Super sensitive light sensor...

sonnic...@gmail.com · Jul 31, 2023

I am trying to detect light in a range from complete darkness to a tiny bit of light.
Imagine my test set - a shoe box with a mobile phone, that way I can make it ring and get light. The room light is way more than present in the real situation. I could also use a water pipe and place a phone in the middle
The light I want to detect is not natural, it will be LED and other light meant for humans (no IR or so).
Also the space it will be used is very tiny. I cannot change the light provided in case some would suggest that.

The easy solution would be and LDR or photo transistor, some resistors and a comparator or ADC

I have tried with LDR\'s and found only a few that gives enough change on \"a tiny change in light\", however that work on my desk light on/off, but that is not the real case.
I also found LDRs to react to light fast, but returning to dark is slow for some of them. This is ok, but I still found them too different to be reliable. I tried 5 of the same type and got 5 very different results. Once again, solvable in SW, ADC read min and max and react accordingly. But still.....

I have tried one photo transistor which reads 860nm (~red), but it does not give any reading except 1-10mV (5V in series with 4K7), and a setup with an op-amp for amplifying it works with room light

Now, my transistor is at 860nm or red, and I am looking at present light, so I found another one that works around 550nm, which simulates the human eye:
Datasheet: https://www.teval.ee/shop/product/pt-ic-ac-5-pn-520-phototransistor-5mm-p-max-520nm-lens-transparent-front-flat-368844/attachment/350084/PT-IC-AC-5-PE-550.pdf
I am considering ordering these for testing.

What can the community here suggest?
I need a rest and new thoughts now

Ricky · Jul 31, 2023

On Friday, July 21, 2023 at 1:25:47â¯PM UTC-4, sonnic...@gmail.com wrote:

I am trying to detect light in a range from complete darkness to a tiny bit of light.
Imagine my test set - a shoe box with a mobile phone, that way I can make it ring and get light. The room light is way more than present in the real situation. I could also use a water pipe and place a phone in the middle
The light I want to detect is not natural, it will be LED and other light meant for humans (no IR or so).
Also the space it will be used is very tiny. I cannot change the light provided in case some would suggest that.

The easy solution would be and LDR or photo transistor, some resistors and a comparator or ADC

I have tried with LDR\'s and found only a few that gives enough change on \"a tiny change in light\", however that work on my desk light on/off, but that is not the real case.
I also found LDRs to react to light fast, but returning to dark is slow for some of them. This is ok, but I still found them too different to be reliable. I tried 5 of the same type and got 5 very different results. Once again, solvable in SW, ADC read min and max and react accordingly. But still.....

I have tried one photo transistor which reads 860nm (~red), but it does not give any reading except 1-10mV (5V in series with 4K7), and a setup with an op-amp for amplifying it works with room light

Now, my transistor is at 860nm or red, and I am looking at present light, so I found another one that works around 550nm, which simulates the human eye:
Datasheet: https://www.teval.ee/shop/product/pt-ic-ac-5-pn-520-phototransistor-5mm-p-max-520nm-lens-transparent-front-flat-368844/attachment/350084/PT-IC-AC-5-PE-550.pdf
I am considering ordering these for testing.

What can the community here suggest?
I need a rest and new thoughts now

Photomultiplier tubes are very sensitive. They can count individual photons.

Or, you can drop the value of the resistor in your photo transistor circuit to a smaller value. What voltage level do you need?

--

Rick C.

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

sonnic...@gmail.com · Jul 31, 2023

On Friday, 21 July 2023 at 20:32:03 UTC+3, Ricky wrote:

On Friday, July 21, 2023 at 1:25:47â¯PM UTC-4, sonnic...@gmail.com wrote:
I am trying to detect light in a range from complete darkness to a tiny bit of light.
Imagine my test set - a shoe box with a mobile phone, that way I can make it ring and get light. The room light is way more than present in the real situation. I could also use a water pipe and place a phone in the middle
The light I want to detect is not natural, it will be LED and other light meant for humans (no IR or so).
Also the space it will be used is very tiny. I cannot change the light provided in case some would suggest that.

The easy solution would be and LDR or photo transistor, some resistors and a comparator or ADC

I have tried with LDR\'s and found only a few that gives enough change on \"a tiny change in light\", however that work on my desk light on/off, but that is not the real case.
I also found LDRs to react to light fast, but returning to dark is slow for some of them. This is ok, but I still found them too different to be reliable. I tried 5 of the same type and got 5 very different results. Once again, solvable in SW, ADC read min and max and react accordingly. But still....

