Cell phone giving off NIR bursts of light?

G

George Herold

Guest
So I'm building this photodiode/ noise electronics
I'm just bringing up the system and testing things out.
And I've got this really weak light signal I can't trace
down. Every ~114 ms there is square wave burst...
eight steps ~15 us period. I can block it by waving
pieces of card board around... anyway long story short.
My cell phone in the off state is sending out these bursts
and they were bouncing off the ceiling and getting into my detector.

I'd post a pick but there's a little gain peaking in my
PD TIA that I have to clean up first. :^)

Hey, maybe I can use this for testing... I wonder how sharp the
edge is?

George H.
 
On 2020-03-13 14:22, George Herold wrote:
So I'm building this photodiode/ noise electronics
I'm just bringing up the system and testing things out.
And I've got this really weak light signal I can't trace
down. Every ~114 ms there is square wave burst...
eight steps ~15 us period. I can block it by waving
pieces of card board around... anyway long story short.
My cell phone in the off state is sending out these bursts
and they were bouncing off the ceiling and getting into my detector.

I'd post a pick but there's a little gain peaking in my
PD TIA that I have to clean up first. :^)

Hey, maybe I can use this for testing... I wonder how sharp the
edge is?

George H.
Click to expand...

IRDA, perhaps.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On 2020-03-13 15:15, keith wright wrote:
On Friday, 13 March 2020 11:32:27 UTC-7, Phil Hobbs wrote: ....

IRDA, perhaps.
....

More likely it is the proximity sensor. If so it would probably come
from the top front-surface of the phone near the speaker.

On the iPhone we use IR modulated at about 100-300kHz as a
short-range sensor.
Click to expand...

That's probably right. I've never used one myself, but I know they exist.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com
 
On Friday, 13 March 2020 11:32:27 UTC-7, Phil Hobbs wrote:
....
IRDA, perhaps.
....
Click to expand...

More likely it is the proximity sensor. If so it would probably come from the top front-surface of the phone near the speaker.

On the iPhone we use IR modulated at about 100-300kHz as a short-range sensor.

kw
 
George Herold <ggherold@gmail.com> writes:

So I'm building this photodiode/ noise electronics
I'm just bringing up the system and testing things out.
And I've got this really weak light signal I can't trace
down. Every ~114 ms there is square wave burst...
eight steps ~15 us period. I can block it by waving
pieces of card board around... anyway long story short.
My cell phone in the off state is sending out these bursts
and they were bouncing off the ceiling and getting into my detector.
Click to expand...

Probably close to the speaker - many phones use IR proximity sensor to
detect they're close to you to disable 'buttons' during a call.

--
mikko
 
On Friday, March 13, 2020 at 3:18:43 PM UTC-4, Mikko OH2HVJ wrote:
George Herold <ggherold@gmail.com> writes:

So I'm building this photodiode/ noise electronics
I'm just bringing up the system and testing things out.
And I've got this really weak light signal I can't trace
down. Every ~114 ms there is square wave burst...
eight steps ~15 us period. I can block it by waving
pieces of card board around... anyway long story short.
My cell phone in the off state is sending out these bursts
and they were bouncing off the ceiling and getting into my detector.

Probably close to the speaker - many phones use IR proximity sensor to
detect they're close to you to disable 'buttons' during a call.

--
mikko
Click to expand...

Yeah thanks. It was actually useful... maybe there is some app
that lets me control the blink. I'll have to try and measure the
edge. (Right now a 1 meg FB resistor, ~1 us, slow)

So what's the detector? There's a front camera too, is that it?

I'll have to search some.

Having a set length/number pulse train is a little like a lockin...
but further encoded.

George H.
 
On Friday, March 13, 2020 at 3:16:00 PM UTC-4, keith wright wrote:
On Friday, 13 March 2020 11:32:27 UTC-7, Phil Hobbs wrote:
...

IRDA, perhaps.
...

More likely it is the proximity sensor. If so it would probably come from the top front-surface of the phone near the speaker.

