Using LEDs as photovoltaics

[Rick C]

On Friday, November 8, 2019 at 5:38:18 AM UTC-5, Martin Brown wrote:

On 07/11/2019 20:43, Rick C wrote:
On Thursday, November 7, 2019 at 1:27:36 PM UTC-5, Clive Arthur
wrote:
On 07/11/2019 18:11, whit3rd wrote:

Well, my 'white' LED gives 2.2V open circuit and 10 or 20uA short
circuit (it's the last digit on my DVM flickering 1&2) when
illuminated with a single UV LED from a torch. I'm guessing a blue
LED receiver (ie without the phosphor) would do better.

Forest Mimms III as suggested by George H suggests that LEDs are
narrow band receivers, so I'm not sure why the UV LED works so well
as a source. It is partly visible with a sort of yellowish tinge.

I would not expect LEDs to be "narrow band". For a photon to be
absorbed it would need to have sufficient energy. That equates to
being short wavelength enough which is what George H said.

They are fairly narrow band with a typical FWHM of 50nm around their
nominal wavelength. You might get optimum performance with the emitter
wavelength slightly shorter than the detector. Possible for some "pure"
blues and greens these days.

It is a general rule that emitters at a particular frequency are also
good absorbers at that frequency when illuminated.

Are you suggesting that an LED is not responsive to shorter wavelengths than the wavelength they emit?

As others have pointed out the area of the receiving diode is rather
small so it will be hard to gather enough energy. The IV curve
should be fairly flat on both the current limited side and the
voltage limited side with the max power point in the knee of
intersection. Try reading the voltage under the load you will need.

I like JL's idea of a single compound blue LED with 12v nominal drop.

I like the idea of using some photocells, but the world is a strange place.

--

Rick C.

+ Get 1,000 miles of free Supercharging
+ Tesla referral code - https://ts.la/richard11209

 

On Fri, 8 Nov 2019 22:32:38 +1100, Chris Jones
<lugnut808@spam.yahoo.com> wrote:

On 07/11/2019 21:44, Clive Arthur wrote:
An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

[I can't use the packaged photovoltaic isolators/drivers, I need a bit
more distance.]

I have read that you should use the same colour for drive and sense,
which sounds reasonable.  I imagine that higher Vf LEDs produce more V,
but I'd need a few in series anyway so that doesn't really matter.

I tried a white power LED (just because I had one lying about) and
illuminating it with another gave me about 2V on my DMM, short circuit
current too small to measure without fiddling about.  Yes, I know the
yellow phosphor just gets in the way and wastes power, but it's a start.

I'll need to do some experimenting, but I'd like to narrow things down a
bit first.  I think the packaged photovoltaic isolators use IR LEDs, a
guess based on their Vf - would blue LEDs be better?  In any event,
being able to see it working would be advantageous in this application.

Cheers


Could you use one modulated IR LED (e.g. SFH 4725S), driving one BPW34
photodiode that feeds a small step-up transformer and rectifier? It will
not be suitable for turning the output voltage on or off quickly as the
smoothing cap after the rectifier will slow things down. You can also
have two photodiodes in anti-parallel for push-pull drive to the step-up
transformer but you'd have to illuminate them with two LEDs in anti-phase.

A photodiode is a current source in parallel with a diode, so if you
put it across an LC tank, you get a bunch of p-p AC, if that's worth
anything.

Lots of things would be possible except that you are probably working
with microamps of photocurrent.

Aren't there photofets?




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Fri, 8 Nov 2019 11:01:52 +0000, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

On 07/11/2019 23:46, John Larkin wrote:
snipped

Cree, and several other people, make "high voltage" multi-chip LEDs,
in white and blue and other colors, 12 to 48 volts. The 12v white ones
that I have look like welding torches.

Blue-to-blue 12 volts might work.

Thanks, I'll look into that. Not literally.

Cheers

I have a friend who designs, among other things, street lights, and he
gave me a few monster custom LEDs, about an inch square slab of
aluminum with an array of chips and phosphor. At full power, they are
literally dangerous to look at. They need a lot of heat sinking.

