Hey everyone. I know this is a wall of text but I put my actual question at the bottom and this first part is just to help understand what level of electronics I'm at and my background understanding of this circuit. I could be wrong about some of it. If so, please correct me. I'm relatively new to electronics but I'm studying for an associates in electronics technology at a local tech school and they really skimped over Transistors and Thyristors so I've purchased a bunch of books and have been playing catch up over Christmas break. All of this information below is still somewhat new to me as I've learned it over the past week or so through teaching myself.
Right now I'm in the process of trying to understand how I can use a TRIAC to switch on an off AC line voltage for lightbulbs, household appliances, etc. I've come across a circuit that has really answered that question for me at this website: http://computerchristmas.com/christmas/link-how_to/HowToId-7/LowLimit-0
Here is where the ULN2803 comes in. I get that it uses TTL to switch its outputs on (at least I think thats right) and if I'm not mistaken that means it uses a +5V Pulse or Square-Wave to switch them on. In doing so it turns on the Optoisolated TRIAC (used to isolate the AC line voltage from the rest of the circuit) which triggers the gate of another TRIAC which actually switches on the AC to whatever load you have connected.
I pulled up the datasheet for the ULN2803 because I wanted to understand how a +5V pulse on its input could switch on the Optoisolated TRIAC. In the following image I added in RED example pins for how I understand it to be connected. I don't know if they are right or not.
My actual question: I'm not sure how the circuit on the right actually works. I believe the triangle is an Invert or a NOT gate but I haven't taken digital electronics yet just read about it on my own. Can someone please help me understand how the circuit on the right operates so that when you have a +5V input it switches on the output and what the purpose of Example Pin 18 and Pin 10 is. Thanks!
Right now I'm in the process of trying to understand how I can use a TRIAC to switch on an off AC line voltage for lightbulbs, household appliances, etc. I've come across a circuit that has really answered that question for me at this website: http://computerchristmas.com/christmas/link-how_to/HowToId-7/LowLimit-0
Here is where the ULN2803 comes in. I get that it uses TTL to switch its outputs on (at least I think thats right) and if I'm not mistaken that means it uses a +5V Pulse or Square-Wave to switch them on. In doing so it turns on the Optoisolated TRIAC (used to isolate the AC line voltage from the rest of the circuit) which triggers the gate of another TRIAC which actually switches on the AC to whatever load you have connected.
I pulled up the datasheet for the ULN2803 because I wanted to understand how a +5V pulse on its input could switch on the Optoisolated TRIAC. In the following image I added in RED example pins for how I understand it to be connected. I don't know if they are right or not.
My actual question: I'm not sure how the circuit on the right actually works. I believe the triangle is an Invert or a NOT gate but I haven't taken digital electronics yet just read about it on my own. Can someone please help me understand how the circuit on the right operates so that when you have a +5V input it switches on the output and what the purpose of Example Pin 18 and Pin 10 is. Thanks!