User manual
AVR1934
5
8413A-AVR-09/11
which has been linearized is fairly complex, the resulting temperature should only be
regarded as an approximation to the actual temperature.
2.4 Ambient light sensor
An ambient light sensor in available on the Atmel
®
AVR
®
XMEGA
®
-A3BU Xplained,
which is sensitive to visible light, much like the human eye. A resistor is connected in
series with the light sensor providing a voltage proportional to the current passing
through the light sensor. An increasing current gives an increasing voltage across the
series resistor, and this voltage is measured using the XMEGA ADC. Table 2-2
sho
ws the relationship between the ambient light in lux and the voltage measured.
The table also provides some indication of what the different lux values represent in
daily life.
Table 2-2. Illuminance and ADC input voltage
Illuminance [lux] ADC input [V] Illuminance scenario
1
1 0,0024
Full moon overhead at tropical
latitudes
10 0,0243
20 0,0485
30 0,0728
40 0,0971
50 0,1213 Family living room
60 0,1456
70 0,1699
80 0,1941 Hallway/toilet
100 0,2426 Very dark overcast day
200 0,4853
300 0,7279 Office lighting
400 0,9706 Office lighting
500 1,2132 Office lighting
600 1,4559
700 1,6985
800 1,9412
850 2,0625 Overcast day
1
Data obtained from Wikipedia