Varying bulb luminosity using ATMEGA16

We know that on the market there are plenty of devices that replace normal wall switches and let you adjust the luminosity of a bulb. But if you want to make an `intelligent` home or a more complicated device to adjust the power of a light bulb whatpossibilitiesdo you have 1. If you are using DC, than it`s simple: just use a switching element (
Varying bulb luminosity using ATMEGA16 - schematic

a BJT or a MOSFET ). You just apply PWM (Pulse Width Modulation) and vary the duty cycle from 0% to 99% and you can adjust the luminosity of a lightbulb or LED or you can set the speed of a motor. If I would use a BJT to implement my application, I would have to consider that in the reverse active region thebehavior isdifferent from theforwardactive region. Because the application will be used at 50Hz(lowfrequency) to "drive" a light bulb (small load), and the maximum necessary current that will pass through it will be under 4 - 5 Amps, I have chosen to use a TRIAC. The same application can be easily modified(add some diodes) and can be used to drive high power loads(motors, heating elements, etc) using Thyristors. 1. The galvanic separation is used for safety. The transformer takes the 230V AC from the mains and gives on the output a voltage between 8 to 24V(which is safe tot touch). 2. Use the voltage from the secondary winding of the transformer to power up the uC, and also to detect de 0 crossings of the mains. To power up the uC we need DC, so we take the AC from the transformer and afterrectifying(which include a bridge rectifier and a capacitor for filtering) block we obtain DC voltage 3. The uC uses 5V. We take the DC obtained at 2, use it as an input for the 7805 integrated circuit. At the output of the 7805 we will obtain 5Vstabilized. We will use this voltage to power up the uC. 4. Zero crossing detector - it`s...

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