The Led dimmer circuit you see in the diagram works like a DC dimmer, the brightness of a number of Led groups can be increased or decreased. The power supply of the circuit is + 12V and the Led groups are grouped in series and in parallel so as not to exceed the power supply of the circuit. The circuit can be powered from a battery or directly. SW2 is the on/off switch of the circuit. Switch SW1 is the switch that keeps the LEDs in continuous transmission.
Here the diode D112 (1n4148) has the task to disconnect the signal output of the timer 555 from the circuit supply, because the timer 555 works when the switch Sw1 is off. The function of diode D111 (1n4148) is to protect the output of the timer. The timer U1 555 is the main controller, which makes the circuit work as a dimmer.
The materials RV1, R1, R2, C1 and C2 are essential for the proper functioning of a timer. When the position of the potentiometer RV1 is changed, the brightness of the LEDs changes as the frequency at the output of the timer changes.