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'[EE]: Phototransistors (*holding my head in shame*'
2003\07\08@083914 by Marc Nicholas

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This is probably a really, really dumb question...and probably a result of
my lack of formal electronics education ;-)

Why do three pin phototransistors exist? Is it purely for
aesthetics/standardized packaging reasons, or is there some intrinsic,
magical reason I'm missing?

-marc

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2003\07\08@084746 by hael Rigby-Jones

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> -----Original Message-----
> From: Marc Nicholas [SMTP:spam_OUTmarcTakeThisOuTspamGEEKYTHINGS.COM]
> Sent: Tuesday, July 08, 2003 1:39 PM
> To:   .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject:      [EE]: Phototransistors (*holding my head in shame*)
>
> This is probably a really, really dumb question...and probably a result of
> my lack of formal electronics education ;-)
>
> Why do three pin phototransistors exist? Is it purely for
> aesthetics/standardized packaging reasons, or is there some intrinsic,
> magical reason I'm missing?
>
> -marc
>
For biasing to improve either sensitivity or speed.  Phototransistors used
without any base connection are very slow.  By providing a dc path from the
base, the charge in the BE junction can be removed more quickly, speeding up
the transistor at the cost of reducing sensitivity.

Mike


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2003\07\08@084754 by p.cousens

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If it had two pins it would be called a photo diode (just kidding)
So you can adjust the biasing
Change gain etc
Useful in control loops

Peter Cousens
.....cousensKILLspamspam.....biscit.biz

> {Original Message removed}

2003\07\08@092034 by Marc Nicholas

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That actually makes complete sense! :-)

So I'm fine to use a 3-pin version in a circuit that would normally use a
2-pin version...as long as I leave base N/C?

-marc

On 8/7/03 08:47, "Michael Rigby-Jones" <EraseMEMichael.Rigby-Jonesspam_OUTspamTakeThisOuTBOOKHAM.COM>
wrote:

>> {Original Message removed}

2003\07\08@110040 by Mike Singer
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p.cousens wrote:

> If it had two pins it would be called a photo diode...

2-pin phototransistors were more common than 3-pin in my
experience.

As example:

http://sharp-world.com/products/device/ctlg/esite23/table/072.html


Mike.

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2003\07\08@112539 by Mike Hord

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>So I'm fine to use a 3-pin version in a circuit that would normally use a
>2-pin version...as long as I leave base N/C?

No, I don't think that would be wise.  You'd pick up all kinds of
environmental noise on that pin, which would impact the biasing
making it more or less sensitive at random.  You would probably
be better tying it to ground; I'm not positive about that, though.

Mike H.

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2003\07\08@113813 by Marc Nicholas

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Might be better to acquire a 2-pin phototransistor, then ;-)


-marc


On 8/7/03 11:24, "Mike Hord" <gaidinmdspamspam_OUTHOTMAIL.COM> wrote:

{Quote hidden}

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2003\07\08@114051 by Marc Nicholas

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On 8/7/03 10:59, "Mike Singer" <@spam@msingerKILLspamspamPOLUOSTROV.NET> wrote:

>> If it had two pins it would be called a photo diode...
>
> 2-pin phototransistors were more common than 3-pin in my
> experience.

I concur with that...I've only ever dealt with the 2-pin variety before,
which is why the 3-pin variety kinda had me wondering.

-marc


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UNIX, Database, Security and Networking Consulting

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2003\07\08@130247 by John Ferrell

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I woud expect it to work if you tie the base back to the collector supply
through a 100k resistor. That may provide too much gain for a circuit
intended for a diode.

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
KILLspamjohnferrellKILLspamspamearthlink.net
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"

----- Original Message -----
From: "Marc Nicholas" <RemoveMEmarcTakeThisOuTspamGEEKYTHINGS.COM>
To: <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Sent: Tuesday, July 08, 2003 9:18 AM
Subject: Re: [EE]: Phototransistors (*holding my head in shame*)


> That actually makes complete sense! :-)
>
> So I'm fine to use a 3-pin version in a circuit that would normally use a
> 2-pin version...as long as I leave base N/C?
>
> -marc
>
> On 8/7/03 08:47, "Michael Rigby-Jones" <TakeThisOuTMichael.Rigby-JonesEraseMEspamspam_OUTBOOKHAM.COM>
> wrote:
>
> >> {Original Message removed}

2003\07\08@160442 by p.cousens

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If it had two pins it would be called a photo diode (just kidding)
If you're gonna quote me, quote me
Doesn't take much longer of your attention span

Peter Cousens
RemoveMEcousensspamTakeThisOuTbiscit.biz

> {Original Message removed}

2003\07\09@021933 by Mike Singer

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p.cousens wrote (full version as requested:-)
> Sent: Wednesday, July 09, 2003 12:05 AM
> To: PICLISTEraseMEspam.....MITVMA.MIT.EDU
> Subject: Re: [EE]: Phototransistors (*holding my head in shame*)
>
> If it had two pins it would be called a photo diode (just kidding)
> If you're gonna quote me, quote me
> Doesn't take much longer of your attention span
>
> Peter Cousens
> EraseMEcousensspambiscit.biz
>
> > {Original Message removed}

2003\07\09@123846 by Peter L. Peres

picon face
>>> If it had two pins it would be called a photo diode...
>>
>> 2-pin phototransistors were more common than 3-pin in my
>> experience.
>
>I concur with that...I've only ever dealt with the 2-pin variety before,
>which is why the 3-pin variety kinda had me wondering.

