Prev: Auditing Cases Interactive Learning Approach (4thEd) - Beasley – Instructors Solutions Manual in pdf format is available for purchase at affordable prices. Contact me at alltestbanks11[at]gmail.com to buy it today.
Next: Back Alley
From: Tim Williams on 22 Mar 2010 11:07
"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

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


From: Tim Wescott on 22 Mar 2010 11:14
Jim Thompson wrote:
> On Mon, 22 Mar 2010 14:44:34 GMT, zekfrivo(a)zekfrivolous.com (GregS)
> wrote:
>
>> In article <a8e2d54d-cd89-4910-a6e5-2091bab0ce85(a)f13g2000pra.googlegroups.com>, MooseFET <kensmith(a)rahul.net> wrote:
>>> On Mar 21, 8:10=A0pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)My-
>>> Web-Site.com> 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)?
>>> I would expect a little under 0.5A per watt of light power hitting
>>> the diode.
>>>
>>> How big is the diode?
>>>
>>>> As usual, my customer has no clue. =A0My only concern, design wise, is
>>>> to build a micropower transconductance amplifier with sufficient
>>>> output drive to handle the maximum available photo current.
>>> Since you are working at low frequencies, you can run the diode at
>>> zero bias or some other value the circuit likes. This makes it a
>>> lot easier to do the amplifier design.
>> I would just MEASURE it with some diode. I just measured
>> 2 mv p-p into a scope 1M. Directly pointing at the light is
>> 14 mv p-p. Thats 2 micro volta to 14 micro volts.
>> I don't know what the diode is, but I have been using it
>> to measure light noise.
>>
>> greg
>
> Current. Transconductance. Not VOLTS.

Well, not "transconductance". "Photonic response", maybe.

Not to throw a wrench in your works, but with the right photodiode (i.e.
a smaller version of those photovoltaic diodes that you see on cheap
calculators) you could look at the diode's open-circuit voltage and more
or less automatically get the log of the ambient light for all but the
dimmest of illumination.

It would be temperature sensitive, but you could account for that by
measuring temperature in your circuit -- doing so with a diode that has
a fixed current going through it, and generating your PWM
ratiometrically, may just be the bee's knees.

It would also be subject to manufacturing variation, which may be more
of an issue.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: Oppie on 22 Mar 2010 11:14


"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?

From: John Larkin on 22 Mar 2010 11:45
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


.... for certain definitions of "PWM."


But yeah, PUTs were fun.

John


From: Tim Williams on 22 Mar 2010 11:50
"Oppie" <Oppie(a)saynotospam.com> wrote in message
news:yRLpn.28952$ao7.12608(a)newsfe21.iad...
>> http://webpages.charter.net/dawill/Images/Photodiode_PWM.gif
>
> Geez, I haven't futzed with PUTs in ages. Does anybody still make them?

PUTs aren't that hard to find. Maybe you're thinking of UJTs?
http://www.mouser.com/ProductDetail/ON-Semiconductor/2N6027G/?qs=sGAEpiMZZMtK7gk71q29LtJYaNkyBux0URy1Y7q4hnw%3d
Although I'll admit none of them are actually *in stock* right now.

Anyway, if they're on the expensive side ($0.25 in singles?), you can
Jeorgify your own from a 2N3904 and 2N3906 ($0.06/ea in singles)... the
equivalent circuit is as indicated (i.e., like an SCR, but take the second
junction).

Tim

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


First  |  Prev  |  Next  |  Last
Pages: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Prev: Auditing Cases Interactive Learning Approach (4thEd) - Beasley – Instructors Solutions Manual in pdf format is available for purchase at affordable prices. Contact me at alltestbanks11[at]gmail.com to buy it today.
Next: Back Alley