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'[EE]: IR controller design problem'
2000\11\08@223849 by William

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face
Dear All,

I am doing a porject on 4x4 keypad IR controller using PIC16F84.
Besides of doing 4x4 keypad scaning, I am need to find out how to
do IR signal transmitting. Is there any good side talking about IR
signal
transmitting.

Is that IR signals need to modulated in 30 - 40khz, so that it won't
interference with tube light, or sun light??? Any modulation scheme easy

to implement?

----------------------

I use my PIC (one I/O as output) to drive my IR LED with 220 ohm R.
Then,
I output high, and measures the current, just 18mA. Can this be the
problem
(weak current) and LED emmit less signal???

----------------------

One more problem is, my program is send out pulse (High) for 7uS and
space (Low) for 20uS, and
make a full one cycle of about 37khz contineous pulse signal. For
receiver, I just used normal IR
receiver (3 pin). I didn't add any circuit at the output pin of IR
receiver. I probe the receiver ouput
pin, and run my PIC. On my scope, I can see pulses quite okay, distance
between Tx and Rx is about
10cm. Then, if further, then, no pulses display on scope!!!

Oh, what's wrong??? Transmitter problem or receiver problem? Then, I
take my TV IR controller, 2m
apart from the IR receiver, press any keys, scope also display the
received signals clearly!!! I can't just
design a controller that only can receive 10cm signals!!!

Some one, expert in IR, please give me your advice, I really need help.


Thank you.


Warmset regards,

William

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2000\11\09@003211 by Jinx

face picon face
> Is that IR signals need to modulated in 30 - 40khz, so that it won't
> interference with tube light, or sun light??? Any modulation scheme
> easy to implement?

3-terminal receivers like the Sharp ISU60 are tuned to 38kHz and have
a built-in daylight filter. A continuous 38kHz stream of IR pulses will
give a continuous low output. In the absence of a signal the output is
high. I use this system for a broken beam application.

A 555 or gated CMOS oscillator made from a 4001 or 4011 can be
used as a data-to-38kHz convertor

> I use my PIC (one I/O as output) to drive my IR LED with 220 ohm R.
> Then, I output high, and measures the current, just 18mA. Can this be
> the problem (weak current) and LED emmit less signal???

220R sounds high. IR LEDs can take many amps IF you use short pulses,
ie in the microseconds and in this case you can use down to 1 ohm. BUT
do not attempt this with a PIC pin. You must have a fast high current
driver, such as a Zetex transistor (eg ZTX649 to ZTX751 range) to
get this sort of power to an IR LED. Other types such as 2N2222 or
BC549s do not switch current fast enough. You MUST keep pulses
short. Doing so will get you many metres, even outdoors. To improve
reception, put the receiver down a tube to minimise external light getting
to it. Light bulbs do have an effect on the receivers, but hardly at all
when
the receiver is shaded from them

> One more problem is, my program is send out pulse (High) for 7uS
> and space (Low) for 20uS, and make a full one cycle of about 37khz
> contineous pulse signal. For receiver, I just used normal IR receiver
> (3 pin). I didn't add any circuit at the output pin of IR receiver. I
probe
{Quote hidden}

As above, you are not getting enough power to the LED. Have a look
inside your TV remote and you will find it uses a low value resistor and/or
an extra LED. It is also advisable to put a reservoir capacitor (>100uF) to
supply the instantaneous power needed for short pulses. You should
also try to match the IR frequency (usually quoted around 950nm) of the
transmitter to the response of the receiver as best as you can. Depending
on the application, there are a range of beam angles for transmitter LEDs
and acceptance angles for receivers. If you want a narrow beam go for
perhaps a 15 degree LED, to flood an area go for a 100 degree. Same
thing for receivers

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2000\11\09@010718 by w. v. ooijen / f. hanneman

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> 3-terminal receivers like the Sharp ISU60 are tuned to 38kHz and have
> a built-in daylight filter. A continuous 38kHz stream of IR pulses will
> give a continuous low output. In the absence of a signal the output is
> high. I use this system for a broken beam application.

This is not true for TSOP and SFH 3-pin receivers: a continuous signal
rises the comparison treshold so eventually the output signal will be
noise. Hence a code like RC4 is needed that contains gaps. TSOP and SFH
receivers come in various versions (last 2 digits of the name), ranging
from 30 to 56 kHz.

Wouter

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2000\11\09@013703 by w. v. ooijen / f. hanneman

picon face
Take a look at the vishay / telefunken / temic documentation for the TSOP
IR receivers. Do you use an IR receiver? In that case you must stick to the
frequency for that device quite accurately (ideally stay within a %). The
output of an IR receiver is not the ~ 30 kHz signal, but the
AM-demodulation of it! And an IR-receiver can not cope with a continuous
input signal. Search the web for RC4 for a good code to use with IR.
Wouter

----------
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2000\11\09@014548 by William

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Hi, Mr w.v.oojien/f. hanneman.

