Atmel AVR1925 XMEGA-C3 Xplained, User Manual

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AVR1925: XMEGA-C3 Xplained Hardware User’s Guide [APPLICATION NOTE]
Atmel-42053B-XMEGA-C3-Xplained-Hardware-Users-Guide_Application-Note_AVR1925_02/2015
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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
Table 4-10 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 .
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