Ambient Light Sensor Board

A project log for Simple LED Matrix Alarm Clock

A Fairly Conventional Alarm Clock using LED Matrix Displays

bharbourBharbour 03/14/2023 at 21:270 Comments

In a previous project that used more of the display modules, I used a multiplexer board to separate 12 matrix character displays into 3 different segments of one I2C bus. That multiplexer board has a single ambient light sensor on the back side. The ambient light sensor that I used has been completely unavailable for the last 2 years, so I laid out a new board with two sites for different sensors from different vendors. Both sensors communicate with the host via I2C and have different addresses so they could both be populated on the same board if you wanted to. One sensor is enough for complete function though.

Reading the ambient light level makes it possible for the system software to automatically dim the displays so it does not light up a dark room, but still maintains a bright enough image in a well lit room to be readable. 

This system is using the Vishay VEML7700 sensor which does not have an interrupt output. Strangely, the LTR303ALS-01 interrupt only indicates that the light level is out of a programmed range, rather than the conversion complete function I would prefer.