IR sensors too noisy

I was using an IR transmitter for illumination

That 'black/white' distinction may not exist in the IR wavelength. Hence, your poor signal to noise ratio. Better to use visable light here.

Luhan

What light source are you using to illuminate the B/W object?

Not nearly enough information.

By IR transmitter, do you mean some prepackaged device that might include modulation, or just an IR LED fed by DC?

Modulating the source, and amplifying the detector signal through a narrow bandpass filter is a common way to reject interfering signals, like room lighting.

Do you have control over the surface of the black and white objects? If so, replacing the white with retro reflective tape can increase the contrast dramatically. This is especially true of the surfaces are a significant distance from the source and detector. If the distance is very small, it is difficult to get the source and detector close enough that the retroreflected light ends up on the detector, instead of on the source.

Is your detector filtered to block most visible light? IR LEDs come in two common types, 880 nm and 940 nm. The 880's often have higher output, but the 950's are close to the long wave limit for silicon detectors. So the 950's allow slightly better short wave blocking with only a narrow band of wavelengths that get through that can be detected by silicon between the filter's passband, and silicon's long wave limit.

What is the room lighting - fluorescent tubes are bad news, for instance.

Try the system in a darkened room. If most of the interference disappears you know where its coming from...

Make sure that your IR sensor has a built in filter (typically they are moulded in what looks like black plastic)

There is a small possibility that the B/W target you are using may not be Black and White when seen at IR wavelengths. Try different materials.

If the response is still poor, then you need some or all of:-

Reduce interference by shielding from direct and reflected room light

Stronger transmitted signal (=>higher current into IR LED, but watch dissipation.)

Optics to concentrate signal onto a smallish area

Reduce distance between transmitter and receiver (inverse square law applies)

Increase signal into detector (use a lens to gather more IR)

In the long term this kind of thing is best done by pulsing the transmitter and using an AC amplifier with synchronous detection.

Have fun ! Dave

Yes, you should modulate your light source to get rid of the ambient light.

Rene