Hehe. 3-pin phototransistors were the most common in hobbyist times
because that's what you set if you carefully saw off the top of a metal
can transistor like 2N2222 ;-)

Peter

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2003\07\09@151108 by Steve Smith

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A more simple soulition than sawing the top off :-
OC71 scrape the paint off and you have an OCP71

(maybe 30 years ago)

Steve......

{Original Message removed}

2003\07\09@152928 by Marc Nicholas

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Shades of using EPROMs as crude input devices ;-)


-marc

On 9/7/03 15:10, "Steve Smith" <RemoveMExygaxspam_OUTspamKILLspamBLUEYONDER.CO.UK> wrote:

> A more simple soulition than sawing the top off :-
> OC71 scrape the paint off and you have an OCP71
>
> (maybe 30 years ago)
>
> Steve......
>
> {Original Message removed}

2003\07\09@155623 by John Ferrell

face picon face
I had not heard of the the EPROM bit, Please enlighten me.

I have used a LED as a photodiode.

John Ferrell
6241 Phillippi Rd
Julian NC 27283
Phone: (336)685-9606
RemoveMEjohnferrellTakeThisOuTspamspamearthlink.net
Dixie Competition Products
NSRCA 479 AMA 4190  W8CCW
"My Competition is Not My Enemy"

----- Original Message -----
From: "Marc Nicholas" <EraseMEmarcspamspamspamBeGoneGEEKYTHINGS.COM>
To: <RemoveMEPICLISTKILLspamspamMITVMA.MIT.EDU>
Sent: Wednesday, July 09, 2003 3:28 PM
Subject: Re: [EE]: Phototransistors (*holding my head in shame*)


{Quote hidden}

> > {Original Message removed}

2003\07\09@160132 by Marc Nicholas

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Actually, maybe it was ROM chips...but, anyways, back in ceramic casing days
you could file away the casing and make a crude imaging array.


-marc


On 9/7/03 15:56, "John Ferrell" <spamBeGonejohnferrellSTOPspamspamEraseMEEARTHLINK.NET> wrote:

{Quote hidden}

>>> {Original Message removed}

2003\07\09@170119 by Olin Lathrop

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> Actually, maybe it was ROM chips...but, anyways, back in ceramic casing
> days you could file away the casing and make a crude imaging array.

Dr. William Yerazunis of the Mitsubishi research center in Cambridge
Massachusetts has used this concept to develop a low cost imaging array
from dynamic RAM circuits.  These things are now in production and are
used as cheap image arrays in toys and low end devices.  They also have an
exponential response, which is useful in dealing with the large dynamic
range of brightness the human eye can interpret.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2003\07\09@203422 by Mike Singer

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Resending "onlist"
(Hope Peter Cousens doesn't mind it :-)

----------------------------
p.cousens wrote:
> (just kidding)
> do you have a phrase book?

Sorry if my posts looked a bit offensive.

Mike.

P.S. Any links to good phrase books?
----------------------------

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2003\07\10@014438 by Wouter van Ooijen

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> Actually, maybe it was ROM chips...but, anyways, back in
> ceramic casing
> days you could file away the casing and make a crude imaging array.

IIRC this was described in a Circuit Cellar article long long ago, when
Byte was still the leading computer magazine.

Wouter van Ooijen

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2003\07\10@033621 by hael Rigby-Jones

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> -----Original Message-----
> From: Mike Hord [SMTP:.....gaidinmdspamRemoveMEHOTMAIL.COM]
> Sent: Tuesday, July 08, 2003 4:25 PM
> To:   RemoveMEPICLISTspamspamBeGoneMITVMA.MIT.EDU
> Subject:      Re: [EE]: Phototransistors (*holding my head in shame*)
>
> >So I'm fine to use a 3-pin version in a circuit that would normally use a
> >2-pin version...as long as I leave base N/C?
>
> No, I don't think that would be wise.  You'd pick up all kinds of
> environmental noise on that pin, which would impact the biasing
> making it more or less sensitive at random.  You would probably
> be better tying it to ground; I'm not positive about that, though.
>
> Mike H.
>
Tying the base to ground would stop the transistor ever switching on!  The
OP's circuit will probably work fine with the base open, but if it's
operating in a noisy environment, it may be better to try and source a part
without the base connection.

