need a reflecting light sencor "help Please!!!!&quo

[directcurrent]

Hay folks, I've got a pickled! of a problem!

I need a sencor circuit that sends a small light beam on 6 to 10 inches, reflect off a small mirror to a receiver sencor, maybe a half inch to its sender, when the circuit senses the beam is not there it would send either a high or low signal to a and gate, theere by letting me know there is something there blocking the path. the beam needs to be such that it is not interfeared by standard son light.

I welcome any ideas on circuits that would do the trick. God bless you many days ahead. DC.

[JPKNHTP]

-JPKNHTP

[rshayes]

If there is a lot of light present, you will probably want to modulate the transmitted beam. With an LED as a transmitter, this can easily be done by modulating the drive current. A frequency in the tens of kilohertz is fairly reasonable.

The modulated source allows the receiver to be AC coupled. This allows the transmitted beam to be separated from the sunlight, which is probably much stronger.

The received signal will need some amplification. It can then be rectified and filtered to get a DC signal suitable for logic.

You can probably find detailed descriptions of this type of sensor in the application notes published by either the LED or photodiode manufacturers. I would try looking at the Agilent (formerly Hewlett Packard) web site, since at one time Hewlett Packard published an entire book of optoelectronic application information.

A normal LED running at 5 or 10 milliamps would probably provide enough light. An infrared or red LED would be the best match to a silicon photodiode. The other visible LEDs may be more expensive and probably wouldn't work as well.

A three lead phototransistor may be the easiest detector to get. The base connection alows you to bled out the constant photocurrent from the sunlight before it gets apmlified and overloads the receiver.

[rshayes]

It seems that the LED operations that were originally Hewlett Packard became part of Agilent but have been transferred to Avago Technologies (www.avagotech.com).

One of their application notes (AN 1040) describes a modulated sensor system.

[jimandy]

Consider using something other han a mirror to bounce back the light. 3M reflective tape is a good choice.

[MicroRem]

One of our older pieces of equipment (early to mid 80's) used a system exactly like that, although the distance was across a few feet of moving conveyor belt, instead of a few inches. The transmitter/receiver was one unit, built by Micro Switch, USA, Part number FEMLS7A 1011. We used a white bicycle type reflector for the target, a miiror required too precise an alignment. The 3m retro tape is a great idea. One problem we had with the system was that somtimes shiny objects fooled the sensor by reflecting back enough light to keep the sensor from trippping. The unit is a bit of a beast by todays standards, It measures about 4" x 2" x 1". It ran on 12 to 18 VDC and provided N/O contacts all in one unit. I don't know what you app is exactly, but if you want a used one email your address and i'll mail it. I would not recommend it for a critical application or something you plan on marketing, but if it's a one off project it might work for you.


Just my $.02...

regards

Tom

[philba]

Originally posted by stephen:
If there is a lot of light present, you will probably want to modulate the transmitted beam. With an LED as a transmitter, this can easily be done by modulating the drive current. A frequency in the tens of kilohertz is fairly reasonable.

The modulated source allows the receiver to be AC coupled. This allows the transmitted beam to be separated from the sunlight, which is probably much stronger.

The received signal will need some amplification. It can then be rectified and filtered to get a DC signal suitable for logic.

You can probably find detailed descriptions of this type of sensor in the application notes published by either the LED or photodiode manufacturers. I would try looking at the Agilent (formerly Hewlett Packard) web site, since at one time Hewlett Packard published an entire book of optoelectronic application information.

A normal LED running at 5 or 10 milliamps would probably provide enough light. An infrared or red LED would be the best match to a silicon photodiode. The other visible LEDs may be more expensive and probably wouldn't work as well.

A three lead phototransistor may be the easiest detector to get. The base connection alows you to bled out the constant photocurrent from the sunlight before it gets apmlified and overloads the receiver.

I was typing in something very similar last night when the power went out until 3AM.

It's not clear if this is an industrial application or a home-brew type. I'll assume home-brew.

Anyway, modulation is a good way to reject falses. You can get little IR receivers that expect a carrier (38khz - 42 khz) is typical. that simplifies the detection of the carrier and rejection of everything else. Radio shack has one here and the surplus houses typically have several to choose from. Look for IR receiver as the keywords. You might need a little glue logic to latch up the carrier for your indicator circuit. You can use a 555 to generate the carrier and drive an IR LED. I'd use an LED with a reasonably tight beam (though not too tight to make aiming possible). Try to match the LED wavelength to the receiver's although it's not super critical. The stronger (i.e. more light output) the LED, the better. a little experimentation with the device may be necessary.

If you are uC savy, you could also put a code on the modulated beam and look for that at the receiver to further increase false rejection or allow multiple units to be used.

Phil

[Engineer1138]

I'm actually doing exactly this right now, but my required distance to the reflector is less than an inch.

I use the PT/GL 4800 LED/phototransistor pair (Sharp, I think) and it's OK, but alignment is more critical than I like, I think due to the lens on the LED. I may go to a different LED that will diffuse the light a bit more. Pretty simple circuit: just follow the examples in the datasheet.

Oops: just noticed that in your case there's sunlight (I skipped the "son" part before , so my version probably won't work.

<small>[ March 02, 2006, 09:39 AM: Message edited by: Engineer1138 ]</small>

[directcurrent]

Thank you Phi--- and Eng 1138 Woops, just kiding,and all you other folk Those ideas will give me a good start in a solution. your right this a home brew needed device for something for my disabled mother to help her with some problems. I need something with 6 to 9 volts input, modulation sounds like what i want to do here and the reflective tape sounds much better then a mirror.
Thank you again and I welcome more ideas

God bless you and your families days ahead. DC

Woops!, found a problem, so I will have to put things on hold for a few days, it call Gallstones and Kidney stones at the same time. Got any help for that Folks? "outch, they hurt!!!"

[Gorgon]

Hi,
I know of gallstones, and they ar not the same as kidney stones! Had to remove my gallbladder because of the stones. I don't think you do the same with kidneys

TOK

[directcurrent]

Hi Gorgon, The gallstones, they remove the whole bladder, but the kidneystones>>they use ultra sound waves to break it up if it is in the right place, if not, they have to insert a tube up the penial tube that has a micro tool which grabs it and pulls it out thru the penial tube. depending on the size of the stone. Some of them stones can get as big as a small plum. My is the size of a grape. What really hurts is the back pressure built up by the stone plugging the Piss behind it. Makes you feel like Godzilla step on your ducess a few times.

By the way folks, You gave me an idea with the sencor. I made a call to Re-didio-Shack and got the IR receiver Module. After relizing what I was working on. I bought a ceap laser pointer and some reflective tape, dismatled the pointer and modified its shape to fit, place the reflective tape where I wanted it and the receiver and it work prefectt-to the first time. Thanks Folks. Wish my dating life was has easy to fit as that. God bless and many thanks. DC.