How far do you want to go between the chips? A light pipe might help.
Maybe you could make your own mega-fiber, just a piece of soft plastic
stuff.

Fill up a plastic tube with something else and make a giant step index
fiber!



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Rick C]

On Friday, November 8, 2019 at 9:11:05 AM UTC-5, Clive Arthur wrote:

On 08/11/2019 13:51, Rick C wrote:

snipped

I like the idea of using some photocells, but the world is a strange place.

Farnell and RS don't seem to sell anything suitable, which indicates
they're a bit hard to find. I suspect they'd be quite big too.

Solar cells hard to find??? Did you look at eBay? You can find hundreds in all sizes. I have some that are quite small. Heck, I have a little head swinging monkey toy from the dollar store that used a very small solar cell to power it. If you can't find a solar cell, you aren't trying.


> LEDs are easy to find, so if they work well enough...

That's the IF that hasn't been determined yet. You still don't know how much current you can pull before the voltage collapses. That's why I say the world is a strange place. I would find that information before I waste a bunch of time trying to optimize the color of the LED. I also wouldn't waste my time with a phosphor laden white LED.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[Clive Arthur]

On 08/11/2019 14:54, Rick C wrote:

On Friday, November 8, 2019 at 9:11:05 AM UTC-5, Clive Arthur wrote:
On 08/11/2019 13:51, Rick C wrote:

snipped

I like the idea of using some photocells, but the world is a strange place.

Farnell and RS don't seem to sell anything suitable, which indicates
they're a bit hard to find. I suspect they'd be quite big too.

Solar cells hard to find??? Did you look at eBay? You can find hundreds in all sizes. I have some that are quite small. Heck, I have a little head swinging monkey toy from the dollar store that used a very small solar cell to power it. If you can't find a solar cell, you aren't trying.

It would be part of a commercial product, so reliable, repeatable
available etc apply. I could hack something, but it's sort of obvious
that solar cells would work, so not worth trying unless they can be
found small enough and through proper channels. It's just to turn a
MOSFET on, so very little power.

LEDs are easy to find, so if they work well enough...

That's the IF that hasn't been determined yet. You still don't know how much current you can pull before the voltage collapses. That's why I say the world is a strange place. I would find that information before I waste a bunch of time trying to optimize the color of the LED. I also wouldn't waste my time with a phosphor laden white LED.

The white LED was all I had to hand, others to arrive soon, though I
since found a small SM green LED which will give 1.6V on the DVM (10M
IIRC) and 1.5V with 1M across it, so already in the right ballpark for a
few of these in series. This was illuminated with a green laser
pointer, a red one does nothing and a UV torch does very little, so it
looks like the wavelength can indeed be too short.

The white LED wasn't a waste of time - it showed me that I could get
usable output despite it being non-optimal and that further
investigation is warranted.

But my experiments are very, very ballpark at the moment, just enough to
convince me that it can be done fairly easily. I should find out more
next week.

Cheers
--
Clive

 

[Clive Arthur]

On 08/11/2019 15:37, jlarkin@highlandsniptechnology.com wrote:

<snip>

> Aren't there photofets?

Yes Optomos and similar. I've used them elsewhere to provide isolated
volt-free contacts.

Cheers
--
Clive

 

On Thu, 7 Nov 2019 10:44:33 +0000, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

An old abandoned requirement has re-surfaced...

If I wanted to use some series LEDs, illuminated by more LEDs to
generate a small amount of isolated power - say to turn on a MOSFET not
particularly quickly, say 10V at a few uA - what would be the best type?

[I can't use the packaged photovoltaic isolators/drivers, I need a bit
more distance.]

I have read that you should use the same colour for drive and sense,
which sounds reasonable. I imagine that higher Vf LEDs produce more V,
but I'd need a few in series anyway so that doesn't really matter.

I tried a white power LED (just because I had one lying about) and
illuminating it with another gave me about 2V on my DMM, short circuit
current too small to measure without fiddling about. Yes, I know the
yellow phosphor just gets in the way and wastes power, but it's a start.

I'll need to do some experimenting, but I'd like to narrow things down a
bit first. I think the packaged photovoltaic isolators use IR LEDs, a
guess based on their Vf - would blue LEDs be better? In any event,
being able to see it working would be advantageous in this application.