I have tried one photo transistor which reads 860nm (~red), but it does not give any reading except 1-10mV (5V in series with 4K7), and a setup with an op-amp for amplifying it works with room light

Now, my transistor is at 860nm or red, and I am looking at present light, so I found another one that works around 550nm, which simulates the human eye:
Datasheet: https://www.teval.ee/shop/product/pt-ic-ac-5-pn-520-phototransistor-5mm-p-max-520nm-lens-transparent-front-flat-368844/attachment/350084/PT-IC-AC-5-PE-550.pdf
I am considering ordering these for testing.

What can the community here suggest?
I need a rest and new thoughts now
Photomultiplier tubes are very sensitive. They can count individual photons.

Or, you can drop the value of the resistor in your photo transistor circuit to a smaller value. What voltage level do you need?

The processing system runs on 5V. So getting something 1-4V would be useful, but the range is less important as long as I can get something reliable, 1-2V is fine, as long as I can process it down the line.
I have played around with resistors from 1K to 2M2 and different setups. My brain needs a break and good ideas

Ricky · Jul 31, 2023

On Friday, July 21, 2023 at 1:36:34â¯PM UTC-4, sonnic...@gmail.com wrote:

On Friday, 21 July 2023 at 20:32:03 UTC+3, Ricky wrote:
On Friday, July 21, 2023 at 1:25:47â¯PM UTC-4, sonnic...@gmail.com wrote:
I am trying to detect light in a range from complete darkness to a tiny bit of light.
Imagine my test set - a shoe box with a mobile phone, that way I can make it ring and get light. The room light is way more than present in the real situation. I could also use a water pipe and place a phone in the middle
The light I want to detect is not natural, it will be LED and other light meant for humans (no IR or so).
Also the space it will be used is very tiny. I cannot change the light provided in case some would suggest that.

The easy solution would be and LDR or photo transistor, some resistors and a comparator or ADC

I have tried with LDR\'s and found only a few that gives enough change on \"a tiny change in light\", however that work on my desk light on/off, but that is not the real case.
I also found LDRs to react to light fast, but returning to dark is slow for some of them. This is ok, but I still found them too different to be reliable. I tried 5 of the same type and got 5 very different results. Once again, solvable in SW, ADC read min and max and react accordingly. But still....

I have tried one photo transistor which reads 860nm (~red), but it does not give any reading except 1-10mV (5V in series with 4K7), and a setup with an op-amp for amplifying it works with room light

Now, my transistor is at 860nm or red, and I am looking at present light, so I found another one that works around 550nm, which simulates the human eye:
Datasheet: https://www.teval.ee/shop/product/pt-ic-ac-5-pn-520-phototransistor-5mm-p-max-520nm-lens-transparent-front-flat-368844/attachment/350084/PT-IC-AC-5-PE-550.pdf
I am considering ordering these for testing.

What can the community here suggest?
I need a rest and new thoughts now
Photomultiplier tubes are very sensitive. They can count individual photons.

Or, you can drop the value of the resistor in your photo transistor circuit to a smaller value. What voltage level do you need?
The processing system runs on 5V. So getting something 1-4V would be useful, but the range is less important as long as I can get something reliable, 1-2V is fine, as long as I can process it down the line.
I have played around with resistors from 1K to 2M2 and different setups. My brain needs a break and good ideas

Actually, I told you wrong. A large resistor will give more gain. What voltage level did you see with the 2.2 Meg resistor?

Oh, only change one thing at a time to be sure of what you are testing.

--

Rick C.

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

John Larkin · Jul 31, 2023

On Fri, 21 Jul 2023 10:25:41 -0700 (PDT), \"sonnic...@gmail.com\"
<sonnichjensen@gmail.com> wrote:

I am trying to detect light in a range from complete darkness to a tiny bit of light.
Imagine my test set - a shoe box with a mobile phone, that way I can make it ring and get light. The room light is way more than present in the real situation. I could also use a water pipe and place a phone in the middle
The light I want to detect is not natural, it will be LED and other light meant for humans (no IR or so).
Also the space it will be used is very tiny. I cannot change the light provided in case some would suggest that.

The easy solution would be and LDR or photo transistor, some resistors and a comparator or ADC

I have tried with LDR\'s and found only a few that gives enough change on \"a tiny change in light\", however that work on my desk light on/off, but that is not the real case.
I also found LDRs to react to light fast, but returning to dark is slow for some of them. This is ok, but I still found them too different to be reliable. I tried 5 of the same type and got 5 very different results. Once again, solvable in SW, ADC read min and max and react accordingly. But still....

I have tried one photo transistor which reads 860nm (~red), but it does not give any reading except 1-10mV (5V in series with 4K7), and a setup with an op-amp for amplifying it works with room light

Now, my transistor is at 860nm or red, and I am looking at present light, so I found another one that works around 550nm, which simulates the human eye:
Datasheet: https://www.teval.ee/shop/product/pt-ic-ac-5-pn-520-phototransistor-5mm-p-max-520nm-lens-transparent-front-flat-368844/attachment/350084/PT-IC-AC-5-PE-550.pdf
I am considering ordering these for testing.

