Innovative Touch-Controlled Dimmer with Memory Functionality
Introducing a cutting-edge touch-controlled dimmer that goes beyond the ordinary, incorporating a unique setting memory feature. This innovative design allows the dimmer to remember the last brightness level set before it was turned off, ensuring seamless continuity in lighting preferences. The core of this project lies in a specialized integrated circuit (IC), the LS7534 from LSI Computer Systems, readily accessible from suppliers like Farnell. This IC is directly powered from the domestic AC powerline, a setup streamlined by the use of capacitor C3, strategically implemented to prevent any undesirable thermal dissipation.
Implementing Intelligent Power Control with Triac and Touch Pads
In this section, we delve into the intricacies of the dimmer’s power switching mechanism. The triac, a pivotal power switching component, is precisely activated at the zero crossing point of the mains. This synchronization information is relayed to the LS7534 through R1 and C2. The triac is then deactivated after a specific segment of the sine wave, enabling fine adjustments to the brightness level. The touch pads interface with the UP and DOWN inputs via high-value series resistors, a configuration crucial for safety. These resistors must not be altered or replaced by a single equivalent resistor for safety reasons. Additionally, the sensitivity of the touch control can be tailored by adjusting the pull-up resistor values, R4 and R5, within the range of 1 MΩ to 4.7 MΩ.
Ensuring Interference Reduction and Safety Measures
Choke L1, designed as a conventional toroidal type, serves the vital purpose of minimizing interference radiated during the triac’s deactivation, in tandem with capacitor C1. For safety compliance, it is imperative that both C1 and C3 are class X2 types, specifically engineered for direct mains operation. Regarding the triac selection, any 400 V, 2–4 A type can be used. However, it is essential to opt for a fairly sensitive type, with a trigger current not exceeding 50 mA, to ensure proper triggering by the LS7534.
Although the circuit diagram indicates a maximum lamp power of 200 watts, higher power ratings are feasible. In such cases, the triac necessitates a heatsink, which adds bulk to the project. If the dimmer is not integrated into an electrical wall box, choosing an insulating case is crucial. This precaution is essential because, in the absence of a transformer, the entire circuit operates at AC line potential, posing a fatal risk upon accidental contact.
User-Friendly Operation with Distinct Touch Patterns
Operating the dimmer is straightforward, contingent upon distinguishing between long and short touches on the touch pads. When the light is off, a brief touch (typically 34–325 ms, as per the datasheet) on UP gradually illuminates the lamp to the previously set maximum brightness. Conversely, when the light is on, a quick touch on DOWN gently dims the lamp until it is extinguished. Engaging in a prolonged touch on UP (typically longer than 334 ms) gradually intensifies the brightness up to its maximum limit, beyond which further adjustments are futile. Similarly, an extended touch on DOWN reduces the brightness to its minimum level.