Infrared Proximity and Ambient Light Sensor
Created: Mar 08, 2017
No description available.
Infrared sensors are electronic devices that are used to sense certain characteristics of its surroundings by either emitting or detecting infrared radiation. This reference design utilizes the Silicon Labs’ Si1143 infrared proximity/ambient light sensor. This is an active optical reflectance proximity detector and ambient light sensor whose operational state is controlled through registers accessible through the I2C interface. This touch less sensor IC includes an analog-to-digital converter, integrated high sensitivity visible and infrared photodiodes, digital signal processor, and one, two, or three integrated infrared LED drivers with 15 selectable drive levels.
This circuit design has two separate systems that only share communications and debug connections to the PC. The main components of the first system are the Si1143 sensor, the C8051F931 microcontroller, and the four infrared emitters. The infrared OSRAM SFH4056 emitters are used. These emitters have a power rating of 40mW and a half-angle of 22 degrees. This system is a thumb-scroll implementation that measures the infrared light energy detected by the Si1143 while each of three infrared emitters is independently activated. The infrared light from these emitters will be reflected back to the Si1143 by a thumb that is swiped in proximity to the sensor. The firmware is able to detect different gestures using the infrared sensor. The nine LEDs will change state to indicate what gesture was recognized.
In the second system, the main components are the Si1143 sensor, the C8051F931 microcontroller, and an infrared emitter. This emitter is OSRAM SFH4650 and has a power rating of 45mW and a half-angle of 15 degrees. This system is a long-range implementation that measures the infrared light energy detected by the Si1143 while a single infrared emitter is activated. All three of the Si1143’s LED drivers are connected to the one emitter to allow multiple drivers to activate the emitter at the same time in order to send more current through the emitter than one driver can provide. Driving more current through the emitters can help achieve longer ranges of detection because the infrared LEDs emit more light with more current. The default firmware only uses one driver at the default pulse width to drive the LED. The five LEDs will change state to indicate how much infrared light feedback is being measured.