NEC(?) IR remote control protocol

I want to decode the output from a remote control handset that uses what
some call the "NEC" protocol, reference:
http://www.xs4all.nl/~sbp/knowledge/ir/nec.htm

Not sure if "NEC" is the official name for it, as Googling for that does not
get many results.

It's a very simple protocol so I can write the decoding source from scratch,
but if there is some around already I'd be grateful of the time-saving, plus
any extra robustness that it might have over my attempts

FWIW I'm targetting a PIC12F629, but code for any microcontroller (assembler
or C) would be great, thanks.

Jim

Jim,

This stuff easily fits into 12C508. I do it quite a bit for a client.
Because of this, I can't give you the software. You can buy cheap chips
(12cxxx and 16cxxx based) from him if you need a quick solution. You can
get them from www.infraredremote.com. Done properly you can even get by
with the internal 4.0MHz RC oscillator.

Other than that, you will want to download the datasheet from a TSOP1238
from Vishay. You'll need to compensate for the pulse stretching and pulse
width distortions cause by modern IR receiver internal AGC and filter
circuits.

Noel

Jim wrote:

> I want to decode the output from a remote control handset that uses what
> some call the "NEC" protocol, reference:
> http://www.xs4all.nl/~sbp/knowledge/ir/nec.htm
>
> Not sure if "NEC" is the official name for it, as Googling for that does
> not get many results.
>
> It's a very simple protocol so I can write the decoding source from
> scratch, but if there is some around already I'd be grateful of the
> time-saving, plus any extra robustness that it might have over my attempts
>
>
> FWIW I'm targetting a PIC12F629, but code for any microcontroller
> (assembler or C) would be great, thanks.
>
> Jim

--
Noel's Lab
www.noels-lab.com
Chips, firmware, circuits and embedded systems

"Noel Henson" <> wrote in message
news:jlcYb.27040$. net...
> Jim,
>
> This stuff easily fits into 12C508. I do it quite a bit for a client.
> Because of this, I can't give you the software. You can buy cheap chips
> (12cxxx and 16cxxx based) from him if you need a quick solution. You can
> get them from www.infraredremote.com. Done properly you can even get by
> with the internal 4.0MHz RC oscillator.
>
> Other than that, you will want to download the datasheet from a TSOP1238
> from Vishay. You'll need to compensate for the pulse stretching and pulse
> width distortions cause by modern IR receiver internal AGC and filter
> circuits.
>
> Noel
>
> Jim wrote:

Many thanks for the info, Noel. In fact I need to use a PIC12F629 as it's
got other work to do as well as the decoding. It's a great chip for our
application - internal 8MHz oscillator with +/-1% accuracy or so and runs ok
from 3.3V. I don't think it costs much more than the gold ol' 12C508.

In fact, I've already got an IR receiver module (actually a Hero Electronics
HIM702HM, as it was easier and cheaper to get hod of than a Vishay for me at
the time). The output from it looks fine after some crude distance/obstacle
testing, so I'm ready to start coding. Just didn't want to rewrite the wheel
if someone has already done it and it's available.

Thanks too for the head-up re pulse stretching and distortions. That's
exactly the kind of thing I'm worried I'll miss if I write the code myself.
If I do my own code, I'll build in some slack for those possibilities.

Jim

On Tue, 17 Feb 2004 09:26:17 -0000, "Jim" <> wrote:

>"Noel Henson" <> wrote in message
>news:jlcYb.27040$ .net...
>> Jim,
>>
>> This stuff easily fits into 12C508. I do it quite a bit for a client.
>> Because of this, I can't give you the software. You can buy cheap chips
>> (12cxxx and 16cxxx based) from him if you need a quick solution. You can
>> get them from www.infraredremote.com. Done properly you can even get by
>> with the internal 4.0MHz RC oscillator.
>>
>> Other than that, you will want to download the datasheet from a TSOP1238
>> from Vishay. You'll need to compensate for the pulse stretching and pulse
>> width distortions cause by modern IR receiver internal AGC and filter
>> circuits.
>>
>> Noel
>>
>> Jim wrote:
>
>Many thanks for the info, Noel. In fact I need to use a PIC12F629 as it's
>got other work to do as well as the decoding. It's a great chip for our
>application - internal 8MHz oscillator with +/-1% accuracy or so and runs ok
>from 3.3V. I don't think it costs much more than the gold ol' 12C508.

Internal osc is 4MHz, not 8MHz.

"Mike Harrison" <> wrote in message
news:...
> On Tue, 17 Feb 2004 09:26:17 -0000, "Jim" <> wrote:
>
> >"Noel Henson" <> wrote in message
> >news:jlcYb.27040$ .net...
> >> Jim,
> >>
> >> This stuff easily fits into 12C508. I do it quite a bit for a client.
> >> Because of this, I can't give you the software. You can buy cheap chips
> >> (12cxxx and 16cxxx based) from him if you need a quick solution. You
can
> >> get them from www.infraredremote.com. Done properly you can even get by
> >> with the internal 4.0MHz RC oscillator.
> >>
> >> Other than that, you will want to download the datasheet from a
TSOP1238
> >> from Vishay. You'll need to compensate for the pulse stretching and
pulse
> >> width distortions cause by modern IR receiver internal AGC and filter
> >> circuits.
> >>
> >> Noel
> >>
> >> Jim wrote:
> >
> >Many thanks for the info, Noel. In fact I need to use a PIC12F629 as it's
> >got other work to do as well as the decoding. It's a great chip for our
> >application - internal 8MHz oscillator with +/-1% accuracy or so and runs
ok
> >from 3.3V. I don't think it costs much more than the gold ol' 12C508.
>
> Internal osc is 4MHz, not 8MHz.
>

You're right of course. Thanks for the correction.