Actually, my receiver is taken out from a spoilt remote electronic device,
and also my IR led, from its remote controller too.

My receiver is written HS38B on it, but I can't find spec. for this part.



"w. v. ooijen / f. hanneman" wrote:

> Take a look at the vishay / telefunken / temic documentation for the TSOP
> IR receivers. Do you use an IR receiver? In that case you must stick to the
> frequency for that device quite accurately (ideally stay within a %). The
> output of an IR receiver is not the ~ 30 kHz signal, but the
> AM-demodulation of it!

signal is not 30khz? Then is what??? I am a bit confuss right now.



> And an IR-receiver can not cope with a continuous
> input signal. Search the web for RC4 for a good code to use with IR.
> Wouter

RC4, is this a standard of a IR signal???

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2000\11\09@023400 by Jinx

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> Actually, my receiver is taken out from a spoilt remote electronic device,
> and also my IR led, from its remote controller too.

You said in your original post that you could see pulses. If you are
getting 0 to 5V pulses (not lower voltage analogue-type pulses that
need amplifying and squaring) and they don't fade away as the IR
keeps on coming, then all you need to do is make the transmitter
more powerful, as you also said that the receiver works OK with your
TV remote. Have a look in the electronic device you got the receiver
from and see if there are any signal conditioning components such
as amplifiers after the receiver. That should give you an idea of what
type of receiver it is.

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2000\11\09@040358 by William

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Hi, Jinx.

Thanks for your quick response. I think my receiving part, which connect
to probe is fine, coz when I pressed the TV remote a few time on same
button, they look quite even.

Then, I pressed my ir keypad, thing really a lot of deferrences. my
ir keypad output a burst of ~37khz pulse, and sometimes it output a
burst, but sometimes it output like 2 or 3 bursts.

If I go more more pulse, I output 5 pulse. The receiver look like this


     | | | | |
     | | | | |
     | | | | |
   --+-+-+-+-+----   signal out from pic16f84 to IR LRD

     +-------+
     |       |
     |       |
   --+       +-----   scope output

The scope output for my signals are really bad. But for TV remote,
the scope can display train of signals for TV remote signal.

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2000\11\09@063828 by Jinx

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part 1 3053 bytes content-type:text/plain; (decoded 7bit)

> to probe is fine, coz when I pressed the TV remote a few time on same
> button, they look quite even.
>
> Then, I pressed my ir keypad, thing really a lot of deferrences. my
> ir keypad output a burst of ~37khz pulse, and sometimes it output a
> burst, but sometimes it output like 2 or 3 bursts.
>
> The scope output for my signals are really bad. But for TV remote,
> the scope can display train of signals for TV remote signal.

I think the problem is that the IR signal is too weak and the receiver
may not be detecting it properly. If you are seeing a good signal
at the PIC pin and you aren't seeing it at the receiver then you'll
have to make the IR signal stronger. You need to do this anyway
to get past 10cm

Attached are suggestions for reasonably strong transmitters. You'll
certainly get a few metres with these. The 555 can source or sink
200mA so the LED can be high side or low side

Fig1 is a constant beam. Note that the power goes to the LED when
the output of the 555 is low, so the pulse train is high more than low.
This transmitter can be picked up 8 metres away by an IS1U60 if
a matched 5mm LED is used, less if a 3mm

Fig2a is a data-to-38kHz convertor. When Reset (pin4) goes low
the output is a steady low, so you need to put the LED as a low side
component. When Reset goes high, the oscillator is enabled and a
"block" of 38kHz will be sent from the LED. Note that the pulse train
is low more than high, the opposite of Fig1. To get more power you
can drive a ZTX649 directly with the 200mA available from the 555
and use multiple LEDs with smaller resistors. The ZTX649 is rated
at 1A, but there are other ZTXs rated for 3A. The main point about
them is that they are fast current switches and give good strong pulses
into the LEDs. In both circuits use a reservoir cap close to the LED/
resistor for best results. You will have to adjust the oscillator resistors
to get the correct frequency and pulse width for your components. Tune
it on the scope before attaching the LED to make sure you don't
over-power the LED. You could use the waveform of your TV remote
as a guide. Perhaps the best way might be to determine what range
you want and increase the pulse width until the receiver sees it. Work
out what the widest pulse width you can use is based on the power
dissipation of the LED. Except you probably don't know what the
LED you have is

The IS1U60 "inverts" the signal it receives. When 38kHz is present
the output is low. If your receiver does the same thing you'll need to
invert the data bits you send otherwise a "1" will cause the receiver
output to go low. Either that or invert the output of the receiver. The
IS1U60 will not work properly if a 100uF cap is not soldered directly
across its power supply pins. Without it the output is erratic, perhaps
you have the same problem

The HS38B might be a Honeywell device. I searched their site and it
said it had found 4 matches, but I couldn't find a data sheet


part 2 4493 bytes content-type:image/gif; (decode)


part 3 146 bytes
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