Ir led low range

I need to control my a/c from Arduino but the ir range is too short. The ir led is from an old remote so I don't know its datasheet . How can I increase the TX power of the ir led?

How much current are you giving the LED now? Or, what is the value of the current limit resistor and the amplitude of the pulses from the Arduino? You may be able to lower the resistance to provide more current and increase the range.

I'm giving 5v from arduino to the led and however I'm not using nothing resistor. How many ohm must be the resistor?

If you drive a LED directly with a digital output you will likely damage the LED and/or the Arduino. To calculate a resistor value you need to know the LED current (If), the LED voltage drop (Vf) and the LED supply voltage. The safe current to be supplied by an Arduino output is about 20mA so we use that for If. A typical IR LED forward voltage drop is about 1.5V. The current limit resistor value is R = (Vsupply-Vf)/If or R = (5-1.5) / 0.02 = 175 ohms. A close standard resistor is 180 ohms. If you want to drive the LED with more current than 20mA you will need a transistor to source/sink the current. Once connected you can use a cell phone camera to see if the LED is actually turning on (cell phone and most digital cameras are sensitive to IR).

The led turn on, I already checked it using a camera. The problem is that it work only for a short distance(about 2-3 meters). Anyway I will to try with a 100ohm resistor

Probably not what you want but this is an option.
Extender

If you want to provide more than 40mA here is a transistor circuit that will provide about 50mA.

groundfungus:
If you want to provide more than 40mA here is a transistor circuit that will provide about 50mA.

How much distance can cover it about?

JohnLincoln:
Many Infra Red LEDs of the types found in remote controls can be used at an average current of 100mA.

Yep.

The problem is not enough amps. You need a transistor+resistor.

I’ve tried with a 100ohm transistor and it not work… I will try to replace the led

here is a description of a constant current Ir emitter circuit:

adjusting the resistor will increase range.

I have a p2n2222a, can I use it?

should be fine - as the max current rating is 600mA (Ic) and you should try to keep the current below 100mA(peak).

groundfungus:
If you want to provide more than 40mA here is a transistor circuit that will provide about 50mA.

More like 35ma if you have no voltage drop across your 5v supply
... with usb power 30ma give or take, but not 50ma

Either way, IR can handle more current than regular LED's there are 10mm leds which handle few hundred ma or was it mw, I'll have to check them out again

I've tried with another led, with a 100ohm resistor but the range is very short :/. I also have tried without resistor and after a few of pulse it burn out. My A/C remote control work up to 6-7 meters! Why?

I guess the good news is that it worked & the bad news is that a Led died in the process... :blush:
(Check the datasheet for your IR LED, so as you will know the max current to design for, which is important)

You can increase the current, hence the range, by implementing the circuit already posted by @Groundfungus.
Unfortunately, you wont get much more range driving the IR LEd directly from the Arduino via a resistor alone. You need a transistor type approach to increase the current going through the IR Led.

If you want even longer range just decrease the 68R resistor value. (to 47R or 22R).

This resistor acts as a current limiting resistor for the IR LED.

Typical IR Leds have a forward voltage of circa 1.5V. This will leave circa 3.5V across the resistor which results in 3.5/68= 0.51 Amps or circa 50mA. (see Ohms Law).

(note this is just an approximation)

By decreasing the resistor value you increase the current & thus the range of the IR.

Good IR LEDs are rated for up to 100mA - typical current. However, IR signals are modulated and if you are using IRremote which has 33% modulation duty cycle by default - you can calculate for 200 or even 300mA peak in the above calculation, which should average out to below the 100mA rating. (47R will get you about 70mA peak & 22R will get you about 150mA Peak, assuming circa 3.5V across the resistor, in ideal conditions). You could go with a smaller resistor value again, but make sure you have some spare just in case.

In summary, just decrease the value of the resistor from 68R until you are happy with the range and stay within the max rating for each component.

Yet another, circuit is provided in our earlier below, which is a constant current design.

Finally, some Leds are designed with different 'angles', which can be checked in the data sheet. Wider angles will give shorter ranges than narrow angle Leds.

I haven't tried yet with the transistor.. I will try it and post the result!
P.S. Many LED are died during the test :smiley:

With delay, I've tried the circuit with the transistor but the led light is very low...I've also tried with others led but the result is the same :frowning:

IR LEDs from remotes have quite a wide beam angle and work at quite a low power, so the range won't be very good. To increase range, you could use IR LEDs with a narrower beam angle and/or higher power output.

See http://uk.farnell.com/infrared-emitters for a selection of IR LEDs. The higher the value in the Radiant Intensity column, the more range you will get - but you also need to consider the value in the Viewing Angle column to see how accurately you need to point the IR emitter at the aircraft to get that range.

Bear in mind that the radiant intensity you need increases as the square of the range. IR control is typically used only for very short range models. It can also be swamped by sunlight, so it works best indoors.

It would be a good idea to post a diagam of your circuit.

+1 on the Led angle / power. TASL6100 is a good one and can take lots of current.