Hardware Reference
In-Depth Information
There are lots of different luminosity sensors out there, but because you want to wire
it to our trusty friend, the Raspberry Pi, you want to pick something that you can add
to that device easily. Because the Raspberry Pi does not support analog inputs
(without going through a converter first), you need a digital luminosity sensor, with
bonus points for one that the Linux kernel supports natively. Adafruit has just the
thing: the
Taos TSL2561
digital luminosity/lux/light sensor.
What is Lux?
Lux (abbreviated
lx
), is the SI unit for measuring illuminance, described in
terms of one lumen per square meter. It can be measured with a device
logically called a “lux meter.” The full moon is about 1 lux, while direct sun-
light is measured in the range of tens of thousands to >100,000 lux.
Why is this sensor ideal? A few reasons:
• It is a digital sensor, so you can connect it directly to the Raspberry Pi GPIO pins
without any complicated wiring.
• It is precise and can be configured to detect light ranges from 0.1 to 40,000+ lux.
• It contains both infrared and full-spectrum diodes. Most luminosity sensors have
only one type of detection diode, but the TSL2561 can separately measure infra-
red, full-spectrum, or human-visible light.
• It supports I2C (for an explanation of I2C, see
What is I2C?
). This means you can
connect it to the Raspberry Pi GPIO with just four pins.
• It is a low-power component, about 0.5 mA when actively sensing and less than
15 uA when in powerdown mode.
• It is also small, about the size of a U.S. quarter (see
Figure 4-7
).
