How to design a circuit that control light bulb brightness automatically?

How do we design an electricity circuit that will let (let's say microchip) to control the brightness of light bulb automatically (let's say it goes bright then dim then bright and repeat forever)





If we use ';pot'; or potentiometer, i don't know if there's a kind of that that will work with microchip...How to design a circuit that control light bulb brightness automatically?
There are ';electronic pots';, but they are a kludge and not cheap.





For DC, one method is to connect your microcontroller digital outputs to a d/a converter to get an analog signal. Then, send this to the base [gate] of a transistor. The emitter-collector [source-drain] for bipolar [MOS] transistors forms the variable resistor. The combination of the d/a converter and the transistor effectively form a digital pot. However, it burns a lot of energy.





A smarter way is to use pulse width modulation [PWM]. Some microcontrollers have PWM capabilities built in. The PWM output generates a stream of pulses. The pulse width is varied to dim the light. The frequency can be adjusted to make the load operate properly. PWM is really cool because the transistor is either fully on or off; either way it uses little power, so most of the power is used by the load.





For AC, triacs and thyristors can be used as dimmers. They conduct when turned on, until the voltage crosses zero.How to design a circuit that control light bulb brightness automatically?
Can't you program the microchip to do it? And a pot is just a resistor. it will work with anything.
if we design circuit by parallel combination