Cheers

OK, here's a goofy idea.

Couple some surface-mount right-angle LEDs on a PCB, using a 2-mode
lens (which I just invented in the shower)

https://www.dropbox.com/s/3t3wihqvxqc04rt/PV_Opto_2mode.JPG?raw=1

This is a double-convex lens in one axis and a TIR internal reflection
channel in another. The lens is just a plastic disk. It might even
work with a clear washer that has a small bolt hole in the middle.

There's probably a standard polycarb or acrylic washer like this
somewhere, for a penny maybe. Three blue LEDs would probably turn on a
low-threshold mosfet. Maybe even two.

Don't solvent wash the plastic lens. Install the lens after the board
is cleaned.

That may not be your geometry.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[whit3rd]

On Friday, November 8, 2019 at 7:51:20 AM UTC-8, Clive Arthur wrote:

... found a small SM green LED which will give 1.6V on the DVM (10M
IIRC) and 1.5V with 1M across it, so already in the right ballpark for a
few of these in series. This was illuminated with a green laser
pointer, a red one does nothing and a UV torch does very little, so it
looks like the wavelength can indeed be too short.

Photoelectric absorption has a sharp cliff in the light-below-threshold direction,
and a slower falloff slope in the light-above-threshold direction,
so you'd expect (due to random variation) green-driving-green to be
less reliable than blue-driving-green or shortwave-UV-driving longwave-UV.

Cree Royal Blue (450 nm) would be a good driver for Cree Blue (465 nm)
receiver, by that logic.

 

[George Herold]

On Friday, November 8, 2019 at 5:38:18 AM UTC-5, Martin Brown wrote:

On 07/11/2019 20:43, Rick C wrote:
On Thursday, November 7, 2019 at 1:27:36 PM UTC-5, Clive Arthur
wrote:
On 07/11/2019 18:11, whit3rd wrote:

Well, my 'white' LED gives 2.2V open circuit and 10 or 20uA short
circuit (it's the last digit on my DVM flickering 1&2) when
illuminated with a single UV LED from a torch. I'm guessing a blue
LED receiver (ie without the phosphor) would do better.

Forest Mimms III as suggested by George H suggests that LEDs are
narrow band receivers, so I'm not sure why the UV LED works so well
as a source. It is partly visible with a sort of yellowish tinge.

I would not expect LEDs to be "narrow band". For a photon to be
absorbed it would need to have sufficient energy. That equates to
being short wavelength enough which is what George H said.

They are fairly narrow band with a typical FWHM of 50nm around their
nominal wavelength. You might get optimum performance with the emitter
wavelength slightly shorter than the detector. Possible for some "pure"
blues and greens these days.

It is a general rule that emitters at a particular frequency are also
good absorbers at that frequency when illuminated.

As others have pointed out the area of the receiving diode is rather
small so it will be hard to gather enough energy. The IV curve
should be fairly flat on both the current limited side and the
voltage limited side with the max power point in the knee of
intersection. Try reading the voltage under the load you will need.

I like JL's idea of a single compound blue LED with 12v nominal drop.

--
Regards,
Martin Brown

 

[Clive Arthur]

I did some crude testing with Red, Green, Blue and UV LEDs.

All 1210 SMD 'high brightness' types from the same supplier.

One of each in series at their rated 20mA, then holding another of each
against each in turn, no air gap, switching in 1M as a load.

First thing to notice is how much brighter the green appears to be, yes
I know that's where the eye is most sensitive, but it does stand out
more than I expected. The red and blue appear about the same brightness
as each other, the UV emits a little visible violet.

Volts OC/Volts 1M load (OC is DVM impedance)

Receive -> Red Green Blue UV
Tx
Red 1.53/1.50 3m/0 0/0 0/0
Green 1.59/1.58 2.03/1.15 200m/20m 3m/2m
Blue 1.50/1.45 2.12/2.11 2.29/1.90 9m/2m
UV 1.42/63m 2.11/2.09 2.34/2.29 2.61/2.47

So Blue --> Green looks favourite, no better than UV --> Green but
easier to see.

