I built an ESP8266 device to monitor a few things on my little sailboat, which sends me an hourly status email and an emergency email should something out of the order be noted.
I’d like to move all this to Home Assistant via ESPHome. I need to measure the voltage on two 12 volt batteries, the temperature and humidity using a DHT and note a single binary input.
My thought is to start from scratch, likely with an ESP32, but am at a loss as to how to proceed.
Help ?
Places to start could be here and here.
I’d recommend an esp32. You can look at some recommendations here.
How does your sailboat currently communicate? Wifi etc?
Yes, Wifi. In fact, it simply sends emails, once per hour (to let me know it’s still alive) and anytime something “unusual” is noticed. Unusual would be the temperature being too cold, the 110 VAC power going out, a 12 volt battery voltage being low or a bilge pump turning on. While not much of a programmer, I figured out how to do this using the Arduino IDE. But this doesn’t give me realtime monitoring nor historical information, both of which could be very very useful. And doing this through HA would also cut down on the amount of SPAM I send myself.
Could you describe the sailboat set-up a little more? It’s not obvious to me;)
I assume it is an actual boat rather than like a toy?
Are you saying it has a wifi router on it?
I assume you don’t have a dedicated HA server on it (raspberry pi etc?). Is there a HA server set up in another remote location on another wifi network?
Mainly just trying to confirm what existing power, connectivity/communication it has.
If you’ve already got an ESP sending emails then probably you’ve got enough existing networking and comms for an ESPHome project, but looking to confirm details.
If your HA server and ESPHome node are on different WiFi networks, then threads like this may be helpful to figure out communication options.
Thanks for the reply and forgive me the delay in responding; Christmas and New Years got in the way. 
To answer your questions
Yes, it’s a real boat, a 28 foot sloop.
An access point is on the dock, about 20 feet away. That’s how the existing device sends me emails. The access point is connected to my home network via a LONG “ethernet cable”. (Actually, the “cable” is a pair of TP-Link Powerline Ethernet adaptors that work fantastically well.)
An HA server is part of my home network with many devices, including a number of ESPHome devices, part of HA.
I know enough to add an ESPHome device using a DS1820 one wire temperature sensor. It’s the multiple device configuration, and especially the scaling for the 12 volt battery monitor, that I’m unclear on.
Alan
Right so your network is all set-up and you don’t need to do anything tricky I think? That’s good.
Well these should be pretty straight forward and there should be plenty of examples around (I assume the binary sensor is on a gpio?). If you have any specificv issues maybe share whatever you have so far for an ESPHome configuration and we can take it from there).
For the 12V battery, I’m not so sure. Possibly a voltage divider and an ADC sensor (x 2). A bit like this.
There’s a bit for scaling buried in this one: