As per the image, an operation for manual & Auto logic where manual can overwritten auto command and vice versa. The red circled area is an SCR(Silicon Controlled Rectifier). I'm looking for a SCR which can conduct at ZERO Gate Voltage(Vgt=0) i.e when the Mechanical switch is turned 'ON' the SCR turns 'ON' and it starts conducting 230V AC and when Gate Voltage is provided to the SCR,it turn 'OFF' the SCR and hence turns 'OFF' the load lamp.
I can't use a 'RELAY' or a 'TRANSISTOR' as the current flow in the circuit should be unidirectional.Also in case of 'RELAY' space constraint is an issue.
But either way if I can't find any SCR which conducts at 'Zero' Gate Voltage(Vgt) won't mind using transistor.
Any suggestion for an SCR which can conduct at 'ZERO' Gate voltage as mentioned in above explanation shown in below circuit.
As soon as the mechanical switch is closed micro controller gets the signal through the opto-coupler that the 'Load Lamp' is operated from then mechanical switch also the SCR above the 'Load Lamp' starts conducting for 'Zero' Gate Voltage now if one wants to switch off 'Load Lamp' from remote location it can be done through micro controller which triggers Gate Voltage to SCR. Similarly if one wants to turn 'ON or OFF' the 'Load Lamp' from the remote Location it can be done by triggering SCR located on left. Opto-coupler connected after the 'Load Lamp' is for feedback from the 'Load Lamp' to the micro controller.
Hence for the logic mentioned above one need an SCR connected between the mechanical switch and 'Load lamp' which can be operated at 'Zero' gate voltage
An Opto Coupler which can operate for 230V AC directly.
Part No of both Opto Coupler which can operate at 230V AC and SCR which can conduct at 'Zero' Gate Voltage?