If TX is longer wavelength than RX then nothing much, if TX is
considerably shorter than RX then weak. Best seems when TX is a little
shorter than RX as predicted by Martin Brown.

So five Green receivers gives me my 10V. Five Blue transmitters may
work with a gap, may need focussing, could use more powerful types.

Cheers
--
Clive

 

On Mon, 11 Nov 2019 12:48:25 +0000, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

I did some crude testing with Red, Green, Blue and UV LEDs.

All 1210 SMD 'high brightness' types from the same supplier.

One of each in series at their rated 20mA, then holding another of each
against each in turn, no air gap, switching in 1M as a load.

First thing to notice is how much brighter the green appears to be, yes
I know that's where the eye is most sensitive, but it does stand out
more than I expected. The red and blue appear about the same brightness
as each other, the UV emits a little visible violet.

I'm using one family of LEDs where at equal currents, green is dim,
orange is nice, and blue is blinding. Had to change some resistors.

Volts OC/Volts 1M load (OC is DVM impedance)

Receive -> Red Green Blue UV
Tx
Red 1.53/1.50 3m/0 0/0 0/0
Green 1.59/1.58 2.03/1.15 200m/20m 3m/2m
Blue 1.50/1.45 2.12/2.11 2.29/1.90 9m/2m
UV 1.42/63m 2.11/2.09 2.34/2.29 2.61/2.47

So Blue --> Green looks favourite, no better than UV --> Green but
easier to see.

If TX is longer wavelength than RX then nothing much, if TX is
considerably shorter than RX then weak. Best seems when TX is a little
shorter than RX as predicted by Martin Brown.

So five Green receivers gives me my 10V. Five Blue transmitters may
work with a gap, may need focussing, could use more powerful types.

Cheers

Good stuff. Thanks.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Monday, November 11, 2019 at 7:48:37 AM UTC-5, Clive Arthur wrote:

I did some crude testing with Red, Green, Blue and UV LEDs.

All 1210 SMD 'high brightness' types from the same supplier.

One of each in series at their rated 20mA, then holding another of each
against each in turn, no air gap, switching in 1M as a load.

First thing to notice is how much brighter the green appears to be, yes
I know that's where the eye is most sensitive, but it does stand out
more than I expected. The red and blue appear about the same brightness
as each other, the UV emits a little visible violet.

Volts OC/Volts 1M load (OC is DVM impedance)

Receive -> Red Green Blue UV
Tx
Red 1.53/1.50 3m/0 0/0 0/0
Green 1.59/1.58 2.03/1.15 200m/20m 3m/2m
Blue 1.50/1.45 2.12/2.11 2.29/1.90 9m/2m
UV 1.42/63m 2.11/2.09 2.34/2.29 2.61/2.47

So Blue --> Green looks favourite, no better than UV --> Green but
easier to see.

If TX is longer wavelength than RX then nothing much, if TX is
considerably shorter than RX then weak. Best seems when TX is a little
shorter than RX as predicted by Martin Brown.

So five Green receivers gives me my 10V. Five Blue transmitters may
work with a gap, may need focussing, could use more powerful types.

Cheers
--
Clive

Idea #1 - right-angle SMD LED array
[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

Idea #2 - A search for "multi-chip series green LED" gets lots of
results, e.g.

Power LEDs made with series die--
https://www.cree.com/led-components/products/xlamp-leds-arrays/xlamp-mc-e

3-in-series, custom, to your spec, for $4.50 per LED, 100 min.
https://lamptech.com/led/multi-chip-leds/build-your-own/

Idea #3 - If you've got lots of time, a simple 2-transistor relaxation
boost converter can boost 2V to 10V, allowing you to use just one LED
Tx-Rx pair instead of five.

Cheers,
James Arthur

 

[John Larkin]

On Mon, 11 Nov 2019 07:48:17 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Monday, November 11, 2019 at 7:48:37 AM UTC-5, Clive Arthur wrote:
I did some crude testing with Red, Green, Blue and UV LEDs.

All 1210 SMD 'high brightness' types from the same supplier.

One of each in series at their rated 20mA, then holding another of each
against each in turn, no air gap, switching in 1M as a load.

