Touchpad Indicator LED
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
This article describes a circuit arrangement and method utilizing a light-emitting diode (LED) for indicating low battery power and circuit self-test in a touchpad unit. A single LED (yellow) is positioned behind the front lens of the touchpad. Low battery is determined by the low battery sense circuit illustrated in the block diagram in Fig. 1. A voltage potential is presented to the analog-to-digital (A/D) converter so the microcomputer can determine if battery power is low enough to start blinking the LED. When the battery voltage from the cells gets below approximately 4.5 volts, the LED blinks at a one-second rate, indicating to the user that the batteries need replacement. Infrared transmission stops when the low battery threshold is reached, signalling to the user to observe the LED indicator.