hey guys i made this proximity sensor but it doesn't seem to work like it should. the led stays on and only get brighter when it senses something. it also only reaches about an inch if that. i have to put my finger right in front almost touching the IR LED. i used 3 AAAs to power it. how could i get it to go from complete off until theres an object in front and how could i get it to reach 5 more inches???

 

hey guys i made this proximity sensor but it doesn't seem to work like it should. the led stays on and only get brighter when it senses something. it also only reaches about an inch if that. i have to put my finger right in front almost touching the IR LED. i used 3 AAAs to power it. how could i get it to go from complete off until theres an object in front and how could i get it to reach 5 more inches???

what sensor do you use? are you using the PIR sensor? if so then get the Datasheet before using the part. I think most of the PIR sensors are powered from 3-15 volts.
check this site
http://www.futurlec.com/PIR_Sensors.shtml

they offer cheap and good parts

 

It would be helpful if you provide us with the details of what you are trying to do with this detector circuit. For example, what range are you expecting to detect whatever object you are trying to detect.

I think you are trying to put together your own reflective IR sensor module. Often the performance of reflective sensors is intentionally limited to short distances. A quarter of an inch from the reflective sensor is about the maximum effective distance. To achieve greater distances requires that you pulse the IR transmitter with their maximum current for a very short period to avoid damaging the IR transmitter.

hgmjr

 

And you should really put some kind of divider in between the detector and emitter, so you will not get any side illumination from the emitter. Having them that close to each other you are basically shinning the IR right into the side of the photo detector.


You should also place the circuit in a housing with some kind of filter lens to block out ambient light from getting to the detector...

B. Morse

 

i got the IR LED from radioshack it came as a pair. i want to use the sensor as a light switch for about 4 or 5 LEDs. how could i get it to have a 4 to 5 inch range? was my schematic correct? i don't really know how to draw them but i'm really tryin to learn.

 

Is it your idea to use this circuit to turn this bank of 4 or 5 LEDs on by waving your hand in the path of the IR reflective sensor circuit you have built?

hgmjr

 

i want the the LEDs to come on when theres an object present, and to turn off when its removed.

 

Hello,

Is it reflective detection or pass through detection?
For reflection you will need more sensitivity.

Bertus

 

i guess reflective. how could i make it more sensitive?

 

Hello,

Perhaps you could try a circuit like in this link:
http://home.cogeco.ca/~rpaisley4/PhotoDetectors.html

It uses an opamp to have a switch level.

Bertus

 

The problem with attempting to extend the range of the reflective sensor is that you end up making the receiver so sensitive that it begins to respond to ambient light.

The typical solution involves pulsing the IR led and then using an ac coupled receiver. Such a design is a good deal more complex.

hgmjr

 

is there a certain op amp i need to use?

 

Hello,

Did you read the header of the page I gave you?

The Photo-detectors on this page use LM339 (Quad) or LM393 (Dual) voltage comparator, integrated circuits to detect the change in voltage across the sensor. For information on Voltage Comparators please see the Voltage Comparator Information page at this site.

To have less influence of the surrounding light you could place the IR led and the IR transistor into seperate tubes.

Bertus

 

where could i get this opamp?

 

Hello,

Digikey and mouser sell them:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM339NFS-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=LM393AN-ND
http://nl.mouser.com/ProductDetail/...LM339N/?qs=sGAEpiMZZMtdAabcSkQOlyyK8zHKG%2bJo
http://nl.mouser.com/ProductDetail/...393N/?qs=sGAEpiMZZMvHdo5hUx%2bJYsTj/gxH%2b4zl

Bertus