Light Dimmer with Capsense Brightness Control

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T delay
T/2
3T/8
connectors, located at the opposite board sides. The PCB
Gerber files are provided in the supporting archive
together with PSoC project can be used for PCB routing
reference. Figure 9 shows different Light Dimmer photos.
Figure 9. Light Dimmer Photos
a) Front View
T/4
T/8
0
0
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
N slid
b) Back View
Figure 8. Triac Turning on Delay vs. Slider Position
AC Mains Frequency Calibration
There are several frequency AC standards in the world;
some countries use 50Hz frequency, other 60Hz. For
dimmer operation ability worldwide without any manual
adjustments, the additional calibration procedure is
implemented. This procedure measures the actual AC
mains frequency and calculates a scale coefficient to
transform the lookup table array in the actual triac turning
on delay values. The calibration procedure is initiated
once after dimmer power up.
Calibration takes in three stages. At first stage the duration
of AC half period is measured using a CSD UM counter
block. The 32 measurements are taken, averaged value is
calculated. For this purpose a CSD is manually
reconfigured by re-routing counter enable signal from
comparator bus to zero-cross detector output.
At the second stage the scale coefficient is calculated as
relation of measured period (T C) to expected period (T C50)
for 50Hz AC:
K
T
T
C
= Equation 1
C 50
At third stage the triac turning on delay table (baConst) are
scaled by coefficient K.
Dimmer Mechanical Construction
The dimmer is composed from two boards. The LED array
and Capsense slider are placed on the first board, only
SMT components are placed on this board. The reverse
mount LEDs were placed in the slider segments.
The power supply, zero-crossing detector, triac and screw
power/lamp connectors were placed on second board. All
through hole components were located on this board as
well. The boards were connected together using 2
Safety Warnings
c) Side View
The Light Dimmer does not have galvanic isolation from
AC Mains Line. Plastic overlay should have thickness
more than 2mm for user electrical shock preventing.
Please newer touch PCB or dimmer components when
supply voltage is applied. For device debugging and
testing, please use the isolation transformer or galvanically
isolated scope probes.
Possible Modifications
Some customers are willing optimizing the dimmer price
for cost sensitive applications. The most expensive part is
switching DC-DC converter. To reduce BOM amount, the
power supply can be redesigned by using the simplest
capacitive current source, see
January 10, 2008 Document No. 001-08990 Rev. *B (AN# is same as last 5 digits of doc #.) 4