TSOP way too sensible-- please help

[radu19880625]

Hello to all the robot builders out there 

Please help me with this TSOP problem.  I need 4 proximity sensors and i used TSOP 1738.

The sensor works fine(hooked it up using the datasheet schematics) but i need to detect at 2-3cm and i can't make it go under 10cm.

I need to use this one as it is immune to the external light.


Thanks a lot!

[MrWizard]

Can't you replace a resistor ? I see they use 100 ohm  & 10k resistors in an example circuit, what if you use a 120 ohm for the 100 or 12k for the 10k ?
 

[radu19880625]

well... not so sure about that.

i already droppes  the ir led voltage to the point of not emitting --  and obviously i can't go lower.
now, what can i do about the reciver ?

it's out of the sensitive freq-- taken into account how sensibility drops from the datasheet graph.

now, TSOP's work in binar logic so i don't think the resistors make any diff because i want ro lover the sensibility not the output voltage.
 
Please help, i am going crazy 

[Soeren]

Hi,

A bit of waste using the TSOP1738 (in one "word") for this small distance, but that's your decision.
To decrease sensitivity, reduce incoming light, either by colored filters, (blue will filter most of the IR, green next most, red won't take much), or by a piece of stiff paper laminated with tin foil (to make it opaque to IR) and then making a hole or a slit to reduce the "area" of incoming light hitting the TSOP1738.
Or... Mount both parts in light tight tubes and mount them in an angle so they both meet at the point of interrest.

[radu19880625]

ok... done some filtering today... but i have no good result.

is it a dark blue ? i have a light blues piece of plastic film. but i will try to place more film.
green is a little bit darker and it seemed to work better when doubled.

but, isn't there a electronical way of dropping the TSOP's sensitivity ? ? ?