I did build an Arduino IR remote with one "5mm" 940nm IR LED powered through a limiting resistor to protect the LED using the IRremote library. This works okay but I'd like to get long range (about 20 meters) , i have found some cheap "1w infrared 940nm" under $2.
With regular little LEDs we use a current limiting resistor but for this LED you'd need a 5 Watt resistor as well as a transistor or MOSFET driver. (That method is almost never used with high-power LEDs.... The resistor takes more power than the LED.)
rbird:
I did build an Arduino IR remote with one "5mm" 940nm IR LED powered through a limiting resistor to protect the LED using the IRremote library. This works okay but I'd like to get long range (about 20 meters)
So what are you using now, how are you driving it, and what range are you getting.
You will have less range with a 125 degree power LED driven with the same current as a narrow beam 5mm LED.
A narrow beam 5mm LED pulse-driven with 200mA should do >25meters.
But you might need wide beam coverage (didn't say).
Leo..
You need at least a power supply for the intended current, and a transistor (MOSFET) to switch that current through the LED. The current limiting resistor must withstand the remaining power I*(Vsupply-Vled).
Wawa:
So what are you using now, how are you driving it, and what range are you getting.
You will have less range with a 125 degree power LED driven with the same current as a narrow beam 5mm LED.
A narrow beam 5mm LED pulse-driven with 200mA should do >25meters.
But you might need wide beam coverage (didn't say).
Leo..
I want 20-40m aiming in the general direction of receiver. It is even possible that there is more than one receiver, so pointing too accurately can be counterproductive.
Receivers at the same distance will get the same signal level. If you spread the beam too wide, the level may be too low for activating any receiver. Just then it's better to have a narrow beam (spot), to drop all the energy onto one receiver.
DrDiettrich:
You need at least a power supply for the intended current, and a transistor (MOSFET) to switch that current through the LED. The current limiting resistor must withstand the remaining power I*(Vsupply-Vled).
As far as I know with my limited knowledge the use of current limiting resistors is not feasible at these power levels. Also i would like to do it powered by a battery where the voltage drop can be a problem.
What I wonder is if I could use the use of batteries in my favor, I know that AA batteries do not give more than 500mA in ideal conditions. Could i directly feed the LED with 2xAA and switch it to a mosfet?
My calculator might be wrong, but it shows that you need 482 times the current for a 125degree LED than for a 10degree LED to get the same light level on the receiver.
Calculated for the same 40meters, a 10degree LED produces a spot of ~7meters diameter.
Several LEDs in series is an another way to increase distance.
Leo..
rbird:
Why do people insist on answering questions that are not even asked?
Maybe the questions asked are stupid.
Why would you use a flood light to light up a small item at 40meters distance.
Using the internal resistance of an AA battery is also weird. Some can source 10Amp.
Post#2 in this thread shows a standard mosfet driver circuit with current limiting.
Use a logic level mosfet, change R2 to 1.2ohm (for ~500mA), change R1 to ~330ohm, and use a >=3volt LED supply with a 1000uF buffer cap on the LED anode.
Leo..