Bittybot is known for making really small systems. Here’s one of their larger ones – a 3-direction object sensor, with a 4~6″ (10.16-15.24cm) range. It’s based on the Sharp IS471 sensor, which has a built-in oscillator & driver for the IR LED, and a built-in IR sensor. Here’s the stats:

• 1.90″ x 0.50″ x 0.35″ thick (4.82 x 1.27 x 0.89cm)
• Short-range sensing of up to 4-6″ (10.16-15.24cm)
• On-board “Objected detected” indicator LEDs eases debugging
• High/low digital output for each sensor makes it easy to interface with most microcontrollers
• Digital output goes “low” when an object is in range
• Based on Sharp’s popular IS471F sensor — this sensor modulates the emitter IR LEDs and filters out return signals outside the modulation frequency for increased immunity to false triggering
• 5V operation

Note:

• This is the last production run of this kit. When sold out, they are being retired