First thing to notice is how much brighter the green appears to be, yes
I know that's where the eye is most sensitive, but it does stand out
more than I expected. The red and blue appear about the same brightness
as each other, the UV emits a little visible violet.

Volts OC/Volts 1M load (OC is DVM impedance)

Receive -> Red Green Blue UV
Tx
Red 1.53/1.50 3m/0 0/0 0/0
Green 1.59/1.58 2.03/1.15 200m/20m 3m/2m
Blue 1.50/1.45 2.12/2.11 2.29/1.90 9m/2m
UV 1.42/63m 2.11/2.09 2.34/2.29 2.61/2.47

So Blue --> Green looks favourite, no better than UV --> Green but
easier to see.

If TX is longer wavelength than RX then nothing much, if TX is
considerably shorter than RX then weak. Best seems when TX is a little
shorter than RX as predicted by Martin Brown.

So five Green receivers gives me my 10V. Five Blue transmitters may
work with a gap, may need focussing, could use more powerful types.

Cheers
--
Clive

Idea #1 - right-angle SMD LED array
[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

Idea #2 - A search for "multi-chip series green LED" gets lots of
results, e.g.

Power LEDs made with series die--
https://www.cree.com/led-components/products/xlamp-leds-arrays/xlamp-mc-e

3-in-series, custom, to your spec, for $4.50 per LED, 100 min.
https://lamptech.com/led/multi-chip-leds/build-your-own/

Idea #3 - If you've got lots of time, a simple 2-transistor relaxation
boost converter can boost 2V to 10V, allowing you to use just one LED
Tx-Rx pair instead of five.

Cheers,
James Arthur

I suppose one could square-wave modulate the transmitter LEDs and
somehowmumblemumble use the AC on the receive side. That would give a
bit more peak voltage at the receiver, for a given average transmit
drive.



--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

[Clive Arthur]

On 11/11/2019 15:48, dagmargoodboat@yahoo.com wrote:

<snipped>

Idea #2 - A search for "multi-chip series green LED" gets lots of
results, e.g.

Power LEDs made with series die--
https://www.cree.com/led-components/products/xlamp-leds-arrays/xlamp-mc-e

Only white or RGB as far as I can see?

Cheers
--
Clive

 

[Bill Sloman]

On Tuesday, November 12, 2019 at 5:18:13 AM UTC+11, John Larkin wrote:

On Mon, 11 Nov 2019 07:48:17 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Monday, November 11, 2019 at 7:48:37 AM UTC-5, Clive Arthur wrote:
I did some crude testing with Red, Green, Blue and UV LEDs.

All 1210 SMD 'high brightness' types from the same supplier.

One of each in series at their rated 20mA, then holding another of each
against each in turn, no air gap, switching in 1M as a load.

First thing to notice is how much brighter the green appears to be, yes
I know that's where the eye is most sensitive, but it does stand out
more than I expected. The red and blue appear about the same brightness
as each other, the UV emits a little visible violet.

Volts OC/Volts 1M load (OC is DVM impedance)

Receive -> Red Green Blue UV
Tx
Red 1.53/1.50 3m/0 0/0 0/0
Green 1.59/1.58 2.03/1.15 200m/20m 3m/2m
Blue 1.50/1.45 2.12/2.11 2.29/1.90 9m/2m
UV 1.42/63m 2.11/2.09 2.34/2.29 2.61/2.47

So Blue --> Green looks favourite, no better than UV --> Green but
easier to see.

If TX is longer wavelength than RX then nothing much, if TX is
considerably shorter than RX then weak. Best seems when TX is a little
shorter than RX as predicted by Martin Brown.

So five Green receivers gives me my 10V. Five Blue transmitters may
work with a gap, may need focussing, could use more powerful types.

Cheers
--
Clive

Idea #1 - right-angle SMD LED array
[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

Idea #2 - A search for "multi-chip series green LED" gets lots of
results, e.g.

Power LEDs made with series die--
https://www.cree.com/led-components/products/xlamp-leds-arrays/xlamp-mc-e

3-in-series, custom, to your spec, for $4.50 per LED, 100 min.
https://lamptech.com/led/multi-chip-leds/build-your-own/

Idea #3 - If you've got lots of time, a simple 2-transistor relaxation
boost converter can boost 2V to 10V, allowing you to use just one LED
Tx-Rx pair instead of five.

I suppose one could square-wave modulate the transmitter LEDs and
somehowmumblemumble use the AC on the receive side. That would give a
bit more peak voltage at the receiver, for a given average transmit
drive.

The modulated current seems to be low, so you'd need a lot of primary inductance to generate voltage being asked for.

Not an easy transformer to find or get wound.

--
Bill Sloman, Sydney

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

On Monday, November 11, 2019 at 1:18:13 PM UTC-5, John Larkin wrote:

On Mon, 11 Nov 2019 07:48:17 -0800 (PST), dagmargoodboat@yahoo.com
wrote:

On Monday, November 11, 2019 at 7:48:37 AM UTC-5, Clive Arthur wrote:
I did some crude testing with Red, Green, Blue and UV LEDs.

All 1210 SMD 'high brightness' types from the same supplier.

One of each in series at their rated 20mA, then holding another of each
against each in turn, no air gap, switching in 1M as a load.

First thing to notice is how much brighter the green appears to be, yes
I know that's where the eye is most sensitive, but it does stand out
more than I expected. The red and blue appear about the same brightness
as each other, the UV emits a little visible violet.

Volts OC/Volts 1M load (OC is DVM impedance)

Receive -> Red Green Blue UV
Tx
Red 1.53/1.50 3m/0 0/0 0/0
Green 1.59/1.58 2.03/1.15 200m/20m 3m/2m
Blue 1.50/1.45 2.12/2.11 2.29/1.90 9m/2m
UV 1.42/63m 2.11/2.09 2.34/2.29 2.61/2.47

So Blue --> Green looks favourite, no better than UV --> Green but
easier to see.

If TX is longer wavelength than RX then nothing much, if TX is
considerably shorter than RX then weak. Best seems when TX is a little
shorter than RX as predicted by Martin Brown.

So five Green receivers gives me my 10V. Five Blue transmitters may
work with a gap, may need focussing, could use more powerful types.

Cheers
--
Clive

Idea #1 - right-angle SMD LED array
[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

[ ] [ ]
| )~~> ( |
[ ] [ ]

Idea #2 - A search for "multi-chip series green LED" gets lots of
results, e.g.

Power LEDs made with series die--
https://www.cree.com/led-components/products/xlamp-leds-arrays/xlamp-mc-e

3-in-series, custom, to your spec, for $4.50 per LED, 100 min.
https://lamptech.com/led/multi-chip-leds/build-your-own/

Idea #3 - If you've got lots of time, a simple 2-transistor relaxation
boost converter can boost 2V to 10V, allowing you to use just one LED
Tx-Rx pair instead of five.

Cheers,
James Arthur

There's an old circuit out there that uses an LED in PV mode to
collect power, to blink that same LED. Rather than that, Clive
could charge a cap up to a threshold, which fires a switch, that
charges an inductor. When the switch opens, the inductor flies
back.

It's almost easier to draw than describe, but I haven't the time
to ASCII it just now. Too busy.

I suppose one could square-wave modulate the transmitter LEDs and
somehowmumblemumble use the AC on the receive side. That would give a
bit more peak voltage at the receiver, for a given average transmit
drive.

Make a photovoltaic C-W! <grins>

Cheers,
James Arthur

 

On Mon, 11 Nov 2019 18:26:29 +0000, Clive Arthur
<cliveta@nowaytoday.co.uk> wrote:

On 11/11/2019 15:48, dagmargoodboat@yahoo.com wrote:

snipped

Idea #2 - A search for "multi-chip series green LED" gets lots of
results, e.g.

Power LEDs made with series die--
https://www.cree.com/led-components/products/xlamp-leds-arrays/xlamp-mc-e


Only white or RGB as far as I can see?