On the iPhone we use IR modulated at about 100-300kHz as a short-range sensor.

kw
Click to expand...

Thanks Keith, yeah front surface near the speaker.
I did use it to tweak the PD response.
But it was a pain to ID.

George H.
 
On Friday, March 13, 2020 at 2:25:37 PM UTC-7, George Herold wrote:

> So what's the detector? There's a front camera too, is that it?

Perhaps it's the 'ear detector' that determines if your phone is held against your head
and in no need of backlight. Irritating little mechanism, when I pull the
phone away in order to hit the hangup 'button', it's always dark.
 
On Friday, 13 March 2020 16:14:17 UTC-7, whit3rd wrote:
On Friday, March 13, 2020 at 2:25:37 PM UTC-7, George Herold wrote:

So what's the detector? There's a front camera too, is that it?

Perhaps it's the 'ear detector' that determines if your phone is held against your head
and in no need of backlight. Irritating little mechanism, when I pull the
phone away in order to hit the hangup 'button', it's always dark.
Click to expand...

The proximity detector is usually only active during a call though.

In George's phone it seems to be active when the phone is idle - maybe something to wake up the phone when the user reaches for the phone.

Some new phones have a more sophisticated scheme using time-of-flight measurement with ranges of a couple of feet and resolution of a few mm.

For example: https://ams.com/-/ams-introduces-world-s-smallest-1d-time-of-flight-sen-sor-for-accurate-proximity-sensing-and-distance-measurement-in-smartphones

kw
 
On Friday, March 13, 2020 at 7:55:48 PM UTC-4, keith wright wrote:
On Friday, 13 March 2020 14:25:37 UTC-7, George Herold wrote:
...
Yeah thanks. It was actually useful... maybe there is some app
that lets me control the blink. I'll have to try and measure the
edge. (Right now a 1 meg FB resistor, ~1 us, slow)

So what's the detector? There's a front camera too, is that it?
...

The detector will be a silicon photodiode - the IR beam will probably be modulated at 100kHz or (it is in iPhones). The camera is too slow.

kw
Click to expand...

This is an LG phone from years ago.
Once every ~114 ms an 8 bit square wave, ~15 us period.

But good to know if you are ever in a dark room testing
some photo sensor.

GH
 
On Friday, 13 March 2020 14:25:37 UTC-7, George Herold wrote:
....
Yeah thanks. It was actually useful... maybe there is some app
that lets me control the blink. I'll have to try and measure the
edge. (Right now a 1 meg FB resistor, ~1 us, slow)

So what's the detector? There's a front camera too, is that it?
....
Click to expand...

The detector will be a silicon photodiode - the IR beam will probably be modulated at 100kHz or (it is in iPhones). The camera is too slow.

kw
 
On 14/3/20 12:10 pm, George Herold wrote:
On Friday, March 13, 2020 at 8:26:03 PM UTC-4, keith wright wrote:
On Friday, 13 March 2020 16:14:17 UTC-7, whit3rd wrote:
On Friday, March 13, 2020 at 2:25:37 PM UTC-7, George Herold wrote:

So what's the detector? There's a front camera too, is that it?

Perhaps it's the 'ear detector' that determines if your phone is held against your head
and in no need of backlight. Irritating little mechanism, when I pull the
phone away in order to hit the hangup 'button', it's always dark.

The proximity detector is usually only active during a call though.

In George's phone it seems to be active when the phone is idle - maybe something to wake up the phone when the user reaches for the phone.

Some new phones have a more sophisticated scheme using time-of-flight measurement with ranges of a couple of feet and resolution of a few mm.

For example: https://ams.com/-/ams-introduces-world-s-smallest-1d-time-of-flight-sen-sor-for-accurate-proximity-sensing-and-distance-measurement-in-smartphones

kw

OK after some f-ing around trying to turn stuff on and off, I found that
the light is also active when making a phone call.
So here's my story.
Some marketing guy asked, "Can we make the battery life of this cheaper
phone less?" And the engineer said, "We could leave the proximity
LED on when the phone is off." and the marketing guy said "Perfect."
Click to expand...

