40kHz Infrared Serial Modulation?

Well, TV remotes send some kind of data stream for the different buttons, but I don't recall how fast - the point being, the receiver can be made to respond reliably, in a reasonable amount of time - try just turning the 40 KHz on and off at your 1200 BPS rate, and see what you get!

Good Luck! Rich

I don't know if this helps, but I think the quality factor of the receiver will prohibit such high modulation frequency. Look at irDA spec for higher bitrates.

cheers - Henry

"redbrickhat" schrieb im Newsbeitrag news: snipped-for-privacy@g43g2000cwa.googlegroups.com...

The use of a 40+kHz carrier for IR commands is AFAIK solely to reduce the possibility of interference or false triggering from the ambient background and to allow several IR systems to co-exist in one place. It's much the same as the carrier in any AM radio which allows you to receive many different broadcasts.

Norm

In the Vishay TSOP32138 datasheet the Data Formats are for IR remote controls. Do you think that such an IR receiver could also handle RS-232 data?

For example, in the link below, the TX pin of a PIC's UART is NANDed directly to a 38kHz signal:

Wouldn't there be some problems with timing if the RS-232 data had a long line of "1" bits?

Thanks.

"RS-232 data" can't have "a long line of '1' bits". An asynchronous data stream has start bits and stop bits, which if the thing isn't terribly out of tolerance, will resynchronize on every character.

And, technically, "RS-232" defines signal levels and connectors, and doesn't say much, if anything, IIRC, about the data format.

Here's a lucky google hit:

Hope This Helps! Rich

it attempts to block a continuous carrier-only signal

look at the codes the receiver supports, then compare with say the vishay part mentioned below.

exhume monsieur Fourier, he'll tell you what will happen. there will be a bandpass filter after the AGC, centered on the carrier. as you reduce the duty cycle below 50%, the amplitude of the fundamental decreases, so your range reduces. reductio ad absurdum - at 0% duty cycle it definitely wont work.

I'm not familiar with that particular detector but most IR receiver chips have circuitry to block CW (continuous wave) modulation. I recently designed a vishay TSOP32138.

their constraints are:

- burst length should be 6 cycles per burst or longer - >= 158us

- after each burst which is between 6 cycles and 70 cycles, a gap time of at least 10 cycles (263us) is necessary

- For each burst which is longer than 1.8ms, a corresponding gap time is necessary at some time in the data stream. This gap time should have at least the same length as the burst.

HTH

cheers Terry

Hi!

How was your holiday? Mine was wonderful - I sat at home and didn't have to talk to any relatives. ;-P

Cheers! Rich

If you are using a UART on a micro controller, you can use software Manchester encoding of the packet to ensure no long runs of "1" occur.

I used the PWM output to produce a square wave (38kHz) sent continuously to a 4066 input. The TX data then enabled the switch each time a "1" occurred.

To ensure you receiving UART locks on to the signal send a header that ensures synchronization. Some preamble (0x55, 0x55 ...) followed by a sequence that ensures UART sync (0x33,0xcc,0x33,0xcc,0x33) then your data and checksum. (data and checksum are in Manchester format).

If you check out the 0x33,0xcc combination, you will find that the Uart will always be in synch before the last byte .

Your receiver algorithm then waits for either 33 or CC to be received. It then waits for a none CC or 33 to be received (this is first byte of data).

You send each byte a nibble at a time by taking each bit in your data word and transforming it to a "10: if the original bit was a "1" and a "01" if it was a "0". The maximum length of "1" or "0" you can now have is 2 bit periods.

--

Kind Regards

David Huisman General Manager

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Gidday Mate,

glad to hear it. my hols were pretty good. spent xmas day with family, but luckily had the rest of the time just with Ruthy. Nice and relaxing. Its pretty hot though. I think I need a trip to the beach.

just got back from a long road trip to pick up my daughter; had an excellent time in Wellington, much great (and spicy) food was consumed, and saturday was a very big night (sunday was a very bad day :). First time I've drunk more than one beer in at least 6 months (I am always driving....)

Alas, my latest pcb just turned up, so the next few days will be hunched over the binocular microscope :(

charging by the hour :)

Kia Kaha, Terry

wot Rich said.

Hi Rich.

Cheers Terry

"redbrickhat" wrote in news: snipped-for-privacy@g43g2000cwa.googlegroups.com:

Can you use a different protocol aside ASK?

It might be worthwhile to look for an IRDA transceiver like

A standard SIR (serial infrared = RS232) transceiver should easily be able to handle 1200 bit/s.

Regards Volker