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Guest
Posted: Mon Feb 12, 2007 7:28 am
I've seen lots of schematics on the net for receiving signals
modulated at around 30-40kHz, but I'm trying to design a system that
will work at around the 1Mhz range. I've practically tried the
designs at those frequencies, but there seems to be a lot of
atenuation at higher frequencies. I've been told this is because the
photodiode acts like a cpaacitor when reverse biased, and that
capacitor causes attenuation with high frequencies. Is there any way
round that?

I know it must be possible because IRDA manages data rates of up to
4Mbps (although using a PPM system). I'm trying to achieve a data
rate or atround 500bps, using any standard as I'm designing
transmitter and receiver. Any suggestions?
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Tim Wescott
Posted: Mon Feb 12, 2007 1:01 pm
Guest
omattos@gmail.com wrote:
Quote:
I've seen lots of schematics on the net for receiving signals
modulated at around 30-40kHz, but I'm trying to design a system that
will work at around the 1Mhz range. I've practically tried the
designs at those frequencies, but there seems to be a lot of
atenuation at higher frequencies. I've been told this is because the
photodiode acts like a cpaacitor when reverse biased, and that
capacitor causes attenuation with high frequencies. Is there any way
round that?

I know it must be possible because IRDA manages data rates of up to
4Mbps (although using a PPM system). I'm trying to achieve a data
rate or atround 500bps, using any standard as I'm designing
transmitter and receiver. Any suggestions?

If IRDA has solved this problem already, why not use it? If not the

whole of IRDA, how about finding front-end designs for its receiver?

My knee-jerk reaction to this is to use a good fast PIN diode, and feed
it into a common-base transistor stage. So long as you use a modulation
method that can be AC coupled this should be pretty easy to do.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html
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RHRRC
Posted: Mon Feb 12, 2007 2:31 pm
Guest
On 12 Feb, 11:28, omat...@gmail.com wrote:
Quote:
I've seen lots of schematics on the net for receiving signals
modulated at around 30-40kHz, but I'm trying to design a system that
will work at around the 1Mhz range. I've practically tried the
designs at those frequencies, but there seems to be a lot of
atenuation at higher frequencies. I've been told this is because the
photodiode acts like a cpaacitor when reverse biased, and that
capacitor causes attenuation with high frequencies. Is there any way
round that?

I know it must be possible because IRDA manages data rates of up to
4Mbps (although using a PPM system). I'm trying to achieve a data
rate or atround 500bps, using any standard as I'm designing
transmitter and receiver. Any suggestions?

Have a look at the Vishay IR receiver modules at 455Khz. http://
www.vishay.com/ir-receiver-modules/
These will comfortably give you 10K+ bps. - they are cheap and easy.
Similar modules are available from others

Don't forget to drive the LED(s) properly - at these speeds the diode
capactance can become significant and you need to drive the LEDs on
and off. Sticking the LED(s) on a collector with a series R will not
do unless you are only looking for a short range.
Also, whilst you are playing around with any cicuitry, be aware of the
eye hazard of IRleds.
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Antony
Posted: Wed Feb 14, 2007 7:53 am
Guest
On Feb 12, 10:31 am, "RHRRC" <h.le...@connect-2.co.uk> wrote:
Quote:
On 12 Feb, 11:28, omat...@gmail.com wrote:

I've seen lots of schematics on the net for receiving signals
modulated at around 30-40kHz, but I'm trying to design a system that
will work at around the 1Mhz range. I've practically tried the
designs at those frequencies, but there seems to be a lot of
atenuation at higher frequencies. I've been told this is because the
photodiode acts like a cpaacitor when reverse biased, and that
capacitor causes attenuation with high frequencies. Is there any way
round that?

I know it must be possible because IRDA manages data rates of up to
4Mbps (although using a PPM system). I'm trying to achieve a data
rate or atround 500bps, using any standard as I'm designing
transmitter and receiver. Any suggestions?

Have a look at the Vishay IR receiver modules at 455Khz. http://www.vishay.com/ir-receiver-modules/
These will comfortably give you 10K+ bps. - they are cheap and easy.
Similar modules are available from others

Don't forget to drive the LED(s) properly - at these speeds the diode
capactance can become significant and you need to drive the LEDs on
and off. Sticking the LED(s) on a collector with a series R will not
do unless you are only looking for a short range.
Also, whilst you are playing around with any cicuitry, be aware of the
eye hazard of IRleds.


I always thought the eye hazards were minimal. After all, IR is what
is used in Laser Tag/MILES and its deemed safe in that application. I
don't see why it would be unsafe here.
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RHRRC
Posted: Wed Feb 14, 2007 5:16 pm
Guest
On 14 Feb, 11:53, "Antony" <ambu...@gmail.com> wrote:
Quote:
On Feb 12, 10:31 am, "RHRRC" <h.le...@connect-2.co.uk> wrote:





On 12 Feb, 11:28, omat...@gmail.com wrote:

I've seen lots of schematics on the net for receiving signals
modulated at around 30-40kHz, but I'm trying to design a system that
will work at around the 1Mhz range. I've practically tried the
designs at those frequencies, but there seems to be a lot of
atenuation at higher frequencies. I've been told this is because the
photodiode acts like a cpaacitor when reverse biased, and that
capacitor causes attenuation withhighfrequencies. Is there any way
round that?

I know it must be possible because IRDA manages data rates of up to
4Mbps (although using a PPM system). I'm trying to achieve a data
rate or atround 500bps, using any standard as I'm designing
transmitter and receiver. Any suggestions?

Have a look at the VishayIRreceiver modules at 455Khz. http://www.vishay.com/ir-receiver-modules/
These will comfortably give you 10K+ bps. - they are cheap and easy.
Similar modules are available from others

Don't forget to drive the LED(s) properly - at these speeds the diode
capactance can become significant and you need to drive the LEDs on
and off. Sticking the LED(s) on a collector with a series R will not
do unless you are only looking for a short range.
Also, whilst you are playing around with any cicuitry, be aware of the
eye hazard of IRleds.

I always thought the eye hazards were minimal. After all,IRis what
is used in Laser Tag/MILES and its deemed safe in that application. I
don't see why it would be unsafe here.- Hide quoted text -

- Show quoted text -

What makes you think the eye hazard is minimal.
What do others do to avoid eye hazard with IR?
A class 1 product is indeed not deemed a hazard (under normal
conditions).Class2 and upwards may be hazardous.
Start off with EN (or IEC) 60285. A reading and understanding of this
is imperative and has a legal enforcement.
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