I have a device running at 12vdc that has a pair of terminals that can be opened and closed for the device to operate. I understand how to use an optocoupler to open and close the terminals, however the twist here is that I need the terminals to be normally closed (ie to be connected most of the time), and opened when the opto is activated (eg by an MCU). This is preferred to keeping the opto activated due to wear (?) and the failure state.
The below was offered here when I asked about normally closed optocouplers, but I'm having trouble understanding how to integrate it, most likely because I don't fully understand how it works.
- What is the input to R4? Any available voltage? Where would I get that from? One of the terminals?
- I also don't have a "load" as such - I just want to complete a circuit. Is that load implied (eg behind the terminals), or should I add a resistor?
- Are there any other solutions to this? Although I see the value in an isolated solution, I'm interested in hearing in other ways to solve the problem. I also have regular mechanical relays which have NC terminals for instance.