IR Remote Control Issues

[Kamikaze47]

Hi All,

I'm currently making a PIC controlled Infrared Remote Control so that I can control all the various components of my home entertainment setup from a PIC. So far i've been concentrating on my TV.

I have attached an image of the circuit i've made.

The point marked PIC(PWM) is connected to the PICs hardware PWM output, and generates a constant PWM or 48khz at 50% duty cycle.

The point marked PIC(I/O) is connected to one of the PICs digital I/O pins.

I use the PIC to turn on and off that I/O pin to output the correct sequence to turn on my TV.

And it works. However, the range is quite poor. It only works up to 2m away from the TV and only when the IR LED is pointed directly at the TV, whereas my regular TV remote works from anywhere and even if its not pointed anywhere near the TV.

The IR LED's specs are the following: 1.2V typical (2v max), 20mA typical (50mA max), 14-28 mW/cm2

Anyone have any ideas on what may be wrong?

[mackrackit]

What is the angle of the IR? The wider the angle the less range.

[Kamikaze47]

specs say viewing angle 20 degrees

[Jumper]

Is it the correct wavelength? 950 nm is popular but so is also eight-hundred something and so on..... less correct -> less sensitive receiver

Is it the correct frequency? 40? 48? 56? kHz there are plenty to choose from.... pick the wrong one and you loose performance

Do you provide enough current thru the LED? Even if the LED is specified 50 mA MAX that usually means that it can handle 50 mA constantly. Since you have a 50 % dutycycle and then send bursts out it can take much more. There is a chart in the datasheet that shows max current for different dutycycles. Now you have 30-40? More is better...... many receiver datasheets mention distance when the LED currenct is 100 mA.

I am happily running my IR led's at 700 mA and that is more than enough to change channel for the whole apartment area.

Of all these questions the easiest to solve is frequency (if you have a scope). The others are more or less up to trial and error...

Break open the TV and see if the receiver chip has any markings, then you might get both FQ and wavelength.

/me

[Kamikaze47]

These are the specs on my IR LED:

Parameter                   min    typ    max   unit     test conditions
---------------------------------------------------------------------------------
radiant power               14     -      28    mW/cd2   If=20mA
peak emission wavelength    -      -      940   nm       If=20mA
spectral line half width    -      -      50    nm       If=20mA
forward voltage             -      1.2    2.0   V        If=20mA
reverse current             -      -      100   uA       Vr=5V
rise time                   -      -      200   nS       PW=10uS DC=10% Ifp=20mA
fall time                   -      -      500   nS       PW=10uS DC=10% Ifp=20mA
power dissipation           -      -      150   mW       Vr=5V
continous forward current   -      -      50    mA       -
peak forward current        -      -      1     A        PW=10uS DC=10% Ifp=20mA
reverse voltage             -      -      5     V        -
viewing angle               -      20     -     deg      -
operating temp range        -45    +25    +100  degC     -
storage remp range          -45    +25    +100  degC     -
lead soldering temp         -      -      +250  degC     5 Sec 1.6mm from base

PW=Pulse Width
DC=Duty Cycle

The frequency of 48khz i found by trial and error. It def works best at 48khz.

How could i get 700mA with this LED? Pref with 5v only?

[dhouston]

I've never heard of a 48kHz carrier. 32-40kHz is common and there are some that use ~56kHz What is the make/model of the TV?

[Kamikaze47]

Ok, I just tried it with a 10 ohm resistor, so 340mA through the LED. It only seems to have made a very small difference to the range, and I still have to point the LED *directly* at the TV for it to work - Even a few degrees make a difference.

I will try playing with the frequency again.

Also, do you think 50% duty cycle is the best bet? I wasn't sure what to use, and 50% seemed logical, but now i'm considering a lower duty cycle as that means the LED should theoretically be able to handler a higher peak current.

*edit* My TV is a Samsung LA40R71BDX

*edit2* Fixed mistake in schematic (thanks keithdoxey)

[Jumper]

http://www.sbprojects.com/knowledge/ir/nec.htm

Someone said Samsung uses NEC code 38 kHz with a dutycycle around 0.25 to 0.33

HOW IS YOUR TIMING?

Increasing IR current that much would have made a difference if that was the true problem.

Do you have a scope so you can meassure the output of the TV remote control LED? (and if you have a nice digital one you might even post the pic)


/me

[ardhuru]

Ok, I just tried it with a 10 ohm resistor, so 340mA through the LED.

Just realised; if my math is right, you are *not* getting 340 mA thru' the LED with a 4.7K bias resistor; I would reduce that to 1 K; at the most 2.2 K.

Regards,

Anand

[keithdoxey]

Hi All,

I'm currently making a PIC controlled Infrared Remote Control so that I can control all the various components of my home entertainment setup from a PIC. So far i've been concentrating on my TV.

I have attached an image of the circuit i've made.

The point marked PIC(PWM) is connected to the PICs hardware PWM output, and generates a constant PWM or 48khz at 50% duty cycle.

The point marked PIC(I/O) is connected to one of the PICs digital I/O pins.

I use the PIC to turn on and off that I/O pin to output the correct sequence to turn on my TV.

And it works. However, the range is quite poor. It only works up to 2m away from the TV and only when the IR LED is pointed directly at the TV, whereas my regular TV remote works from anywhere and even if its not pointed anywhere near the TV.

The IR LED's specs are the following: 1.2V typical (2v max), 20mA typical (50mA max), 14-28 mW/cm2

Anyone have any ideas on what may be wrong?

Couple of things.....

1. The schematic for your LED driver has the IR LED the wrog way round !!

Assuming your switching transistors have a Vsat of 0.2V each and the IR LED has its lowest possible Vfwd of 1.2V then the resistor will be dropping 3.4v giving a current of 22.6mA.

2. Even if your TV is using a carrier frequency of 48KHz, its almost certainly wrong for most of your other kit. The three main families of IR codes are

Philips (RC5, RC6, RCMM) @ 36kHz
NEC and Vairiants @ about 38kHz
Sony @ 40kHz

Generally 38kHz is a good "catch all" frequency as 36 and 40k systems will still have pretty good reception.

You may find that you need to set your PWM to different values for different devices.