What can the community here suggest?
I need a rest and new thoughts now

LDRs are terrible.

A large-area photodiode would make a lot of signal, preferably
back-biased current, not PV mode.

I have a bunch of First Sensor parts

https://www.gophotonics.com/products/photodiodes/first-sensor/56-642-501427

and I could send you a few.

Don Y · Jul 31, 2023

On 7/21/2023 10:25 AM, sonnic...@gmail.com wrote:

I am trying to detect light in a range from complete darkness to a tiny bit
of light.

It would be nice to know what \"tiny\" actually meant and how you
planned on detecting it. E.g., I can see the blue power LED on one
of my computers reflecting off the wall even though the lamp itself
is not directly visible.

Also, how quickly you want to detect that light source and how
persistent it is expected to be (latency and frequency).

The light I want to detect is not natural, it will be LED and other light
meant for humans (no IR or so).

Also the space it will be used is very tiny.

The easy solution would be and LDR or photo transistor, some resistors and a
comparator or ADC

That gives you a yes/no solution at the speed of the detector.
If you can afford to wait, you can integrate the detected light
source and get \"how much\" over \"some time\". Of course, this
assumes the source isn\'t infrequent and short-lived.

[We\'ve used this approach to detect color in lab assays... the
technician doesn\'t care if he waits a few seconds for a conclusive
reading...]

I also found LDRs to react to light fast, but returning to dark is slow for
some of them. This is ok, but I still found them too different to be
reliable. I tried 5 of the same type and got 5 very different results. Once
again, solvable in SW, ADC read min and max and react accordingly. But
still....

So, there are smarts available; you don\'t need a closed-form solution.
Does the environment change during deployment?

Anthony William Sloman · Jul 31, 2023

On Saturday, July 22, 2023 at 3:25:47â¯AM UTC+10, sonnic...@gmail.com wrote:

I am trying to detect light in a range from complete darkness to a tiny bit of light.
Imagine my test set - a shoe box with a mobile phone, that way I can make it ring and get light. The room light is way more than present in the real situation. I could also use a water pipe and place a phone in the middle
The light I want to detect is not natural, it will be LED and other light meant for humans (no IR or so).
Also the space it will be used is very tiny. I cannot change the light provided in case some would suggest that.

The easy solution would be and LDR or photo transistor, some resistors and a comparator or ADC

I have tried with LDR\'s and found only a few that gives enough change on \"a tiny change in light\", however that work on my desk light on/off, but that is not the real case.
I also found LDRs to react to light fast, but returning to dark is slow for some of them. This is ok, but I still found them too different to be reliable. I tried 5 of the same type and got 5 very different results. Once again, solvable in SW, ADC read min and max and react accordingly. But still.....

I have tried one photo transistor which reads 860nm (~red), but it does not give any reading except 1-10mV (5V in series with 4K7), and a setup with an op-amp for amplifying it works with room light

Now, my transistor is at 860nm or red, and I am looking at present light, so I found another one that works around 550nm, which simulates the human eye:
Datasheet: https://www.teval.ee/shop/product/pt-ic-ac-5-pn-520-phototransistor-5mm-p-max-520nm-lens-transparent-front-flat-368844/attachment/350084/PT-IC-AC-5-PE-550.pdf
I am considering ordering these for testing.

What can the community here suggest?
I need a rest and new thoughts now

https://en.wikipedia.org/wiki/Single-photon_avalanche_diode

is small and hard to beat for sensitivity, but they are noisy, and the electronics are trjcky, though they can be compact.

--
Bill Sloman, Sydney

amal banerjee · Jul 31, 2023

On Friday, July 21, 2023 at 10:55:47â¯PM UTC+5:30, sonnic...@gmail.com wrote:

I am trying to detect light in a range from complete darkness to a tiny bit of light.
Imagine my test set - a shoe box with a mobile phone, that way I can make it ring and get light. The room light is way more than present in the real situation. I could also use a water pipe and place a phone in the middle
The light I want to detect is not natural, it will be LED and other light meant for humans (no IR or so).
Also the space it will be used is very tiny. I cannot change the light provided in case some would suggest that.

The easy solution would be and LDR or photo transistor, some resistors and a comparator or ADC

I have tried with LDR\'s and found only a few that gives enough change on \"a tiny change in light\", however that work on my desk light on/off, but that is not the real case.
I also found LDRs to react to light fast, but returning to dark is slow for some of them. This is ok, but I still found them too different to be reliable. I tried 5 of the same type and got 5 very different results. Once again, solvable in SW, ADC read min and max and react accordingly. But still.....

