Call bells, designed to draw attention, are commonly used in various environments such as offices, hospitals and residential care homes. Here, we explore a simple 12V LED dimmer circuit, incorporating an LM556 dual timer IC, which also functions as a call bell. The LM556 dual timer IC houses two 555 timers within a single 14-pin package. In this LM556 PWM-based LED dimmer circuit, the brightness of the LEDs is effortlessly controlled using a potentiometer. The author’s prototype is shown in Fig. 1.
Circuit and working
The circuit diagram of the LED strip dimmer and call bell, as shown in Fig. 2, is built around a 230V AC primary to 15V, 500mA secondary transformer (X1), a bridge rectifier (BR1), a 12V voltage regulator (LM7812, IC1), a dual timer (LM556, IC2), a MOSFET (IRFZ44, T1), a transistor (BC337, T2), an 8-ohm 0.5-watt speaker (LS1), and a few other components.
The 230V AC mains voltage is stepped down to 15V through stepdown transformer X1. This 15V secondary output of X1 is fed to bridge rectifier BR1. Capacitor C1 filters the voltage ripples, and the filtered output is supplied to the voltage regulator LM7812 (IC1). IC1 provides a 12V regulated DC output to power IC2. LED1 serves as a power-on indicator. Both timers of the dual timer LM556 (IC2A and IC2B) are configured in an astable multivibrator mode.
LED strip dimmer
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