Hello, I am having problems providing a gate signal to turn on the SCR. The transistor AND gate seems to be okay. I have attached the cct I am using. Thanks.
Use a 220 ohm resistor to connect the gate lead between the two transistors, ground the Kathode, expect conduction when the upper transistor is on and the lower transistor is off.
I am trying to trigger the SCR gate when both transistors are switched on. One op-amp is set to output at 0 degrees Celcuis, the other is to o/p when rain is detected. The combined o/p (AND) is to gate an SCR circuit.
To create an AND gate you need to put a resistor between the 12volt supply and the collector of the upper transistor, start around 10k. The upper collector than gives you a NAND output. Adding one more transistor resistor pair will invert the output to a logical AND. For this pair feed the NAND output into the base of the next transistor and the point t between the collector and resistor will be the AND output.
As #12 suggests, add a resistor between the output and the gate of the SCR and connect the SCR as instructed.