ldr to serial

M

Matt Jennings

Guest
I am looking to source a quantity of ready made LDR to serial 'devices'. I
am working on an installation where we need to detect if something has been
picked up by a user. We want to be able to detect this via a serial cable
plugged into the computer. We have the software end under control but have
no idea where we can source the hardware.

Any ideas? We want to buy it ready made - so would pay someone to make them
if necessary.

Regards
Matt
 
What is LDR? I assume it is a detector of some kind. What is its
output (discrete, analog, other)?

A PIC or other microcontroller is a very good, reliable and cheap way
to convert just about any kind of real-world input into an RS232
message.

What kind of quality are looking for in the device (looks like COTS or
looks like home-made)?

BRW


On Fri, 19 Mar 2004 16:30:07 -0000, "Matt Jennings"
<mattjenn@hotmail.com> wrote:

I am looking to source a quantity of ready made LDR to serial 'devices'. I
am working on an installation where we need to detect if something has been
picked up by a user. We want to be able to detect this via a serial cable
plugged into the computer. We have the software end under control but have
no idea where we can source the hardware.

Any ideas? We want to buy it ready made - so would pay someone to make them
if necessary.

Regards
Matt
Click to expand...
 
Hi Bennet
I am no electronics expert or even hobbiest so I cannot comment on your
questions. Light dependent resistor - I remembered from school and though it
was what I needed.
From the details below you may be able to correct me.

As I said in my post. I need to be able to detect when a customer picks up
something from a cradle next to a kiosk. I have been looking into this and I
think a simple light/dark LDR with some type of converter can then end up as
a serial cable. We then intend to use a serial to usb converter to allow us
to plug it into a usb port. We don't know how this will affect the software
hence the requirement to build serial output devices.
Initally we would like a price and a prototype to test. If the customer
wished to proceed we would then require up to 170 units.

This link shows pretty much the kind of thing we are after:
http://www.sprinters.zen.co.uk/wilot/project7.htm

The LDR would need to be very similar to that used in listening posts in
music shops. They sit flush with the mounting and when covered or uncovered
'do something'. We would like the sensor to be small and unobtrusive so that
it can be mounted in the cradle. About the size of the end of your little
finger and as shallow as possible so as not to protrude too far from the
rear of the cradle. The cradle would be similar to that which holds a mobile
phone in a car. From the sensor a 1 m (approx) wire would lead to the
circuit board which would need to be encased. Then from that a short wire to
the serial plug which we would plug into the computer.

I hope that makes sense.
Regards
Matthew


"Bennet Williams" <brwilliams@adelphia.net> wrote in message
news:4llp5015vo21vt96s1gn6ju8ooafc5ubdr@4ax.com...
What is LDR? I assume it is a detector of some kind. What is its
output (discrete, analog, other)?

A PIC or other microcontroller is a very good, reliable and cheap way
to convert just about any kind of real-world input into an RS232
message.

What kind of quality are looking for in the device (looks like COTS or
looks like home-made)?

BRW


On Fri, 19 Mar 2004 16:30:07 -0000, "Matt Jennings"
mattjenn@hotmail.com> wrote:

I am looking to source a quantity of ready made LDR to serial 'devices'.
I
am working on an installation where we need to detect if something has
been
picked up by a user. We want to be able to detect this via a serial cable
plugged into the computer. We have the software end under control but
have
no idea where we can source the hardware.

Any ideas? We want to buy it ready made - so would pay someone to make
them
if necessary.

Regards
Matt
Click to expand...
 
"Matt Jennings" <mattjenn@hotmail.com> wrote:

Hi Bennet
I am no electronics expert or even hobbiest so I cannot comment on your
questions. Light dependent resistor - I remembered from school and though it
was what I needed.
From the details below you may be able to correct me.

As I said in my post. I need to be able to detect when a customer picks up
something from a cradle next to a kiosk. I have been looking into this and I
think a simple light/dark LDR with some type of converter can then end up as
a serial cable. We then intend to use a serial to usb converter to allow us
to plug it into a usb port. We don't know how this will affect the software
hence the requirement to build serial output devices.
Initally we would like a price and a prototype to test. If the customer
wished to proceed we would then require up to 170 units.

This link shows pretty much the kind of thing we are after:
http://www.sprinters.zen.co.uk/wilot/project7.htm
Click to expand...
1. Does it have to be an optical sensor?

A microswitch or a magnetic reed switch (requires a magnet in the item
picked up) could also provide an on/off signal.

A light/dark sensor is not as reliable as a modulated IR beam (emitter
on one side of the cradle, sensor on the other side). In this
configuration the beam would be interrupted when the item is in the
cradle and would be sensed when the item is removed. If the item
is IR reflective, the emitter and sensor would both face the item in
the cradle and the reflected beam would be broken when the item is
removed from the cradle.

2. Does it need to be a specific serial signal (as in a character or a group of
characters), or just a high/low to be sensed by the CTS or DSR leads of the
serial port?

If you need specific character(s), then you probably should consider
a PIC that is programmed to send specific data when it receives an
input signal (from the LDR or other sensor). The easiest PIC to use
would be a BASIC Stamp, but they are much more expensive than the
generic PICs that are usually programmed in C.

High/low sensing is much simpler, requiring a few resistors and
capacitors to ensure a good signal.

Using specific characters means that a single PC could monitor multiple
cradles, and respond to the unique code from each cradle. Using the
high/low detection of the serial control leads limits you to a much
smaller number of connections to the PC.

More about me: http://www.jecarter.com/
VB3/VB6/C/PowerBasic source code: http://www.jecarter.com/programs.html
Freeware for the Palm with NS Basic source code: http://nsb.jecarter.com
Drivers for Pablo graphics tablet and JamCam cameras: http://home.earthlink.net/~mwbt/
johnecarter at@at mindspring dot.dot com. Fix the obvious to reply by email.
 
Bennet Williams wrote:
What is LDR? I assume it is a detector of some kind. What is its
output (discrete, analog, other)?
------------------
Click to expand...
A Light Dependent Resistor is a Cadmium Sulfide cell, and it varies
it's resistance with incipient light, however it's response is not
fast, being useful only for things like slow line-following robots
and day-night threshhold detectors for alarms and lighting controls.

If you have one of those nightlights with a cell in it that turns
off the Xmas xtree bulb by day, then you have such a cell used with a
solid state TRIAC switch.

Their performance is to drop from 10K ohms or so in response to
incident light down to as little as 50 or 100 ohms, and they respond
chiefly to the green part of the visible spectrum, though they also
respond to most of the rest of the visible somewhat.

-Steve
--
-Steve Walz rstevew@armory.com ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000's of Files and Dirs!! With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public
 
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