I have tried one photo transistor which reads 860nm (~red), but it does not give any reading except 1-10mV (5V in series with 4K7), and a setup with an op-amp for amplifying it works with room light

Now, my transistor is at 860nm or red, and I am looking at present light, so I found another one that works around 550nm, which simulates the human eye:
Datasheet: https://www.teval.ee/shop/product/pt-ic-ac-5-pn-520-phototransistor-5mm-p-max-520nm-lens-transparent-front-flat-368844/attachment/350084/PT-IC-AC-5-PE-550.pdf
I am considering ordering these for testing.

What can the community here suggest?
I need a rest and new thoughts now

A reverse biased LED is the starting point. Phototransistors are not sensitive, nowhere close to a
photodiode. Please check out:
1. https://wiki.analog.com/university/courses/electronics/electronics-lab-led-sensor
2. https://www.electronicsforu.com/electronics-projects/led-light-sensor
3. https://www.circuits-diy.com/led-as-a-light-detector-circuit/
4. https://www.instructables.com/LEDs-as-light-sensors/

Hope that helps.

Anthony William Sloman · Jul 31, 2023

On Sunday, July 23, 2023 at 12:50:00â¯AM UTC+10, amal banerjee wrote:

On Friday, July 21, 2023 at 10:55:47â¯PM UTC+5:30, sonnic...@gmail..com wrote:
I am trying to detect light in a range from complete darkness to a tiny bit of light.
Imagine my test set - a shoe box with a mobile phone, that way I can make it ring and get light. The room light is way more than present in the real situation. I could also use a water pipe and place a phone in the middle
The light I want to detect is not natural, it will be LED and other light meant for humans (no IR or so).
Also the space it will be used is very tiny. I cannot change the light provided in case some would suggest that.

The easy solution would be and LDR or photo transistor, some resistors and a comparator or ADC

I have tried with LDR\'s and found only a few that gives enough change on \"a tiny change in light\", however that work on my desk light on/off, but that is not the real case.
I also found LDRs to react to light fast, but returning to dark is slow for some of them. This is ok, but I still found them too different to be reliable. I tried 5 of the same type and got 5 very different results. Once again, solvable in SW, ADC read min and max and react accordingly. But still....

I have tried one photo transistor which reads 860nm (~red), but it does not give any reading except 1-10mV (5V in series with 4K7), and a setup with an op-amp for amplifying it works with room light

Now, my transistor is at 860nm or red, and I am looking at present light, so I found another one that works around 550nm, which simulates the human eye:
Datasheet: https://www.teval.ee/shop/product/pt-ic-ac-5-pn-520-phototransistor-5mm-p-max-520nm-lens-transparent-front-flat-368844/attachment/350084/PT-IC-AC-5-PE-550.pdf
I am considering ordering these for testing.

What can the community here suggest?
I need a rest and new thoughts now
A reverse biased LED is the starting point. Phototransistors are not sensitive, nowhere close to a
photodiode. Please check out:

This is nuts. A phototransistor is effectively a photodiode plus a transistor in which the photodiode current serves as the base current drive for the transistor.

You get more amps per lumen than you do with a photodiode, so it is more sensitive than photodiode. It\'s not great for measuring low light levels because the collector base leakage current adds to the light signal.

1. https://wiki.analog.com/university/courses/electronics/electronics-lab-led-sensor
2. https://www.electronicsforu.com/electronics-projects/led-light-sensor
3. https://www.circuits-diy.com/led-as-a-light-detector-circuit/
4. https://www.instructables.com/LEDs-as-light-sensors/

Hope that helps.

It probably won\'t.

LEDs are famously photosensitive, but they are not designed or specified for the job.

It would be interesting to see a LED used as single photon avalanche diode..

https://www.farnell.com/datasheets/3698991.pdf

offers a red LED with 12V reverse voltage which is easy enough to set up. Compact package too.

--
Bill Sloman, Sydney

whit3rd · Jul 31, 2023

On Friday, July 21, 2023 at 10:25:47â¯AM UTC-7, sonnic...@gmail.com wrote:

I am trying to detect light in a range from complete darkness to a tiny bit of light.

What you\'d really want, then, is a logarithm-scale sensor of visible light?
Logarithm-of-current tricks with transistors can accomplish that.

Three or four differently-biased photodiodes, with different gains, and
a bit of logic to splice the ranges together might work, too.

The phototransistor sensitivity to red and IR is good, but not to blue or green...
some kind of filter is necessary to get insensitivity to IR, and a blue or
green LED might be better sensitivity than silicon for the full \'visible light\'
range; TEPT5700 is a Vishay diode-filter that mimics human-eye sensitivity.

Super sensitive light sensor...

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