LED as detector for high speed link

Hi

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf

If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude. However, I need a large amplitude, to be able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a white LED (to cover the entire spectrum of the RED LED detector), a big one, and driving it with a lot of current, to get sufficient photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the responsivity wavelength, so that is why I use a white LED to be sure wavelenghts overlap

I will drive the emitter LED with high current, and then have a sufficient low load resistor for the red detector LED to have high bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf

Cheers

Klaus

 

[Cydrome Leader]

klaus.kragelund@gmail.com wrote:

Hi

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf

If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude. However, I need a large amplitude, to be able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a white LED (to cover the entire spectrum of the RED LED detector), a big one, and driving it with a lot of current, to get sufficient photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the responsivity wavelength, so that is why I use a white LED to be sure wavelenghts overlap

I will drive the emitter LED with high current, and then have a sufficient low load resistor for the red detector LED to have high bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf

I suspect you'll run into problems. White LEDs use a phosphor to convert
blue light to white. There will likely be a persistence issue, not unlike
CRTs or florescent light bulbs. So, to be able to transmit data in the
1Mhz range, the rise and decay time of that phosphor they use better be
really, really short. IR seems to be the norm for data transmission with
LEDs.

 

[Lasse Langwadt Christense]

tirsdag den 21. maj 2019 kl. 01.33.38 UTC+2 skrev Cydrome Leader:

klaus.kragelund@gmail.com wrote:
Hi

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf

If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude. However, I need a large amplitude, to be able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a white LED (to cover the entire spectrum of the RED LED detector), a big one, and driving it with a lot of current, to get sufficient photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the responsivity wavelength, so that is why I use a white LED to be sure wavelenghts overlap

I will drive the emitter LED with high current, and then have a sufficient low load resistor for the red detector LED to have high bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf

I suspect you'll run into problems. White LEDs use a phosphor to convert
blue light to white. There will likely be a persistence issue, not unlike
CRTs or florescent light bulbs. So, to be able to transmit data in the
1Mhz range, the rise and decay time of that phosphor they use better be
really, really short. IR seems to be the norm for data transmission with
LEDs.

https://books.google.dk/books?id=xR8uDwAAQBAJ&pg=PA449&lpg=PA449&dq=white+led+slow+phosfor&source=bl&ots=k7rVDUHoDo&sig=ACfU3U0oTbJQZwhXZN90ghs5k0GcpPKmvA&hl=da&sa=X&ved=2ahUKEwi2_r_ynKviAhVPJlAKHUHjCF0Q6AEwCHoECAcQAQ#v=onepage&q=white%20led%20slow%20phosfor&f=false

 

[Klaus Kragelund]

I cannot add circuitry to the detector side, since needs to be low cost

Cheers

Klaus

 

[John Larkin]

On Mon, 20 May 2019 23:33:33 +0000 (UTC), Cydrome Leader
<presence@MUNGEpanix.com> wrote:

klaus.kragelund@gmail.com wrote:
Hi

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf

If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude. However, I need a large amplitude, to be able to detect bit level with logic 3V. (so over 2.4V)

Why not amplify the LED current output, into a comparator maybe?

The price of the emitter is not relevant. So I was thinking to use a white LED (to cover the entire spectrum of the RED LED detector), a big one, and driving it with a lot of current, to get sufficient photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the responsivity wavelength, so that is why I use a white LED to be sure wavelenghts overlap

I will drive the emitter LED with high current, and then have a sufficient low load resistor for the red detector LED to have high bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf

I suspect you'll run into problems. White LEDs use a phosphor to convert
blue light to white. There will likely be a persistence issue, not unlike
CRTs or florescent light bulbs. So, to be able to transmit data in the
1Mhz range, the rise and decay time of that phosphor they use better be
really, really short. IR seems to be the norm for data transmission with
LEDs.

I tested some Cree white LEDs for speed, and they had nanosecond
response. The phosphors seem to be very fast.

But I'd guess that the best driver of a red LED is a red LED.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

There will likely be a persistence issue, not unlike
CRTs or florescent light bulbs. So, to be able to transmit data in the
1Mhz range, the rise and decay time of that phosphor they use better be
really, really short. IR seems to be the norm for data transmission with
LEDs.

