Re: How do touch control lamps work

In the kind of touch control lamp I'm thinking of, a person can turn the light on or off, or even bump the brightness up or down a notch, simply by touching a metal part of the lamp. I'll attempt to answer by explaining concepts without explaining implemention details.

The light is controlled by some electronics at whose heart is a tuned circuit that oscillates at a particular frequency. The tuned circuit includes the lamp's metal parts. When a person touches the lamp's metal, the electrical characteristics of the tuned circuit are affected (technically, the capacitance changes), either changing the frequency of oscillation or causing it to cease entirely. Additional circuits sense this change and translate this to signals that cause an electronic switch to turn current to the light bulb on or off, or just partially on; in fact, the very same type of electronic switch is used here as that which is used in manually controlled dimmer switches.

So how does touching the metal change the tuned circuit? Here's a simple mechanical analogy: Suppose we had a tuning fork, and we repeatedly bang on it with a small hammer to keep it vibrating. A person in the next room with good hearing and excellent sense of musical pitch listens through a keyhole to the sound made by the tuning fork. When this listener hears the tuning fork change pitch or stop, the listener changes the position of the light switch on the wall from off to on, or on to off, or bright to dim, etc. Now suppose that someone comes along and attaches some weights to the ends of the tuning fork, or actually grabs hold of the vibrating forks. The pitch of the fork will change, or it will stop vibrating entirely. The listener in the next room hears this difference and throws the switch to a new position.

Think of the tuning fork as the lamp controller's tuned circuit, and the person's hand affecting the tuned circuit in the same it affects the tuning fork. The listener in the next room is actually the sensing circuits monitoring the tuning circuit for changes.

Steve Czarnecki