AVR1925: XMEGA-C3 Xplained Hardware User’s Guide [APPLICATION NOTE]
Atmel-42053B-XMEGA-C3-Xplained-Hardware-Users-Guide_Application-Note_AVR1925_02/2015
12
4.6.2 Ambient Light Sensor
The ambient light sensor TEMT6000X01 from Vishay Semiconductors is sensitive to visible light much like the human
eye. The measurement circuitry is configured to measure the illuminance from ~10 to ~900lx when the internal VCC/1.6
reference is used.
The data in
which shows the relationship between illuminance and output voltage of the sensor circuitry is
generated based on the symbols and formulas in
Table 4-9. Symbol Description for Illuminance Calculation
Symbols
Description
ICA
Calibrated sensor responsivity at 100lx. This is 50µA according to the sensor datasheet
Ev
Illuminance
I
Current through the sensor
U
Output voltage of the sensor circuitry that is provided to the ADC
R
Series resistor of the sensor circuitry. 4.7kΩ has been chosen in this design
Ev = 100 × I / ICA
Illuminance is calculated based on the relation of the actual current through the sensor to the
calibrated value at 100lx
I = U / R
Since the ADC measures the voltage across the series resistor of the sensor circuitry it is
necessary to calculate the voltage based on the current
U = (Ev × R × ICA) / 100
Based on the current and the illuminance the output voltage of the sensor circuitry can be
calculated
Table 4-10. Illuminance vs. ADC Input Voltage
Illuminance [lux]
ADC input [V]
Illuminance
1
0.0024
Dusk
10
0.0235
Dusk
20
0.0470
Dusk
30
0.0705
Dusk
40
0.0940
Dusk
50
0.1175
Living room
60
0.1410
Living room
70
0.1645
Living room
80
0.1880
Living room
90
0.2115
Living room
100
0.2350
Living room
200
0.4700
Office lighting
300
0.7050
Office lighting
400
0.9400
Office lighting
500
1.1750
Office lighting
600
1.4100
Office lighting
700
1.6450
Office lighting
800
1.8800
Office lighting
900
2.1150
Office lighting
1000
2.3500
Overcast day