IR Remote Control Issues

[Kamikaze47]

Samsung uses 38kHz and sends a 32-bit code similar to the NEC protocol but with a shorter lead-in pulse and with the bits interpreted differently. Samsung uses a 4.5mS start pulse followed by a 4.5mS space.

Sounds exactly like what i've observed. Do you know of a page on the net somewhere that has more detailed info on the protocol they used? I havn't been able to find any info on it.

[Jumper]

When you PIC-scoped the remote what receiver did you use? What is the range and sensitivity using the standard tv remote control and this receiver?

Then we can get an idea of the FQ used. If you have good distance with the remote then it must be your LED that has a major output power problem. It might be burnt due to over current along the evolution chain.

Have you tried to move one thansistor to the base of the other, so you do all the mixing on the base.

Maybe just loose both transistors and sink current with the PIC and make a software mixer by turning on and off HPWM (and connect the led there with a resistor)

what partnumber is the led?
what part number is the receiver you have used?

/me

[dhouston]

Sounds exactly like what i've observed. Do you know of a page on the net somewhere that has more detailed info on the protocol they used? I havn't been able to find any info on it.

I don't recall seeing any detailed description. There is a simple description at http://www.techdesign.be/projects/011/011_waves.htm and there are CCF codes on RemoteCentral.com and at http://ir.premisesystems.com/. There are a few detailed descriptions of the NEC protocol. It was the first and was copied with minor changes by many others. Here's a datasheet for an early NEC encoder chip - http://davehouston.net/Nec6121.pdf

EDIT: BTW, I find it easier to record the codes as .wav files using a soundcard. This way you can use a wave editor to view them. See http://davehouston.net/learn.htm

OTOH, if you sample with a PIC using a phototransistor, you can get the carrier frequency and eliminate any guesswork.

[ardhuru]

Hi,

This technique should help you get a substantial improvement; instead of gating the LED using HPWM and a data pin, use the data pattern to control the HPWM pin itself (keep the HPWM running all the time, and just turn the HPWM pin to an input wherever you dont want a transmission); Darrel had suggested this during an earlier post pertaining to X10 transmission and it worked like a charm.

If nothing else, it would at least eliminate the drop across one transistor, and you would save a pin as well. You would also find the waveform far more consistent with the original remote.

Regards,

Anand

[Kamikaze47]

Ok, here's what i've done since the description in my original post:

- Changed the LED's resistor to 10 ohm
- Removed one transistor, turning on and off PWM to control the LED
- Changed the frequency to 38kHz
- Changed the duty cycle to 25%
- Improved the timing using TMR0 for timing instead of PAUSEUS

The end result is an improvement, but not spectacular. The range is improved, however I still need to point the LED pretty much directly at the TV for it to work - Whereas i can point my normal TV remote anywhere in the room and it will work (even pointing directly away from the TV).

Perhaps I need some kind of diffusing material in front of the LED? I'm not sure what to use tho. Or maybe I need to get an LED with a better viweing angle, but i'm not sure that this is the case, unless my tv's remote has a 360 degree viewing angle - lol. I assume that my tvs remote is simply powerful enough to bounce off the walls and eventually find its way to the tv no matter what direction i point it.

[keithdoxey]

Looking at the schematic again, I dont think you are getting enough drive to the transistors.

Either change the transistors to PNP types and invert your gating signal or put the transistors where the LED is and the LED where the transistors are so that the transistors are sinking current rather than sourcing it.

You may also need to reduce the value of the base resistors to get more drive.

[ardhuru]

Perhaps I need some kind of diffusing material in front of the LED? I'm not sure what to use tho. Or maybe I need to get an LED with a better viweing angle, but i'm not sure that this is the case, unless my tv's remote has a 360 degree viewing angle - lol. I assume that my tvs remote is simply powerful enough to bounce off the walls and eventually find its way to the tv no matter what direction i point it.

I dont think any external diffusing material would help. A lot of remotes have the LED body itself sticking out of the remote. You're right about the signal bouncing off objects; IR does tend to reflect well, although the signal strength must be dropping signaificantly after every refelction.

I suspect now its just a matter of getting the frequency and/or duty cycle right. You could also try 2 LEDs in series, pointing in a slightly divergent manner to give you a wider coverage.

Regards,

Anand

[dhouston]

Are you sending single or multiple copies of the IR? Most of the receivers need to see multiple copies to set their AGC and receive threshold so most protocols send more than a single copy.

[Kamikaze47]

Excellent! Working perfectly now

Switching the transistor and LED around so that the transistor is sinking current, and changing the bias resistor to 1k did the trick (Thanks keithdoxey and ardhuru)

It now has pretty much the same range and capability as my regular TV remote.

Thanks very much to all for your help.

My next step is to get it working with my Receiver. Getting that working should be much smoother now tho. I can actually change the PWM frequency on the fly by writing to the appropriate registers, so even if my other equipment works on different frequencies it shouldn't be a problem.