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The triac is a current driven device; it will switch on (i.e. T1, T2) whenever enough current is driving its gate. The required amount of gate current can be determined through triacs datasheet; there are two types (according to gate drive) low gate current triacs and a standard gate current triacs. To switch a triac with MCU you can use I/O lines directly whoever you may need to use as parallel line as needed to proved the required current to drive triac (according to gate drive by data sheet).
If you are going to use this triac to switch main’s operated equipment then care should be taken to avoid shock or the use of an opto-coupler as an insulator is a must.
Care must also be taken to type of load connected to triac; inductive load (i.e. AC Motors) may require a snubber circuit.
Use Optically isolated triac driver like MOC3022. The LED inside MOC3022 will be driven by 89C51. This driver will depend upon AC voltage in your country.
MOC301X - For 110V AC RMS
MOC302X - For 230V AC RMS
See datasheet (Fairchild is good) of this driver for exact shematic or let me know if you can't find it.
1) Your circuit will be isolated from high-voltage side.
2) Sufficient gate drive will be supplied to the TRIAC to turn it on fully.
In case you dont want to use it make sure your microcontroller is able to suuply enough gate current to the TRIAC. And make sure you don't touch any of the parts while the circuit is active.
To turn-on the TRIAC you need to make uC's pin high (which is connected to gate) and vice-versa.
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