Circuit Description The mains Voltage to supply the control electronics is supplied through it's own fuse (control Fuse) in to the mains indicator switch and then the mains transformer. Power Supply The 12VAC output of the transformer is rectified by the bridge rectifier. But before it is smoothed, it is fed in to base of the zero crossing circuit via R1 and R2. The smoothed DC is separated form the unsmoothed DC by diode D2 The smoothed Dc is regulated by regulator 2 (IC2) to provide a smooth 12v supply for the analogue input socket ( to power remote analogue desks). It is then taken through regulator 1 (IC3) to provided the smooth +5v supply required on the board. Zero Cross the zero cross circuitry consisting of R1, R2, D1,R3 and the BC547 Here the unsmoothed DC is feed in to the BC547 Via the voltage divider, R1 and R2. the transistor is held 'On' until the unsmoothed DC drops below 0.6v. the transistor will stay off till the unsmoothed DC rises above 0.6v when the transistor will once again be held 'On'. R? is used as a pull up and this zero crossing signal is fed in to RB0 interrupt port of the PIC. Analogue Inputs The 6 Analogue Inputs are fed through a resister divider to create the 0 - 5v signal required form the 0- 10v analogue input. The divided analogue signal is then fed through a buffer in to the analogue input of the PIC. The buffer consists of a NPN transistor operating in emitter follower mode. the buffer output then connects to the PIC Input RA0 - RA5 (Note RA4 is not an analogue input) Digital Inputs The DMX512 input is buffered through the 75176 ( Line Driver) and converted from the current loop to a serial signal. this is then routed in to RC7 serial Rx Pin of the PIC. Dill Switches The dill switches are multiplexed out of Pins RC4 - RC6, with their setting sensed by the PIC on pins RC0 - RC3. 7 Seg Display The display is driven serially through a 74HC164 serial to parallel converter. The PIC is connected to the Serial parallel converter through pins RC4, as data and RC5 as clock. Triac Drive The Triac are driven through optical isolators MOC3020. The PIC outputs RB1 - RB4 drive the LED in the isolators via resistors R5 - R8 When the Led is on the Isolators drive the gate of the triac through R9 - R12 causing the triac to trigger on and hopefully switch the light on . R13 - R16 and C6 - C9 are a snubber network to protect the triac. Each individual output channel has it's own fuse placed before the Triac to protect the Triac drive circuit. Also the Whole AC input is Fused and the AC input to the Mains Transformer (Not Shown).