Mike


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2003\07\10@033824 by Robert Rolf

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No, it was early dynamic RAM chips.
The charge in the memory cells leaks off more quickly when exposed to light.
Early DRAM chips had a refresh cycle that was separate from the read cycle.
You'd write all 1's to the chip, then repeatedly read the array without refresh.
The cells that changed to 0's first had the highest brightness.
Byte Magazine even had a construction article and code to make
a simple B&W imager, long before CCD's or web cams existed.

members.tripod.com/RoBoJRR/techcorner.htm
"The September and October 83 issues of Byte Magazine contain an in depth
article on building a camera based on Micron's OpticRam. Technology guru,
Steve Ciarcia, provides not only a highly detailed description
of the technology involved, but complete schematics and software listings as well.
This fine article is included in his Circuit Cellar Inc. series as well and
may be easier to find than the original Byte articles."

Marc Nicholas wrote:
{Quote hidden}

Oops, you just infringed an AT&T patent.

Seems that a Popular (Radio?) Electronics columnist wrote in the late 70's
an article about doing exactly that,
to experiment with bidirectional communication over the 'new'
optical fibre technology.

AT&T lawyers showed up with the police to execute a search warrant on
his home, claiming that he must have committed industrial espionage in
order for him to have written about their yet to be obtained patent.
The columnist was so pissed off that he dedicated half his column to slamming
their strong arm tactics.  I think it was Don Lancaster, but I'm not certain.

R
{Quote hidden}

> >>> {Original Message removed}

2003\07\10@050554 by Alan B. Pearce

face picon face
>Shades of using EPROMs as crude input devices ;-)

Never heard of that happening, but I have heard of people taking the top
cover off ceramic package 16k dynamic ram chips to use them as image sensors
before CCD and CMOS sensors became available.

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2003\07\10@102430 by Mike DeMetz

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This was done using dynamic RAM chips. The ceramic one with the metal caps were
the easiest to mod. Your program wrote to 1's to each bit, then you scanned through
memory loking for 0's caused bt light exposure.
> Actually, maybe it was ROM chips...but, anyways, back in ceramic
> casing days you could file away the casing and make a crude imaging
> array.
>
>
> -marc

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2003\07\11@162758 by Dwayne Reid

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At 01:36 AM 7/10/03 -0600, Robert Rolf wrote:

>Oops, you just infringed an AT&T patent.
>
>Seems that a Popular (Radio?) Electronics columnist wrote in the late 70's
>an article about doing exactly that,
>to experiment with bidirectional communication over the 'new'
>optical fibre technology.
>
>AT&T lawyers showed up with the police to execute a search warrant on
>his home, claiming that he must have committed industrial espionage in
>order for him to have written about their yet to be obtained patent.
>The columnist was so pissed off that he dedicated half his column to slamming
>their strong arm tactics.  I think it was Don Lancaster, but I'm not certain.

Actually, it was Forrest W Mimms III.  Many will recognize the name from
his "Engineer's Notebook" series often seen at Radio Shack.

dwayne

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2003\07\11@165045 by Marc Nicholas

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On 11/7/03 15:38, "Dwayne Reid" <RemoveMEdwayner@spam@spamspamBeGonePLANET.EON.NET> wrote:

>> AT&T lawyers showed up with the police to execute a search warrant on
>> his home, claiming that he must have committed industrial espionage in
>> order for him to have written about their yet to be obtained patent.
>> The columnist was so pissed off that he dedicated half his column to slamming
>> their strong arm tactics.  I think it was Don Lancaster, but I'm not certain.
>
> Actually, it was Forrest W Mimms III.  Many will recognize the name from
> his "Engineer's Notebook" series often seen at Radio Shack.

Yeah, I have some of his booklets!!! Memories of when Radioshack actually
sold some worthwhile products ;-)


-marc

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UNIX, Database, Security and Networking Consulting

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2003\07\15@051821 by Dwayne Reid

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At 01:36 AM 7/10/03 -0600, Robert Rolf wrote:

>Oops, you just infringed an AT&T patent.
>
>Seems that a Popular (Radio?) Electronics columnist wrote in the late 70's
>an article about doing exactly that,
>to experiment with bidirectional communication over the 'new'
>optical fibre technology.
>
>AT&T lawyers showed up with the police to execute a search warrant on
>his home, claiming that he must have committed industrial espionage in
>order for him to have written about their yet to be obtained patent.
>The columnist was so pissed off that he dedicated half his column to slamming
>their strong arm tactics.  I think it was Don Lancaster, but I'm not certain.

Actually, it was Forrest W Mimms III.  Many will recognize the name from
his "Engineer's Notebook" series often seen at Radio Shack.

dwayne

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