My Motorola phone shows the lockscreen dimly (battery, time/date,
notifications, etc) whenever you put your hand near it. That's clearly a
prox sensor, probably IR.

CH
 
On Friday, March 13, 2020 at 8:26:03 PM UTC-4, keith wright wrote:
On Friday, 13 March 2020 16:14:17 UTC-7, whit3rd wrote:
On Friday, March 13, 2020 at 2:25:37 PM UTC-7, George Herold wrote:

So what's the detector? There's a front camera too, is that it?

Perhaps it's the 'ear detector' that determines if your phone is held against your head
and in no need of backlight. Irritating little mechanism, when I pull the
phone away in order to hit the hangup 'button', it's always dark.

The proximity detector is usually only active during a call though.

In George's phone it seems to be active when the phone is idle - maybe something to wake up the phone when the user reaches for the phone.

Some new phones have a more sophisticated scheme using time-of-flight measurement with ranges of a couple of feet and resolution of a few mm.

For example: https://ams.com/-/ams-introduces-world-s-smallest-1d-time-of-flight-sen-sor-for-accurate-proximity-sensing-and-distance-measurement-in-smartphones

kw
Click to expand...

OK after some f-ing around trying to turn stuff on and off, I found that
the light is also active when making a phone call.
So here's my story.
Some marketing guy asked, "Can we make the battery life of this cheaper
phone less?" And the engineer said, "We could leave the proximity
LED on when the phone is off." and the marketing guy said "Perfect."

George H.
 
On Sat, 14 Mar 2020 12:18:20 +1100, Clifford Heath
<no.spam@please.net> wrote:

On 14/3/20 12:10 pm, George Herold wrote:
On Friday, March 13, 2020 at 8:26:03 PM UTC-4, keith wright wrote:
On Friday, 13 March 2020 16:14:17 UTC-7, whit3rd wrote:
On Friday, March 13, 2020 at 2:25:37 PM UTC-7, George Herold wrote:

So what's the detector? There's a front camera too, is that it?

Perhaps it's the 'ear detector' that determines if your phone is held against your head
and in no need of backlight. Irritating little mechanism, when I pull the
phone away in order to hit the hangup 'button', it's always dark.

The proximity detector is usually only active during a call though.

In George's phone it seems to be active when the phone is idle - maybe something to wake up the phone when the user reaches for the phone.

Some new phones have a more sophisticated scheme using time-of-flight measurement with ranges of a couple of feet and resolution of a few mm.

For example: https://ams.com/-/ams-introduces-world-s-smallest-1d-time-of-flight-sen-sor-for-accurate-proximity-sensing-and-distance-measurement-in-smartphones

kw

OK after some f-ing around trying to turn stuff on and off, I found that
the light is also active when making a phone call.
So here's my story.
Some marketing guy asked, "Can we make the battery life of this cheaper
phone less?" And the engineer said, "We could leave the proximity
LED on when the phone is off." and the marketing guy said "Perfect."

My Motorola phone shows the lockscreen dimly (battery, time/date,
notifications, etc) whenever you put your hand near it. That's clearly a
prox sensor, probably IR.

CH
Click to expand...

That and more are all part of Motorola "Moto Actions":
<https://motorola-global-portal.custhelp.com/app/answers/indevice_detail/a_id/112154/p/30,6720,9833>
To the best of my limited knowledge, these features are based on IR
emitters/detectors and are always on (unless you deactivate all the
Moto Action features). That became a problem for Motorola, so they
removed Moto Actions. Someone wrote the Gravity Gestures app that
replaces most of the gestures:
<https://play.google.com/store/apps/details?id=com.tinoooapp.gravitygestures>

Reminder: You can "see" Near IR emissions with most digital cameras.
Try the camera with an IR remote control first to make sure the camera
works in IR.


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
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