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Capacitive Touch Light Dimmer For AC Line Environments

IP.com Disclosure Number: IPCOM000242279D
Publication Date: 2015-Jul-01
Document File: 5 page(s) / 240K

Publishing Venue

The IP.com Prior Art Database

Related People

Atmel Corporation: OWNER

Abstract

A circuit, system and method are disclosed that detect TRIAC current spike (di/dt) events in a capacitive touch light dimmer application to determine times for taking capacitive sensor measurements. The electric field generated by a di/dt event can be detected by a circuit and used with an AC waveform zero crossing event circuit to determine when to take a capacitive sensor measurement. In a first step, “clear” times are determined for capacitive sensor measurements. In some implementations, an average clear time is determined over multiple AC cycles. In a second step, capacitive sensing is performed. This may be averaged over multiple AC cycles and the averaging can be performed by software and/or hardware. Noise countermeasures can also be added in software and/or hardware for extremely adverse conditions. In some implementations, a low cost zero crossing circuit can be used to determine the timing of the AC waveform for relative measurements using, for example, an analog comparator. For di/dt detection, a low cost printed circuit board (PCB) antenna can be used to detect the di/dt event.

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capacitive touch light dimmer for ac line environments

Background

Electronic dimmers for lighting use a triode for alternating current (TRIAC) to block portions of the alternating current (AC) waveform.  The amount of the AC waveform blocked by the TRIAC determines brightness.  When the TRIAC fires, it causes a large change in current or current spike over a small amount of time (di/dt).  The value of di/dt is directly proportional to the strength (voltage) of an electric field it produces.  This electric field can be detected by a capacitive touch sensor and can prevent the capacitive touch light dimmer from operating reliably.   

keywords

Capacitive touch sensor, electronic lighting dimmer, TRIAC, zero crossing detection, AC waveform. 

Summary

 A circuit, system and method are disclosed that detect TRIAC current spike (di/dt) events in a capacitive touch light dimmer application to determine times for taking capacitive sensor measurements.  The electric field generated by a di/dt event can be detected by a circuit and used with an AC waveform zero crossing event circuit to determine when to take a capacitive sensor measurement.  In a first step, “clear” times are determined for capacitive sensor measurements.  In some implementations, an average clear time is determined over multiple AC cycles.  In a second step, capacitive sensing is performed.  This may be averaged over multiple AC cycles and the averaging can be performed by software and/or hardware.  Noise countermeasures can also be added in software and/or hardware for extremely adverse conditions.  In some implementations, a low cost zero crossing circuit can be used to determine the timing of the AC waveform for relative measurements using, for example, an analog comparator.  For di/dt detection, a low cost printed circuit board (PCB) antenna can be used to detect the di/dt event. 

Description

                       

                       

                                                            FIG. 1

           

            FIG. 1 illustrates mapping of di/dt events to an AC waveform.  In this example, we assume an AC waveform with a 16 ms cycle.  The objective is to take capacitive touch measurements at times during the AC cycle when TRIAC noise interference is minimal, i.e., when di/dt events are not occurring.  In some implementations, an average di/dt event time can be determined over multiple AC cycles.

            FIG. 2 is conceptual diagram of an example system 200 for capacitive touch light dimming for AC line environments.  In some implementations, system 200 includes microcontroller 202, capacitive sensor 204, zero crossing circuit 212 and di/dt detector circuit 214.  Microcontroller 202 further includes touch controller 206 and analog comparators 208, 210.  In practice, system 200 would include other c...