08M - Infrared output at 36KHz or 56KHz?

[pma32904]

Any thoughts on generating IR out at frequencies other than 38KHz with an 08M? I know Hippy has some ideas on line for Infrain work-around that might work on the receive side with the correct demodulator.

Only thing I can figure on the transmit side is to use pwmout to get the carrier frequency and they use another output to modulate the carrier through a FET or external mixer. I don't know if serout at an appropriate baud rate could be used.

Paul

 

[hippy]

You can simply modulate any LED by connecting it with an appropriate R between the PWMOUT pin and any other output pin. You'd only need more complex gating to drive more current through the LED.

It should be possible to modulate the IR LED with a SEROUT stream to a receiver of the same carrier frequency and read in with SERIN, but I haven't tried that.

 

[manuka]

Why the need? The 3 terminal "do everything" receiver units are cheap & tuned 38-42kHz. Freqs. hence well out from this may be a hassles to decode.

 

[pma32904]

Short story is I bought some IR demodulators which ended up being 36KHz. Although they worked with a Sony remote, the range with an 08M doing infraout was quite short. Also found that the lowest priced IR demodulators available to me were 56KHz. So I was naturally curious to see if I could do a work-around for 36/56 KHz. Perhaps more trouble than it's worth, but also a learning opportunity.

Paul

 

[pma32904]

Perhaps the internal oscillator calibration could be tweaked to shift 38KHz to 36Khz, assuming I do not need any other time critical functions? Thoughts?

 

[pma32904]

Of course, downloading of a new program could become problematic! Perhaps this is not worth the trouble...

 

[hippy]

I'm not sure that simply switching up to 56kHz modulation is going to give any increased range. It would probably be better and simpler overall to focus your energies on boosting the output signal ( and thus range ) from INFRAOUT and sticking with the standard components and INFRAIN/INFRAOUT commands.

 

[pma32904]

Sorry, I wasn't clear. I believe that with the 08M infraout sending at 38KHz and a demodulator tuned for 36KHz that the range was reduced because the TX & RX are not on the same frequency.

Different topic - 56KHz demods are the least expensive here. IF I had to go to the trouble of changing the infraout from 38KHz (standard) to 36KHz (to get decent range with 36KHz demod), why not change infraout to 56KHz and use really cheap 56KHz demod.

Hope that helps sort it out.

Paul

 

[hippy]

My mistake. I think it would be worth the extra cost to go to 38kHz demodulators in saving the effort in trying to go to 56kHz modulation.

If you've got a 56kHz IR LED it's always worth experimenting to see if a SERIN/SEROUT does work with a 56kHz demodulator.

 

[pma32904]

Perhaps I'll give this a try (56KHz IR modulation), as a learning exercise.

Thanks for the comments, etc.
Paul

 

[manuka]

It really relates to how many you need. For a small project I'd say the normal 38kHz decoders will win hands down, as they're pretty cheap in the right prices (~US$ 2-3).

What ranges do you need ? We've managed overdriving (& even parallel connecting) of IR LEDs & get 5-10m indoors daytime, with up to 50m outdoors at night. Considered a small lens to focus at the receiver as well? How about a tube to restrict stray IR sources?

As Hippy mentions, the 08M has such enhanced IR Tx/Rx features that dismissing them is really pretty futile! Stan





Edited by - manuka on 17/05/2007 19:54:30

 

[pma32904]

I agree with the points made. Problem is I ended up with a quantity of these 36KHz IR demodulators. In a previous application, I didn't even notice the range reduction for being off 38KHz. That was with a knock-off Sony remote.

This time around, I did notice a significant range reduction using the 08M with a FET driving the IR source, so plenty of drive. I suspect the 08M is slightly above 38KHz which would make the range/frequency issue worse.

For small quantities, sticking with 'standard' frequencies is easiest. However, now it's become an opportunity to dig and learn.

I'm already using an adaptation of Hippy's infrain to reduce the delay during IR receive. So, the learning continues...

 

[hippy]

As you've got the 38kHz demodulators it would be worth experimenting with CALIBFREQ to push the PICAXE oscillator up a notch or two while using a 36kHZ IR LED.

It might cause some problems with download, but a power-off then back on when the download pop-up appears should solve that, and a "PAUSE 2000" as the first line of code will also help.

 

[manuka]

Hippy- clever idea! The swing might just do it. Of course all manner of other problems may then emerge, but ...