Blue LEDs are pretty fast. I recently had reason to measure the temporal response of a 3200 lumen, 4000K white LED. With a 470-nm shortpass filter to separate the LED from the phosphor, it has a reasonable-looking step response with a TC of about 50 ns. With no filter, it's a drooly 300 ns.

Cheers

Phil Hobbs

 

[whit3rd]

On Monday, May 20, 2019 at 10:26:56 PM UTC-7, whit3rd wrote:

On Monday, May 20, 2019 at 2:48:13 PM UTC-7, klaus.k...@gmail.com wrote:

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

Why not just use an IeDA transmit/receive pair?

That's supposed to be ' IrDA', of course...

 

[whit3rd]

On Monday, May 20, 2019 at 2:48:13 PM UTC-7, klaus.k...@gmail.com wrote:

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)
....
If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude

Why not just use an IeDA transmit/receive pair? Speed is good, parts are available. And,
because it's a standard interface there are laptops and PDAs and laser printers that have it
already built in. A 'LED' might be tecnically capable of receiving, but it isn't
optimal (not a lot of receiver area to pick up light).

It's even easier to transformer-couple an interface; Ethernet magnetics
are mass produced and can outperform your target throughput handily, at quite reasonable
cost.

 

On Monday, May 20, 2019 at 8:09:25 PM UTC-4, Klaus Kragelund wrote:

I cannot add circuitry to the detector side, since needs to be low cost

Cheers

Klaus

Then it's going to be slow. LEDs make rotten photodiodes. Functional,
but just.

I tried it years ago. But rather than dig for my notes, I just
measured two combinations.

LEDs nose-to-nose, clear cases, If = 11.2mA, Vr = 0V.

emitter 'detector' photocurrent
------- -------------- ------------
GaN green AlGaInP red 1.7uA
AlGaInP red same as emitter 62uA

That's actually not too bad. If we assume I
was lucky enough to couple 5mW optical, that's
12mA/W photocurrent, or about 2% as good as a
PIN diode.

Cheers,
James Arthur

 

[bitrex]

On 5/20/19 5:48 PM, klaus.kragelund@gmail.com wrote:

Hi

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf

If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude. However, I need a large amplitude, to be able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a white LED (to cover the entire spectrum of the RED LED detector), a big one, and driving it with a lot of current, to get sufficient photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the responsivity wavelength, so that is why I use a white LED to be sure wavelenghts overlap

I will drive the emitter LED with high current, and then have a sufficient low load resistor for the red detector LED to have high bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf

Cheers

Klaus

If the price of the emitter isn't relevant why not use a big tri-color
RGB LED. I'm assuming there is some kind of software on the receiver end
too, to transmit data back.

Run an "auto tune" test data sequence on the emitter side that cycles
around thru the area of the color palette where you figure the best
responsivity of the red LED is and have the receiver side communicate
back where the best data rate happens. Then save that for use with that
particular LED.

 

[piglet]

On 20/05/2019 10:48 pm, klaus.kragelund@gmail.com wrote:

Hi

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf

If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude. However, I need a large amplitude, to be able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a white LED (to cover the entire spectrum of the RED LED detector), a big one, and driving it with a lot of current, to get sufficient photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the responsivity wavelength, so that is why I use a white LED to be sure wavelenghts overlap

I will drive the emitter LED with high current, and then have a sufficient low load resistor for the red detector LED to have high bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf

Cheers

Klaus

My experience was that Red LED responds very badly to red but much
better to higher energy/shorter wavelength green or blue light. White
phosphors will only lose you efficiency and worsen timings.

Not sure what your detector circuit will be but I cannot see how you can
get 2.4V (and isn't that above the Vf?) output without some
amplification even if only a penny BC847.

piglet

 

[piglet]

On 21/05/2019 7:46 am, bitrex wrote:

On 5/20/19 5:48 PM, klaus.kragelund@gmail.com wrote:
Hi

For a test setup I am toying with an isolated interface where I need 1
Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an
indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf


If I use the same dirt cheap LED as transmitter I can get about 10kBit
with small amplitude. However, I need a large amplitude, to be able to
detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a
white LED (to cover the entire spectrum of the RED LED detector), a
big one, and driving it with a lot of current, to get sufficient
photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the
responsivity wavelength, so that is why I use a white LED to be sure
wavelenghts overlap
I will drive the emitter LED with high current, and then have a
sufficient low load resistor for the red detector LED to have high
bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is
there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf


Cheers

Klaus


If the price of the emitter isn't relevant why not use a big tri-color
RGB LED. I'm assuming there is some kind of software on the receiver end
too, to transmit data back.

