Appendix C: General Application
Guide for APDS-9002
The amount of converted voltage,
VOUT, is mainly dependant
Brightness is measured as “LUX”
unit, which describes how intense
a light source that our eyes
perceive. LUX meter is the
equipment for “LUX”
measurement. Light sources with
the same LUX level appear at the
same brightness to the human
eyes.
proportionally on the photo
current which is generated by the
brightness of the light shone on
the photo sensor and the load
resistor used, RL. Increasing the
brightness of the light and/or the
load resistor will increase the
output voltage.
The APDS-9002 is a low cost
analog-output ambient light photo
sensor which spectral response
closely emulates the human eyes.
APDS-9002 consists of a
phototransistor that enables the
photo sensor to produce a high
gain photo current to a sufficient
level that can be converted to
voltage with a standard value of
external resistor. APDS-9002 is
then easily integrated into
V
V
CC
CC
2
3
systems that use ADC input which
is available for sampling of the
external source, as shown in
Figure 14 below.
LIGHT
SOURCE
V
1
OUT
APDS-9002
A/ D
C
R
L
4
MICRO-
CONTROLLER
NC
Figure 14. Configuration of APDS-9002 being used directly.
10
Selection of the load resistor RL
will determine the amount of
current-to-voltage conversion in
the circuit. Based on Figure 14
and using white LED as the light
source, measurement has been
carried out by using different
load resistors to examine the
variation of the output voltage
towards the intense of LUX. The
result is shown in Graph 1.
APDS-9002 allows output
T = 25°C
A
V
= 3 V
CC
LIGHT SOURCE: WHITE LED
1
0.1
R = 1 kW
0.01
0.001
R = 5.1 kW
R = 11 kW
R = 51 kW
10
100
1000
voltage hits around 2.3 V, after
this it saturates.
LUMINANCE, Ev (LUX)
Light source, e.g., fluorescent
light, consists of ac noise about
100 Hz frequency. A capacitor of
10 µF, which acts as a low-pass
filter, is recommended to add in
parallel with resistor to by-pass
the ripples.
Graph 1. Output voltage vs. luminance at different load resistor.
14
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