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From: Wimpie on 22 Mar 2010 12:24
On 22 mar, 15:31, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My-Web-
Site.com> wrote:
> On Mon, 22 Mar 2010 08:01:35 -0400, Phil Hobbs
>
>
>
> <pcdhSpamMeSensel...(a)electrooptical.net> wrote:
> >On 3/21/2010 11:10 PM, Jim Thompson wrote:
> >> What current would one expect to see from a photodiode exposed to
> >> typical bright room light (used to control a backlight proportional to
> >> room light)?
>
> >> As usual, my customer has no clue.  My only concern, design wise, is
> >> to build a micropower transconductance amplifier with sufficient
> >> output drive to handle the maximum available photo current.
>
> >>                                          ...Jim Thompson
>
> >Those guys are all nuts.
>
> >For backlight control, you can use one of the ambient light sensors such
> >as the Intersil ISL29000 or TAOS TSL2560, for instance.  They look after
> >all of that nonsense, and produce an analogue or digital output
> >proportional to just the perceived brightness (i.e. luminous intensity),
> >without being fooled by all the IR from incandescents, for instance.
>
> >Full zenith sunlight is about 800W/m**2, so figuring 0.3 A/W average
> >responsivity, a typical 2.3 mm square photodiode such as a BPW34 will
> >never produce more than ~1.3 mA without optical concentration of some
> >sort.  Indoors it's a factor of 10**3 to 10**4 dimmer than that, so
> >you're looking at a few microamps in bright room lights.
>
> >Cheers
>
> >Phil Hobbs
>
> My task is to produce a PWM output proportional to a photodiode
> current.
>
> I guess I need to find a typical one and measure it myself.
>
>                                         ...Jim Thompson
> --
> | James E.Thompson, CTO                            |    mens     |
> | Analog Innovations, Inc.                         |     et      |
> | Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
> | Phoenix, Arizona  85048    Skype: Contacts Only  |             |
> | Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
> | E-mail Icon athttp://www.analog-innovations.com|    1962     |
>
>       The only thing bipartisan in this country is hypocrisy

Hello Jim,

For the experiments, take one (Photo diode/transistor, LDR, ambient
light sensor) with a wide viewing angle (somewhat over 90 degrees).
Measure the response also for a filament lamp, fluorescent tube/lamp,
white LED lamp and sun under low elevation angle. You may also
experiment with white plastic as a diffuser. It reduces sensitivity,
but increases viewing angle when using narrow viewing angle photo
diodes/transistors.

Compare the values with you own eye perception.

Good luck with the experiments and best regards,


Wim
PA3DJS
www.tetech.nl
without abc, PM will reach me
From: Jim Thompson on 22 Mar 2010 12:42
On Mon, 22 Mar 2010 10:07:56 -0500, "Tim Williams"
<tmoranwms(a)charter.net> wrote:

>"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in
>message news:hoveq5paaq3k2b28unqe67u0ojd7cdom8n(a)4ax.com...
>> My task is to produce a PWM output proportional to a photodiode
>> current.
>>
>> I guess I need to find a typical one and measure it myself.
>
>Well, you didn't specify what kind of proportionality, so I guess I win
>firsties.
>http://webpages.charter.net/dawill/Images/Photodiode_PWM.gif
>
>Tim

Except that's current-to-frequency :-)

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

The only thing bipartisan in this country is hypocrisy
From: Grant on 22 Mar 2010 12:44
On Mon, 22 Mar 2010 11:14:44 -0400, "Oppie" <Oppie(a)saynotospam.com> wrote:

>
>
>"Tim Williams" <tmoranwms(a)charter.net> wrote in message
>news:ho814m$3st$1(a)news.eternal-september.org...
>
>> http://webpages.charter.net/dawill/Images/Photodiode_PWM.gif
>>
>> Tim
>>
>Geez, I haven't futzed with PUTs in ages. Does anybody still make them?

Showing my age? 2N6027 Yes, they're available ;)

On Semi.

Grant.
From: Tim Williams on 22 Mar 2010 13:57
"Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)My-Web-Site.com> wrote in
message news:fe7fq5lbivoa4o7gn67gho2mt8pj2d4dh8(a)4ax.com...
>>http://webpages.charter.net/dawill/Images/Photodiode_PWM.gif
>
> Except that's current-to-frequency :-)

On-time is constant, so it's PWM. You didn't say if frequency had to be
constant. No specs, remember? ;-)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


From: John Larkin on 22 Mar 2010 14:53
On Mon, 22 Mar 2010 09:58:43 -0400, Phil Hobbs
<pcdhSpamMeSenseless(a)electrooptical.net> wrote:

>On 3/22/2010 9:52 AM, John Larkin wrote:
>> On Mon, 22 Mar 2010 08:01:35 -0400, Phil Hobbs
>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote:
>>
>>> On 3/21/2010 11:10 PM, Jim Thompson wrote:
>>>> What current would one expect to see from a photodiode exposed to
>>>> typical bright room light (used to control a backlight proportional to
>>>> room light)?
>>>>
>>>> As usual, my customer has no clue. My only concern, design wise, is
>>>> to build a micropower transconductance amplifier with sufficient
>>>> output drive to handle the maximum available photo current.
>>>>
>>>> ...Jim Thompson
>>>
>>> Those guys are all nuts.
>>
>> Then I'm sure glad I didn't make any suggestions.
>>
>> John
>>
>
>Nah, it's just my rhetorical way of trying to get people to do a bit of
>calculation (or even experiment) before giving advice. I know, I know,
>I'm on Usenet, but we must live in hope. ;)
>
>Cheers
>
>Phil Hobbs

I recall a recent lawsuit (maybe the Hynix/TI thing) over a design for
an ambient light sensor chip that used semi processing to get
human-similar wavelength response.

Scads of people offer ambient light sensor chips.

John

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