Run an "auto tune" test data sequence on the emitter side that cycles
around thru the area of the color palette where you figure the best
responsivity of the red LED is and have the receiver side communicate
back where the best data rate happens. Then save that for use with that
particular LED.

Err...I don't think that would work. The colour palette is a human eye
kind of thing. Having Red and Green LEDs on may look to the eye as
yellow but it is still red and green photons and no yellow photons.

piglet

 

[George Herold]

On Tuesday, May 21, 2019 at 5:01:29 AM UTC-4, piglet wrote:

On 20/05/2019 10:48 pm, klaus.kragelund@gmail.com wrote:
Hi

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf

If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude. However, I need a large amplitude, to be able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a white LED (to cover the entire spectrum of the RED LED detector), a big one, and driving it with a lot of current, to get sufficient photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the responsivity wavelength, so that is why I use a white LED to be sure wavelenghts overlap

I will drive the emitter LED with high current, and then have a sufficient low load resistor for the red detector LED to have high bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf

Cheers

Klaus


My experience was that Red LED responds very badly to red but much
better to higher energy/shorter wavelength green or blue light. White
phosphors will only lose you efficiency and worsen timings.

Not sure what your detector circuit will be but I cannot see how you can
get 2.4V (and isn't that above the Vf?) output without some
amplification even if only a penny BC847.

piglet

That was my experience too. (But I was using it as a spad. Reverse biased)

Forrest Mims is an LED as detector 'expert'. I emailed with him once.
http://www.forrestmims.org/

George h.

 

[bitrex]

On 5/21/19 5:01 AM, piglet wrote:

On 20/05/2019 10:48 pm, klaus.kragelund@gmail.com wrote:
Hi

For a test setup I am toying with an isolated interface where I need 1
Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an
indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf


If I use the same dirt cheap LED as transmitter I can get about 10kBit
with small amplitude. However, I need a large amplitude, to be able to
detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a
white LED (to cover the entire spectrum of the RED LED detector), a
big one, and driving it with a lot of current, to get sufficient
photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the
responsivity wavelength, so that is why I use a white LED to be sure
wavelenghts overlap
I will drive the emitter LED with high current, and then have a
sufficient low load resistor for the red detector LED to have high
bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is
there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf


Cheers

Klaus


My experience was that Red LED responds very badly to red but much
better to higher energy/shorter wavelength green or blue light. White
phosphors will only lose you efficiency and worsen timings.

Indeed this all sounds so familiar from somewhere....

Not sure what your detector circuit will be but I cannot see how you can
get 2.4V (and isn't that above the Vf?) output without some
amplification even if only a penny BC847.

piglet

 

[bitrex]

On 5/21/19 11:38 AM, bitrex wrote:

On 5/21/19 10:48 AM, John Larkin wrote:
On Tue, 21 May 2019 02:46:54 -0400, bitrex <user@example.net> wrote:

On 5/20/19 5:48 PM, klaus.kragelund@gmail.com wrote:
Hi

For a test setup I am toying with an isolated interface where I need
1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an
indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf


If I use the same dirt cheap LED as transmitter I can get about
10kBit with small amplitude. However, I need a large amplitude, to
be able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a
white LED (to cover the entire spectrum of the RED LED detector), a
big one, and driving it with a lot of current, to get sufficient
photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the
responsivity wavelength, so that is why I use a white LED to be sure
wavelenghts overlap
I will drive the emitter LED with high current, and then have a
sufficient low load resistor for the red detector LED to have high
bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is
there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf


Cheers

Klaus


If the price of the emitter isn't relevant why not use a big tri-color
RGB LED. I'm assuming there is some kind of software on the receiver end
too, to transmit data back.

Run an "auto tune" test data sequence on the emitter side that cycles
around thru the area of the color palette where you figure the best
responsivity of the red LED is and have the receiver side communicate
back where the best data rate happens. Then save that for use with that
particular LED.

