (http://canada.newark...-red/dp/55T6493) have 2.4v forward voltage and 1A forward current; the high-wavelength LEDs (http://canada.newark.com/ledengin/lz1-30r400/led-infrared-5w-850nm/dp/48T1419) have 2v forward voltage and 1A forward current; the receivers (http://canada.newark.com/honeywell-s-c/sd5620-001/photodiode-schmitt-o-p/dp/06WX3601) expect a 4.5v minimum voltage and 4mA current.

 

I'm new to electronics and having trouble figuring out if any of the labjack models can drive the LEDs, letting me switch them on and off at will, while also reading from the receivers. (and, if so, how many low-LED/high-LED/receiver triplets I can use; note that I wouldn't need to turn on/off each LED independently, just the low-LEDs and high-LEDs independently from one another).



#2 LabJack Support

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Posted 23 October 2014 - 12:59 PM

The receiver is no problem, but the LEDs require too much current.  You need to provide a power supply that can drive them, then use a LabJack to control some sort of switch that you put in series with that power source.  I suggest a current source, so you can set it to provide the desired current (e.g. 1 amp) and then it will change the voltage as needed to provide that current.

 

For the switch, consider the Kyoto KF0604D which is a DC/DC SSR:

 

http://www.jameco.co...10001_175222_-1

 

This SSR will drop about a volt, so your power supply will have to provide 3-4 volts.



#3 mikelwrnc

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Posted 28 October 2014 - 09:48 AM

Since I had to go to an external power source anyway, I decided to bump up to the LEDEngin LZ4 series of LEDs (http://www.ledengin..../LZ4-00R308.pdf, http://www.ledengin.com/files/products/LZ4/LZ4-00R408.pdf), which have 9.6V forward voltage and 1A forward current. Do you think the MPDCD3 (http://www.mouser.com/ds/2/93/m_p-21177.pdf) would suffice as a SSR for these LEDs? Also, would you have any suggestions for current source? I'd like to plug into AC, and will have 2 LEDs (so 2A total current required).



#4 LabJack Support

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Posted 28 October 2014 - 10:24 AM

The SSR you linked is rated for 3A DC, so should work for you.

 

 

For a current source you can use a standard benchtop supply such as:

 

http://www.amazon.co...d/dp/B00FPU6G4E

 

You would turn the voltage knob to max, then use the current knob to set current as desired.

 

 

Another option rather than a power supply and SSR, is to use a programmable power supply such as the 382275 from Extech.  You can use the DAC outputs from the LabJack to control this power supply and thus no SSR is needed.

 

http://www.extech.co...d=39&prodid=546



#5 mikelwrnc

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Posted 28 October 2014 - 12:48 PM

Actually, I think it would be cheaper and work just as well to use an LED driver that has PWM support (this one seems to support the voltage/amperage required by the LEDs: http://www.ti.com/li...link/lm3434.pdf). I could then use a digital out from the labjack to send it high/low PWM signals to turn the LEDs on and off. Extra benefits are that it will automatically keep the current constant and can take pretty standard wall-plug power supplies. I'd have to have one driver per LED set to be able to turn the sets on/off independently, but these are cheap enough to make that moot.




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