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  • Light Dimmer with Capacitive Touch Control

  • Created: Mar 18, 2016

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This circuit is a light dimmer with a capacitive touch control. It can be used in controlling the brightness of a lamp to your preference by changing the voltage waveform applied to it. The circuit is mainly composed of dimmer circuit, host controller and the capacitive touch circuit. With the use of the capacitive touch circuit, mechanical buttons and rotary controls are replaced.

The design uses the SX8633 Capacitive Button Touch Controller from Samtech. It is an ultra low power, fully integrated 2-channel solution for capacitive touch-buttons and proximity detection applications. LEDs are then attached to its GPIO pins to indicate function and dimming level to which the circuit is set. The circuit has seven brightness levels available using seven capacitive sensor pins of the SX8633 device. The blue colored LEDs indicates that the touch control is on and the orange LEDs indicates the brightness level chosen by the user. If a certain level is chosen, the levels lower than it also lights up with the orange LED. The signal, from the touch control, sets a certain time delay before the triac will conduct during half cycle. This data is then sent to a host microcontroller through an I2C bus. The host microcontroller is connected to the dimmer circuit, which is comprised of an MOC3021 photocoupler and a triac. A zero cross detector circuit is also connected to the host microcontroller. This circuit helps the microcontroller to have a reference point to when to turn on the triac. The lower brightness level is selected from the touch controller the more time is allocated to delay the turning on of the triac. After the time delay, the triac conducts thus turning on the lamp. But, only with a part of the AC wave is supplied to the lamp lowering the average voltage across it which then produce a lower brightness.

The circuit has also a 3.3V regulator to supply the capacitive touch circuit with a 5V supply for the other circuits. The circuit can be used to dim incandescent lamps and dimmable LED lamps.



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