In NHM-7 white leds are used for LCD and keypad illumination. For LCD illumination four leds are used and for keypad six leds.
Current through leds is controlled by transistor circuitry. External transistor driver circuitry is used as constant current source in order to prevent any change in battery voltage be seen as changing led brightness. Battery voltage is changing for example during charging depending on a charger, battery type and age.
LEDs are controlled by the UEM PWM outputs. Both LEDs are controlled by KLight output of the UEM. Current flow through the LEDS is set by biasing the transistor and limiting the current by resistors. Current is set separately to keyboard and LCD leds.
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You can now recondition your old batteries at home and bring them back to 100 percent of their working condition. This guide will enable you to revive All NiCd batteries regardless of brand and battery volt. It will give you the required information on how to re-energize and revive your NiCd batteries through the RVD process, charging method and charging guidelines.