IR LED air conditioner control power

Other Hardware LEDs and Multiplexing
1

I have this simple IR led transmitter project that I managed to program my a/c codes into. Its basically an UNO with an IR led Tx along with transistor and resistors which I currently power from a battery bank connected to the usb port of the arduino whenever i need it.

The issue is that I have to have the IR led about 12" from the a/c at least in order for it to work. What would need to be done for it to work from a normal distance of about 5 feet, which is what the remote control works at?

PS im not posting the diagram cause i dont have one made and I dont think its necessary for the question but will gladly make one if it is indeed required.

2

Hmmm. Maybe you do need to provide a schematic. :face_with_raised_eyebrow:

3

IR LEDs need a lot of current, compared to a red LED. How are you powering the IR LED and how are you controlling it?
Paul

I guess you have it covered, but you need to measure the ma going to the LED. Bet is it way too low.

4

ok here is the schematic. I believe the pwerbank is a 5V, not sure about the current but im guessing its not too much since its for charging iphones/ipads. Id guess about 1A max.

But I just remembered the arduino pins are limlted to something like 200mA?

Screen Shot 2021-08-01 at 6.51.08 PM
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5

Then what is the current, in ma, going through the LED?
Paul

6

hmmm...not sure i know. If i set it to high, yikes, apparently the max current draw from a digital pin is 40mA.

How much would I need for it to travel 5 feet?

7

Test it!

8

Why is that relevant? You are powering the LED from the 3V3 line according to your "schematic"
https://forum.arduino.cc/t/how-to-make-a-schematic-you-can-post/675103/12

However the LED has no resistor to limit the current; and I cant read the value of the base resistr to the transistor.

9

So that is going to significantly limit the current available!

10

As others have noted, the transistor circuit isn't right.

Get that straightened out.
It wouldn't hurt to add IREDs, more irradiance (illuminance).

PE - I don't know about IREDs "needing" more current than others, but they are usually spec'd for more ("30mA") than visible light LEDs.

11

oh that's right, sorry, i thought i was powering it from a digital pin. And the resistor was supposed to be a 470ohm, but i didnt have one so I used 2x220 Ohms.

12

Yeah sorry about the diagram as well. Luckily that is NOT how I had it wired, i just messed up the schematic.

Screen Shot 2021-08-02 at 4.05.45 PM
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So its 50mA to the IR led.

13

Still not right - no resistor there for the LED/Collector.

14

ok now, please explain why that would be necessary? I would think that a resistor would reduce the current flow in that circuit. Thanks in advance

15

It controls the current.
Without, it's "limited" by what the power supply can deliver (not unlike a short circuit).
https://en.wikipedia.org/wiki/Common_emitter

16

ill have to revisit my notes :slight_smile:

Ok so any particular value I should use on Vcc-Collector?

17

220Ω.

18

Ok i added the resistor. Now what do I need to make the signal travel longer? Because I still have to place the IR about 12" from the receiver when the remote works from 8' away.

19

I'm going to go with (as suggested previously) -- add more LEDs.

20

You can also get IR LEDS with a very narrow "viewing angle" which will tend to concentrate the beam. It needs more accuracy in positioning it but should give a longer range. Example: https://www.mouser.ch/ProductDetail/ON-Semiconductor-Fairchild/QED123?qs=KIIz7VjqD7I4A%252BR7oPm1DQ%3D%3D

This has a quite narrow 8 degree viewing angle and has a 100mA current rating.