- Jim

Jim wrote:

> "Noel Henson" <> wrote in message
> news:jlcYb.27040$. net...
>> Jim,
>>
>> This stuff easily fits into 12C508. I do it quite a bit for a client.
>> Because of this, I can't give you the software. You can buy cheap chips
>> (12cxxx and 16cxxx based) from him if you need a quick solution. You can
>> get them from www.infraredremote.com. Done properly you can even get by
>> with the internal 4.0MHz RC oscillator.
>>
>> Other than that, you will want to download the datasheet from a TSOP1238
>> from Vishay. You'll need to compensate for the pulse stretching and pulse
>> width distortions cause by modern IR receiver internal AGC and filter
>> circuits.
>>
>> Noel
>>
>> Jim wrote:
>
> Many thanks for the info, Noel. In fact I need to use a PIC12F629 as it's
> got other work to do as well as the decoding. It's a great chip for our
> application - internal 8MHz oscillator with +/-1% accuracy or so and runs
> ok from 3.3V. I don't think it costs much more than the gold ol' 12C508.
>
> In fact, I've already got an IR receiver module (actually a Hero
> Electronics HIM702HM, as it was easier and cheaper to get hod of than a
> Vishay for me at the time). The output from it looks fine after some crude
> distance/obstacle testing, so I'm ready to start coding. Just didn't want
> to rewrite the wheel if someone has already done it and it's available.
>
> Thanks too for the head-up re pulse stretching and distortions. That's
> exactly the kind of thing I'm worried I'll miss if I write the code
> myself. If I do my own code, I'll build in some slack for those
> possibilities.
>
> Jim

Jim,

The BEST way to test your code is to use one of the outputs as a temporary
test signal. While using a scope or, preferably a logic analyzer, you can
monitor the input from the receiver and the test signal. Have the test
signal Change state to show the start and stop time of your timing
windows, that way you can make sure that you are sampling in the center of
the window. Or, if you're using an interrupt-on-change function along with
a timer, you can use the test signal to show timeouts.

One of the easiest ways to decode on the 629 is to use the interrupt pin
set for any edge. Use a timer to measure the time between the edges. You
can then use a simple 'within-range' function or subroutine to determine
what the bits are and if they are valid.

Have fun!

Noel

--
Noel's Lab
www.noels-lab.com
Chips, firmware, circuits and embedded systems

"Noel Henson" <> wrote in message
news:lKqYb.27165$. net...
<snip>
> Jim,
>
> The BEST way to test your code is to use one of the outputs as a temporary
> test signal. While using a scope or, preferably a logic analyzer, you can
> monitor the input from the receiver and the test signal. Have the test
> signal Change state to show the start and stop time of your timing
> windows, that way you can make sure that you are sampling in the center of
> the window. Or, if you're using an interrupt-on-change function along with
> a timer, you can use the test signal to show timeouts.
>
> One of the easiest ways to decode on the 629 is to use the interrupt pin
> set for any edge. Use a timer to measure the time between the edges. You
> can then use a simple 'within-range' function or subroutine to determine
> what the bits are and if they are valid.
>
> Have fun!
>
> Noel
>
> --
> Noel's Lab
> www.noels-lab.com
> Chips, firmware, circuits and embedded systems

Hi Noel,

Thank you for more of your tips; it's much appreciated. I will do as you
suggest, using an interrupt-on-change from the input pin plus a timer, with
the provisos you've mentioned. A simple state machine should be sufficient
hopefully for the command decoding.

As an aside, I really enjoy coding towards this kind of task, but thought I
should check there isn't already some free source code out there first!

Jim

Jim wrote:

> "Noel Henson" <> wrote in message
> news:lKqYb.27165$. net...
> <snip>
>> Jim,
>>
>> The BEST way to test your code is to use one of the outputs as a
>> temporary test signal. While using a scope or, preferably a logic
>> analyzer, you can monitor the input from the receiver and the test
>> signal. Have the test signal Change state to show the start and stop time
>> of your timing windows, that way you can make sure that you are sampling
>> in the center of the window. Or, if you're using an interrupt-on-change
>> function along with a timer, you can use the test signal to show
>> timeouts.
>>
>> One of the easiest ways to decode on the 629 is to use the interrupt pin
>> set for any edge. Use a timer to measure the time between the edges. You
>> can then use a simple 'within-range' function or subroutine to determine
>> what the bits are and if they are valid.
>>
>> Have fun!
>>
>> Noel
>>
>> --
>> Noel's Lab
>> www.noels-lab.com
>> Chips, firmware, circuits and embedded systems
>
> Hi Noel,
>
> Thank you for more of your tips; it's much appreciated. I will do as you
> suggest, using an interrupt-on-change from the input pin plus a timer,
> with the provisos you've mentioned. A simple state machine should be
> sufficient hopefully for the command decoding.
>
> As an aside, I really enjoy coding towards this kind of task, but thought
> I should check there isn't already some free source code out there first!
>
>
> Jim

You're a quick study. It looks like you'll do just fine.
Noel


--
Noel's Lab
www.noels-lab.com
Chips, firmware, circuits and embedded systems