Cheers

Digikey has 12 and 24 volt blue LEDs

https://www.digikey.com/products/en/optoelectronics/led-lighting-color/125?FV=-8%7C125%2C37%7C320441%2C37%7C320579&quantity=0&ColumnSort=-319&page=1&pageSize=25

Look for "lighting" LEDs.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Monday, November 11, 2019 at 1:26:35 PM UTC-5, Clive Arthur wrote:

On 11/11/2019 15:48, dagmargoodboat@yahoo.com wrote:

snipped

Idea #2 - A search for "multi-chip series green LED" gets lots of
results, e.g.

Power LEDs made with series die--
https://www.cree.com/led-components/products/xlamp-leds-arrays/xlamp-mc-e


Only white or RGB as far as I can see?

Cheers
--
Clive

Rats, you're right. I like Cree, but their website and datasheets
are awful.

White-to-white wouldn't be ideally efficient, but white dual- and
triple-die (6v & 9v) white LEDs are very common.

And Marktech will make whatever you want.

Cheers,
James Arthur

 

[Clive Arthur]

On 12/11/2019 03:44, jlarkin@highlandsniptechnology.com wrote:

On Mon, 11 Nov 2019 18:26:29 +0000, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

On 11/11/2019 15:48, dagmargoodboat@yahoo.com wrote:

snipped

Idea #2 - A search for "multi-chip series green LED" gets lots of
results, e.g.

Power LEDs made with series die--
https://www.cree.com/led-components/products/xlamp-leds-arrays/xlamp-mc-e


Only white or RGB as far as I can see?

Cheers

Digikey has 12 and 24 volt blue LEDs

https://www.digikey.com/products/en/optoelectronics/led-lighting-color/125?FV=-8%7C125%2C37%7C320441%2C37%7C320579&quantity=0&ColumnSort=-319&page=1&pageSize=25

Look for "lighting" LEDs.

I looked at one of these and it's Parallel LEDs with a driver of some
sort as far as I can tell.

Cheers
--
Clive

 

[Martin Brown]

On 11/11/2019 15:22, jlarkin@highlandsniptechnology.com wrote:

On Mon, 11 Nov 2019 12:48:25 +0000, Clive Arthur
cliveta@nowaytoday.co.uk> wrote:

I did some crude testing with Red, Green, Blue and UV LEDs.

All 1210 SMD 'high brightness' types from the same supplier.

One of each in series at their rated 20mA, then holding another of each
against each in turn, no air gap, switching in 1M as a load.

First thing to notice is how much brighter the green appears to be, yes
I know that's where the eye is most sensitive, but it does stand out
more than I expected. The red and blue appear about the same brightness
as each other, the UV emits a little visible violet.

I'm using one family of LEDs where at equal currents, green is dim,
orange is nice, and blue is blinding. Had to change some resistors.

It is worth seeking out the LEDs with the highest lumen output and
smallest beam divergence that you can for this sort of game.

The QE of some of the highly optimised blue LEDs has benefitted
enormously from the white LED trade. The die surface luminosity is now
slightly higher than the surface of the sun at that wavelength.

Volts OC/Volts 1M load (OC is DVM impedance)

Receive -> Red Green Blue UV
Tx
Red 1.53/1.50 3m/0 0/0 0/0
Green 1.59/1.58 2.03/1.15 200m/20m 3m/2m
Blue 1.50/1.45 2.12/2.11 2.29/1.90 9m/2m
UV 1.42/63m 2.11/2.09 2.34/2.29 2.61/2.47

So Blue --> Green looks favourite, no better than UV --> Green but
easier to see.

If TX is longer wavelength than RX then nothing much, if TX is
considerably shorter than RX then weak. Best seems when TX is a little
shorter than RX as predicted by Martin Brown.

Cyan (505nm) driven by blue might get you slightly more voltage. Or if
the Cyan LED is up to it Green driven by Cyan - the overlap is tighter
for that pair but the output voltage marginally lower.

https://www.rapidonline.com/truopto-osbg5111p-5mm-cyan-led-30000mcd-55-2488

So five Green receivers gives me my 10V. Five Blue transmitters may
work with a gap, may need focussing, could use more powerful types.

Good stuff. Thanks.

The ones with 15 or 20 degree beam collimation make the most sense more
so if you can put them onto a clear Perspex rod light guide.

--
Regards,
Martin Brown