Device to detect low voltage on/off?

I am installing a new little giant condensate pump for my furnace and dehumidifier. There is a NO/NC connection that is normally wired into the red or yellow low voltage line between the furnace and thermostat / it will turn off the furnace in the event that the pump sump doesn’t overflow…

Anyway, any suggestions for something I could wire in and send a signal to my HA instead?

If I understand you correctly Your sump pump over flow is a normally closed switch. This switch is wired into the thermostat line and will interrupt it when the overflow is full. You no longer want it to shut off the furnace just notify you in HA?

If this is the case just disconnect the switch and twist the thermostat line together. In this scenario there should be no power at the sump pump switch. You then use esphome and wire a physical switch. If you search you will find plenty of wiring diagrams.

awesome - it seems like I will want to use ESPHome for this.

After some digging, the pump doesn’t supply any voltage - just allows / disallows current depending on the state. I imagine there is a simple way to interface with the pinout on one of these ESP boards.

pretty excited about this project

You’ll want a nodemcu or a D1 mini for the chip. They’re real generic so no particular brand.

What you could and should do is set this same functionality up in the esp unit. You can connect a relay to the esp chip and attach the thermostat to that. Then separately attach the overflow sensor to the esp.

You can program an automation on the esp chip that will shut the furnace off if the overflow trips. I know this is what it does now but now this can be overridden. However if things ever go down wifi, ha, etc the chip won’t. It will fall back to the standard functionality how the heating system was designed.

Arduino and esp a really similar when it comes to connecting peripherals. Arduino tends to have more readily available guides and how to’s. That said youtube has plenty esp videos. This is a fairly extensive explanation of how esp works. You are going to wire a binary/momentary switch to connect the switch.

I know it may sound complicated but it’s pretty simple. Don’t worry about the automation if you want to go that way. By the time you get things wired you’ll probably be proficient enough to do it yourself otherwise just post when it’s wired up.

Can I clarify your comment about hardwiring in the ESP - Your comment is to have the ESP do the same function hardwired as it would through ha?

This might be a challenge to do everything I intend here but I can give it some more thought.
My intention is to do the following if the sump is full (basically stop each of the devices that create more water):

1.disable AC if cooling is on
2.disable humidifier if heating is on (i can control this through ha & my nest thermostat since it is hardwired)
3.disable dehumidifier on a smart switch

my understanding is that these shutoff safety switches are wired in-line with either the red (stops the furnace from starting) or yellow (stops the AC compressor from starting). But, given I have these 3 devices, and I run with cooling or heating, I want to disable all three but keep the ability to heat my house.

perhaps I could use the following

  1. wire a switch in-line with the ‘yellow’ AC line b/t my thermostat and my furnac
  2. wire a switch in-line with the connection to my humidifier’s solenoid
  3. hook up a relay to the power to the humidifier

I’m suggesting that should everything fail. The system will fallback to how it works right now. That it is not dependent on HA to operate the way it was originally designed.

You can do everything that you listed. Just take it a step at a time. Get a chip, get a relay and wire it up on a bread board. Once it’s running you can connect it to the sump.

There are a lot of those little kits with different sensors. Although they, the ones in the kit, are usually crap. Good to learn with but not for continuous service. Adafruit and digikey typically have quality components when it comes to sensors.

I wonder if you could help me understand - if I flash my ESP with ESPHome will the settings run locally on the ESP?

Yes what you program on the esp with esphome will run locally on the chip. It does not need home assistant to function.