Design a 12V LED Dimmer Circuit and Call Bell Circuit

This dual-function circuit operates by converting 230V AC mains power down to a safer low-voltage direct current, which then supplies both an LED dimming stage and a call bell signaling stage. AC mains voltage connects to the primary side of a 230V to 15V transformer (X1). The resulting secondary voltage is processed by a 1A bridge rectifier (BR1) and smoothed by a 1000µF electrolytic capacitor to create a rough DC bus. An LM7812 voltage regulator (IC1) stabilizes this into a clean 12V rail that powers the rest of the board. The core processing unit is an LM556 dual timer IC (IC2), which integrates two independent 555-style timers in a single package. One timer section is configured to generate a pulse-width modulation (PWM) signal. This high-frequency square wave drives the gate of an IRFZ44 N-channel power MOSFET (T1), which rapidly switches the ground path for the connected 12V LED strip to control its brightness efficiently without wasting excessive energy as heat. The second timer section on the LM556 can be utilized alongside components like the push-to-on switch (S1), 1N4148 signal diodes (D1, D2), and a BC337 NPN transistor (T2) to drive an 8-ohm 0.5-watt speaker (LS1) for audible call bell or signaling tones. Various ceramic capacitors (0.01µF, 0.1µF) are distributed across the power rails for high-frequency decoupling and timing stability.