All LEDs of a given part number will have about the same spectral
response, so he only has to figure that out once.



In the case of real bargain-basement LEDs I'm not sure there are any
guarantees of that. When you buy a bag of cheap LEDs from China their
characteristics are all over the place and stuff like forward voltage
vs. current varies wildly.

I tried one time to test a bag full and there's no nice bell curve to be
found on IV parameters of parts like that; all the good shit that can be
parameter-matched has been pulled by the mfgr already to make e.g. those
LED christmas lights strings where the LEDs can be run in parallel with
a single current-limiting resistor for the string because all the LEDs
in the set have matched forward voltages.

Perhaps spectral response would be the one thing that would be invariant
regardless but doesn't seem to apply to anything else at that price point.

Some fancy-schmancy Osram red LED where the LED in question actually has
a datasheet perhaps but at the "dirt cheap" end...datasheet? What's a
datasheet?

 

[bitrex]

On 5/21/19 10:48 AM, John Larkin wrote:

On Tue, 21 May 2019 02:46:54 -0400, bitrex <user@example.net> wrote:

On 5/20/19 5:48 PM, klaus.kragelund@gmail.com wrote:
Hi

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf

If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude. However, I need a large amplitude, to be able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a white LED (to cover the entire spectrum of the RED LED detector), a big one, and driving it with a lot of current, to get sufficient photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the responsivity wavelength, so that is why I use a white LED to be sure wavelenghts overlap

I will drive the emitter LED with high current, and then have a sufficient low load resistor for the red detector LED to have high bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf

Cheers

Klaus


If the price of the emitter isn't relevant why not use a big tri-color
RGB LED. I'm assuming there is some kind of software on the receiver end
too, to transmit data back.

Run an "auto tune" test data sequence on the emitter side that cycles
around thru the area of the color palette where you figure the best
responsivity of the red LED is and have the receiver side communicate
back where the best data rate happens. Then save that for use with that
particular LED.

All LEDs of a given part number will have about the same spectral
response, so he only has to figure that out once.

In the case of real bargain-basement LEDs I'm not sure there are any
guarantees of that. When you buy a bag of cheap LEDs from China their
characteristics are all over the place and stuff like forward voltage
vs. current varies wildly.

I tried one time to test a bag full and there's no nice bell curve to be
found on IV parameters of parts like that; all the good shit that can be
parameter-matched has been pulled by the mfgr already to make e.g. those
LED christmas lights strings where the LEDs can be run in parallel with
a single current-limiting resistor for the string because all the LEDs
in the set have matched forward voltages.

Perhaps spectral response would be the one thing that would be invariant
regardless but doesn't seem to apply to anything else at that price point.

 

[bitrex]

On 5/21/19 4:56 AM, piglet wrote:

On 21/05/2019 7:46 am, bitrex wrote:
On 5/20/19 5:48 PM, klaus.kragelund@gmail.com wrote:
Hi

For a test setup I am toying with an isolated interface where I need
1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an
indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf


If I use the same dirt cheap LED as transmitter I can get about
10kBit with small amplitude. However, I need a large amplitude, to be
able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a
white LED (to cover the entire spectrum of the RED LED detector), a
big one, and driving it with a lot of current, to get sufficient
photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the
responsivity wavelength, so that is why I use a white LED to be sure
wavelenghts overlap
I will drive the emitter LED with high current, and then have a
sufficient low load resistor for the red detector LED to have high
bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is
there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf


Cheers

Klaus


If the price of the emitter isn't relevant why not use a big tri-color
RGB LED. I'm assuming there is some kind of software on the receiver
end too, to transmit data back.

Run an "auto tune" test data sequence on the emitter side that cycles
around thru the area of the color palette where you figure the best
responsivity of the red LED is and have the receiver side communicate
back where the best data rate happens. Then save that for use with
that particular LED.

Err...I don't think that would work. The colour palette is a human eye
kind of thing. Having Red and Green LEDs on may look to the eye as
yellow but it is still red and green photons and no yellow photons.

piglet

Dunno what the human eye response has to do with anything a red LED used
as photodiode should be sensitive in some amount to wavelengths shorter
than red, into the ultraviolet I suppose.

