I have a tankless water heater, which needs a minimum flow to be activated. If you run the cold water too high or flush a toilet, it is easy drop the hot water pressure enough to get below that minumum flow rate. You won’t find out until the cold water arrives a minute later, and then you have to wait another minute for the hot water to get back through the pipes from the tankless.
The controller for the heater is in a closet, and has an LED that lights up whenever it is active. I would like to stick a photocell over the LED, and set up a device that will turn on an LED in the bathroom, and one in the kitchen whenever the tankless is running, and switch off when it is not. Then I can know instantly when I need to adjust the faucets or shower to keep the hot water coming. A wire from the closet to the kitchen would run about 20ft, and a wire to the bathroom would be around 60ft.
I don’t really know anything about electronics, so I am looking for some advice on what kind of devices and design I would need. I’ve been wanting to learn, and thought this might be a good beginner’s project. I would like to start with a basic design or approach, and then learn what I need to understand and implement it.