[ WARNING - HIGH VOLTAGE ] 
[ DANGER OF SHOCK / DEATH / PROPERTY DAMAGE / FIRE / POWER LOSS / UNEXPECTED BEHAVIOR ]

 -- for experienced professionals only --
--- USING THIS DESIGN/CIRCUIT/SCHEMATICS/COMPONENTS YOU AGREE THAT YOU'RE FULLY RESPONSIBLE FOR ANY AND ALL PROBLEMS OR ERRORS CAUSED BY THE DESIGN/CIRCUIT/SCHEMATICS ---

BT138 based AC 220V dimmer with external Zero-Cross for microcontroller (MCU) to be used with special pulse width modulation (PWM) with a proper time base and zero reading. 

The input from microcontroller is completely* isolated from the mains circuit. With this circuit it should be possible to control the power of the output devices connected from 0% to 100% very similar to PWM, which includes but is not limited to: light bulbs and low inductance AC single phase electro-motors. 

Avoid higher load output devices or NEON lamps. 
Higher load AC motors tend to need pre-calculated LC filters around the Triac or else they don't work in phase with the input of the AC line or don't work at all. Also the Triac can overheat!