IR photodidoe has its junction designed to respond best in the IR but
when using e.g. red LED junction in a clear envelope as a photo-diode
are there any guarantees that it will suck the least in response to a
single wavelength in the area of red as opposed to some combination of
the lower energy photos and higher?

 

[John Larkin]

On Tue, 21 May 2019 02:46:54 -0400, bitrex <user@example.net> wrote:

On 5/20/19 5:48 PM, klaus.kragelund@gmail.com wrote:
Hi

For a test setup I am toying with an isolated interface where I need 1 Mbit speed if possible

The receiver is a dirt cheap red LED: (which is also used as an indicator when the link is not active)

https://dammedia.osram.info/media/resource/hires/osram-dam-2493888/LH%20R974.pdf

If I use the same dirt cheap LED as transmitter I can get about 10kBit with small amplitude. However, I need a large amplitude, to be able to detect bit level with logic 3V. (so over 2.4V)

The price of the emitter is not relevant. So I was thinking to use a white LED (to cover the entire spectrum of the RED LED detector), a big one, and driving it with a lot of current, to get sufficient photon level at the red LED to have both high speed and logic IO level

An LED often have a different emission wavelength than the responsivity wavelength, so that is why I use a white LED to be sure wavelenghts overlap

I will drive the emitter LED with high current, and then have a sufficient low load resistor for the red detector LED to have high bandwidth (1MHz)

But, is this a good idea? Will I be overdriving the detector LED, is there some kind of saturation effect?

For the setup, I could use Win Hills 200A pulser:

https://www.dropbox.com/sh/svr7q23agwuvtat/AABdQSJq4d-7Qye96NLCCb9pa?dl=0&preview=200A-LED-pulse.pdf

Cheers

Klaus


If the price of the emitter isn't relevant why not use a big tri-color
RGB LED. I'm assuming there is some kind of software on the receiver end
too, to transmit data back.

Run an "auto tune" test data sequence on the emitter side that cycles
around thru the area of the color palette where you figure the best
responsivity of the red LED is and have the receiver side communicate
back where the best data rate happens. Then save that for use with that
particular LED.

All LEDs of a given part number will have about the same spectral
response, so he only has to figure that out once.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Mon, 20 May 2019 22:53:42 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

On Monday, May 20, 2019 at 8:09:25 PM UTC-4, Klaus Kragelund wrote:
I cannot add circuitry to the detector side, since needs to be low cost

Cheers

Klaus

Then it's going to be slow. LEDs make rotten photodiodes. Functional,
but just.

I tried it years ago. But rather than dig for my notes, I just
measured two combinations.

LEDs nose-to-nose, clear cases, If = 11.2mA, Vr = 0V.

emitter 'detector' photocurrent
------- -------------- ------------
GaN green AlGaInP red 1.7uA
AlGaInP red same as emitter 62uA

That's actually not too bad. If we assume I
was lucky enough to couple 5mW optical, that's
12mA/W photocurrent, or about 2% as good as a
PIN diode.

Cheers,
James Arthur

The target is awfully small, so most of the photons miss. I bet a lens
would help a lot.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Lasse Langwadt Christense]

tirsdag den 21. maj 2019 kl. 16.46.30 UTC+2 skrev John Larkin:

On Mon, 20 May 2019 22:53:42 -0700 (PDT), dagmargoodboat@yahoo.com
wrote:

On Monday, May 20, 2019 at 8:09:25 PM UTC-4, Klaus Kragelund wrote:
I cannot add circuitry to the detector side, since needs to be low cost

Cheers

Klaus

Then it's going to be slow. LEDs make rotten photodiodes. Functional,
but just.

I tried it years ago. But rather than dig for my notes, I just
measured two combinations.

LEDs nose-to-nose, clear cases, If = 11.2mA, Vr = 0V.

emitter 'detector' photocurrent
------- -------------- ------------
GaN green AlGaInP red 1.7uA
AlGaInP red same as emitter 62uA

That's actually not too bad. If we assume I
was lucky enough to couple 5mW optical, that's
12mA/W photocurrent, or about 2% as good as a
PIN diode.

Cheers,
James Arthur

The target is awfully small, so most of the photons miss. I bet a lens
would help a lot.

use a laser?