Circuits & Schematics Light - 3

The simple circuit in Figure 1, which can be powered with a 3.6 V nickel-cadmium rechargeable battery, lets you use an LED to detect light. The circuit consumes practically no quiescent power. Two LEDs act as photodiodes to detect and respond to ...

Portable systems often use LEDs of different colors and in varying quantities of each color. Some examples are white for the display backlight, green for keypad illumination, and red for power. Typically, the LEDs derive power from at least two ...

Cities and towns worldwide are considering and installing LED streetlights to help save electric energy, reduce costs, protect the environment, and improve lighting for their citizens. Despite this trend, the lamps’ turn-on/ turn-off time ...

LEDs find wide use as indicators and as light emitters in devices such as optocouplers. In some applications, the LED or the emitter may be located remotely at some distance from the main unit. Typical examples are dashboard-mounted automotive ...

The human eye is remarkably sensitive to changes in light level. In ambient light ranging over several orders of magnitude, the eye can detect changes of only a few percent, yielding an incredible dynamic range. The primary trick is that the ...

I recently needed to control nine seven-segment displays for a microcontroller's serial port. The complication I faced was the need to provide a continuous brightness adjustment for all the digits from completely dark to fully bright. I ...

A popular category of aiming/pointing aids is the reflex, or “red-dot,” sight. This system finds use in such diverse applications as astronomy, archery, and shooting. In the reflex sight, light from an internal source typically a ...

You sometimes need to drive a white LED from one 1.5 V battery. Unfortunately, the forward voltage of a white LED is 3 to 4 V. So, you would need a dc/dc converter to drive the LED from one battery. Using the simple circuit in Figure 1, you can ...

White LEDs find wide use in backlighting color-LCD screens in most portable devices, such as cellular phones, PDAs, and MP3 players. Multiple LEDs often connect in series to ensure that the same current flows through every LED. To forward-bias ...

LED-driver circuits can be dimmed by applying a variable duty cycle (pulse-width modulation, or PWM) to the LED. PWM exploits LED behavior: At higher current levels, the LED’s light output is higher for a given level of power dissipation ...