Searching \ for '[OT] Need help with phototransistor' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/index.htm?key=need+help+with+phototransistor
Search entire site for: 'Need help with phototransistor'.

Exact match. Not showing close matches.
PICList Thread
'[OT] Need help with phototransistor'
1998\04\08@164213 by Hardy e/ou Rafael Pinto

flavicon
face
   Hi guys,

   I need help on using a phototransistor (PT, for short!) to excite an
input pin on a PIC16F84. I am using the typical circuit, that is, the PT
with emmiter grounded and collector connected to the i/o pin. I put a
pull-up resistor of 10k from the i/o pin to Vdd. It didn't worked! I am
using a TIL78 activated by a LED (yellow). Can anyone suggest other
cirucuit?

   Rafael Pinto



          Vdd
         |
         >
         > 10k
         >
         |
         +-------------> RA0
         |
      | /
      |/     TIL78
      |\
      | \|
        -|
         |
         |
       -----
        ---
         -

1998\04\09@100030 by John Shreffler

flavicon
face
part 0 876 bytes
-----Original Message-----
From:   Hardy e/ou Rafael Pinto [SMTP:spam_OUTcppintoTakeThisOuTspamNETRIO.COM.BR]
Sent:   Wednesday, April 08, 1998 4:18 PM
To:     .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
Subject:        [OT] Need help with phototransistor

   Hi guys,

   I need help on using a phototransistor (PT, for short!) to excite an
input pin on a PIC16F84. I am using the typical circuit, that is, the PT
with emmiter grounded and collector connected to the i/o pin. I put a
pull-up resistor of 10k from the i/o pin to Vdd. It didn't worked! I am
using a TIL78 activated by a LED (yellow). Can anyone suggest other
cirucuit?

   Rafael Pinto



          Vdd
         |
         >
         > 10k
         >
         |
         +-------------> RA0
         |
      | /
      |/     TIL78
      |\
      | \|
        -|
         |
         |
       -----
        ---
         -

1998\04\09@145110 by Mike Keitz

picon face
On Thu, 9 Apr 1998 10:01:40 -0400 John Shreffler <johnsspamKILLspamAVENUETECH.COM>
writes:
>------ =_NextPart_000_01BD639E.817F5430
>Content-Type: text/plain; charset="us-ascii"
>Content-Transfer-Encoding: 7bit
>
>PTs are sensitive to IR, in the 800 to 950 nm range, and
>would ignore the yellow.  Try an IR emitter instead.

The PT's in clear plastic packages are sensitive to all wavelengths from
950 nm IR through blue, and even some UV.  They are *most* sensitive to
IR (being about 50% down at blue).  Many PT's are packaged in "black" or
very dark green plastic that absorbs visible light but still transmits
IR.  These of course have to be used with IR emitters.

IR emitters are also much brighter than regular LED's.  So unless there's
some particular reason to use yellow, change to red or IR.


_____________________________________________________________________
You don't need to buy Internet access to use free Internet e-mail.
Get completely free e-mail from Juno at http://www.juno.com
Or call Juno at (800) 654-JUNO [654-5866]

1998\04\09@171430 by Sean Breheny

face picon face
At 12:23 PM 4/9/98 -0400, you wrote:
>The PT's in clear plastic packages are sensitive to all wavelengths from
>950 nm IR through blue, and even some UV.  They are *most* sensitive to
>IR (being about 50% down at blue).  Many PT's are packaged in "black" or
>very dark green plastic that absorbs visible light but still transmits
>IR.  These of course have to be used with IR emitters.
>
>IR emitters are also much brighter than regular LED's.  So unless there's
>some particular reason to use yellow, change to red or IR.
>

Mike,

I have been looking for blue and green sensitive PTs for quite a while. I
was not successful in finding them, even in the clear packages. Most of the
ones I have seen have not responded very well to green or blue light. It
was a while back and I'm not sure I remember correctly, but I think I took
a blue LED and pointed it directly into a clead PT with no distance between
them and the PT acted as if the led weren't there. A green LED didn't do
much better. Red and IR affected it greatly.

Sean

+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
Fight injustice, please look at
http://homepages.enterprise.net/toolan/joanandrews/

Personal page: http://www.people.cornell.edu/pages/shb7
.....shb7KILLspamspam.....cornell.edu
Phone(USA): (607) 253-0315

1998\04\10@032046 by Michael Ghormley

flavicon
face
Subject: [OT] Need help with phototransistor

Rafael Pinto wrote:

<SNIP>
>  I am using a TIL78 activated by a LED (yellow). Can anyone suggest
>  other cirucuit?

This is just my guess, but most phototransistors are more sensitive to
red and IR light.  Perhaps your yellow LED isn't being seen by the PT.

Either switch to red, or if you can't for some reason, then a photodiode
might be a better choice as they usually are sensitive to shorter
wavelengths.  I have seen an advertisement for photodiodes down to 214nM.

Remember though, that in general a photodiode will produce less
photocurrent than a phototransistor (roughly the same detectivity,
though).  If the light from the LED is weak, then you might have to hook
up to additional circuitry to detect the LED.

Just my thoughts.  Your mileage may vary.

Michael

REMOVE THE .NS (NO SPAM) FROM MY ADDRESS TO REPLY
*****************************************
The strong do what they have to do and
the weak accept what they have to accept.
                            --Thucydides

1998\04\10@111734 by Martin R. Green

flavicon
face
Just a question...

Aren't LED's supposed to be able to work as photodetectors?  If so,
has anyone tried using a blue LED as a detector of the light from
another blue LED?  Of course, this might be a complete waste of time,
but I just wondered.

CIAO - Martin.


On Thu, 9 Apr 1998 17:13:17 -0400, Sean Breheny <EraseMEshb7spam_OUTspamTakeThisOuTCORNELL.EDU>
wrote:

{Quote hidden}

Martin R. Green
elimarspamspam_OUTNOSPAMbigfoot.com

To reply, remove the NOSPAM from the return address
Stamp out SPAM everywhere!!!

1998\04\15@211116 by Larry G. Nelson Sr.

flavicon
face
I used a blue enhanced photodiode. I then added a gain stage. This worked
well with a blue LED as well as a "Pure Green" LED.

At 05:13 PM 4/9/98 -0400, you wrote:
{Quote hidden}

Larry G. Nelson Sr.
KILLspamL.NelsonKILLspamspamieee.org
http://www.ultranet.com/~nr

1998\04\19@174059 by Andrew Russell Morris

picon face
At 05:17 PM 4/8/98 -0300, you wrote:
{Quote hidden}

I've been doing this for about 3 years without problems. I use a 33k to
100k pull DOWN resistor, instead of a pull up resistor. I think the
threshold voltage, with 5Vcc is about 1.8 volts.

More... (looser matching)
- Last day of these posts
- In 1998 , 1999 only
- Today
- New search...