I wish to build an "electric eye" type circuit to span about 3 feet. I have
been unable to find any schematic except for model railroads which are only a
few inches. I have a Radio-Shack pair (emitter ? detector). The detector
switches a transistor to pick up a small relay, however, I am having
difficulty getting it to work reliable at 20 inches. I am not using any
'modulation' the emitter is on full time. TV / VCR remotes work at 10 feet.

Any suggestion appreciated

John

try a low power laser

(John A Gallagher) writes:

I wish to build an "electric eye" type circuit to span about 3 feet. I have
been unable to find any schematic except for model railroads which are only a
few inches. I have a Radio-Shack pair (emitter ? detector). The detector
switches a transistor to pick up a small relay, however, I am having
difficulty getting it to work reliable at 20 inches. I am not using any
'modulation' the emitter is on full time. TV / VCR remotes work at 10 feet.

To operate under varying ambient light conditions, you will probably need
modulation. The easiest may be to actually use the receiver from a VCR
or TV remote with a modulated IR LED. It may also be desirable to have
a lens to collimate the beam somewhat.

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(BWL) writes:

try a low power laser

Not necessary for only a few feet. At most, a small lens to reduce the
divergence of the LED.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

"Sam Goldwasser" wrote in message
...
(John A Gallagher) writes:

I wish to build an "electric eye" type circuit to span about 3 feet. I
have
been unable to find any schematic except for model railroads which are
only a
few inches. I have a Radio-Shack pair (emitter ? detector). The
detector
switches a transistor to pick up a small relay, however, I am having
difficulty getting it to work reliable at 20 inches. I am not using any
'modulation' the emitter is on full time. TV / VCR remotes work at 10
feet.

To operate under varying ambient light conditions, you will probably need
modulation. The easiest may be to actually use the receiver from a VCR
or TV remote with a modulated IR LED. It may also be desirable to have
a lens to collimate the beam somewhat.


Yeah there should be some suitable circuits out there, just do a search
online for IR transmitter circuit. Could probably make something simple with
a 555 timer, the reciever modules are easy to find, just get a scrapped VCR
or TV.

"John A Gallagher" wrote in message
...
|
| I wish to build an "electric eye" type circuit to span about 3 feet. I
have
| been unable to find any schematic except for model railroads which are
only a
| few inches. I have a Radio-Shack pair (emitter ? detector). The detector
| switches a transistor to pick up a small relay, however, I am having
| difficulty getting it to work reliable at 20 inches. I am not using any
| 'modulation' the emitter is on full time. TV / VCR remotes work at 10
feet.

Go to your public library and look at back copies of Popular Electronics or
Radio Electronics for a construction article. Or search the web.

N

Sears used to sell a kit for their garage door openers that prevented
the door from coming down if a child or pet was blocking a beam across
the bottom of the door opening. It consisted of an emitter on one side
and a detector for the other side. The detector side had a led that
would indicate when it saw the beam. This was used for aiming the
emitter at installation. It would even work on the double-wide doors.
This kit is now required by our local building code for new constuction
doors.

Van Gardner