Seeing as there seem to people on here that know about everything….

I want to measure the voltage of a 12v battery and ambient temperature and have an alert sent to my phone, either by SMS, Email or notification, when it goes out of a preset range.

I have WiFi available to connect to.

Is there anything off the shelf that will do this? I don’t really want to go down the road of setting up a Rasberry Pi etc and want it to be fit & forget, not have to tweak it every time a developer updates something.

I can buy something off the shelf for £200+ but I’m looking for a much cheaper option.

Cheers

An esp32 will do it with less fiddling than a pi, but it’s still a project. Eg https://randomnerdtutorials.com/esp32-ds18b20-temperature-arduino-ide/ Once set up it should just run

A colleague has done this on his boat using a Pi with an SMS module plugged in. He wrote the code himself to alert him when the shore line goes down etc.

I suspect the £200 off the shelf option is the best zero effort option.

A friend of mine is into classic cars, and apparently there is a problem in that world whereby swapping out your gearbox (e.g.) throws the speedo out because the speedo is a simple thing designed for a specific diff ratio.

You can buy an off the shelf box that uses a GPS to determine speed and drives a motor to make the speedo turn, thereby removing the drivetrain from the picture. Such a box costs £400.

We decided to have a go at making one ourselves, since it should be possible to do it much more cheaply.

So far, yes, the hardware cost is absolutely cheaper. But we’re thousands into development costs 😂

If you fancy making one yourself as a project I think you could easily do it with an Arduino plus a module to do the GSM bit (for SMS) or WiFi (for email). There will be a bit of hardware work required to step the 12v down to something the Arduino can safely read. Similarly there will be a bit of software work to do the battery level reading and send the SMS or email. Bit more work all around if you want it to be low power (e.g. if it’s running off the 12v battery it’s monitoring).

However, if that all sounds totally foreign and not something you fancy getting into, the £200 off-the-shelf solution is the way to go IMO.

I don’t really want to go down the road of setting up a Rasberry Pi etc and want it to be fit & forget, not have to tweak it every time a developer updates something.

this is a job for a micocontroller such as Arduino/ESP not a Pi as it’s such a simple task, plus Arduino has analog inputs whereas Pi doesn’t without additional hardware. It would be fit and forget, once working you’d never have to update it. Loads of project examples if you Google.

However, a simpler option… I’ve been getting right into home automation lately, my main weapon of choice is the Shelly WiFi relay. The software is great, they’re incredibly versatile and really simple to wire up & configure.

You will want a Shelly 1 relay which can be powered by 240 AC or 12V DC. There is an add-on (called the Shelly Addon!) which literally just plugs into the back of it. This will give you 3.3V, a digital inout and an analog input. You can then just connect the same voltage sensor module that you’d use with an Arduino to the analog input (and also your battery). This one looks ideal: https://uk.farnell.com/dfrobot/dfr0051/analogue-voltage-divider-v2-arduino/dp/3517888?gclid=EAIaIQobChMIg4nMiKmR7wIVyMLVCh0G-AMLEAQYBCABEgJk6fD_BwE&gross_price=true&mckv=sUtuiKIF1_dc%7Cpcrid%7C459864482156%7Cplid%7C%7Ckword%7C%7Cmatch%7C%7Cslid%7C%7Cproduct%7C3517888%7Cpgrid%7C114464710024%7Cptaid%7Cpla-531854587592%7C&CMP=KNC-GUK-SHOPPING-SMEC-Whoops-Newstructure-31Aug2020-Desktop-Hi

You can then monitor the voltage from an app and/or set the relay to perform an action automatically if it drops to a certain level. You also have the actual relay itself, which you could use for another task or even something like disconnect the battery automatically if the voltage drops (if that’s useful?) They have their own phone App and (free) cloud service for sending notifications etc.

cost is £19 for the WiFi really + add-on, £3.50 for the sensor so way cheaper and probably more customisable than the off-the-shelf, no soldering or programming – just plugging wires in and configuring via a web interface. You can get a waterproof junction box for under £4 from Screwfix to use as a project box to house it all if necessary.

If you go down this route and need any help just give me a shout. (Just watch out that there’s a jumper that needs to be set if you’re using DC rather than AC to power the thing, it’s in the manual but judging by the number of posts on the FB group who have fried one a lot of people don’t read it 🤣). I’m probably making it sound complicated but these things are actually REALLY simple to use.

EDIT: just seen the bit about temp as well, you’d need a 2nd relay + add-on to measure that as each add-on only has one analog channel, alternatively they do an off-the-shelf WiFi temp/humidity sensor that’s about £26.

I’d say £200 for WiFi, voltage and temperature and alarm function is a good price.

You can get cheaper versions around £30 if all you want is to manually check battery voltage via Bluetooth.

If you want much cheaper then I think then Arduino route is better than a Pi as you want to do analogue sensing and interfacing. You can get Arduino modules with built in WiFi and GSM so they can text or email you a warning when required.

Cheers all. Just revisiting this to update.

Someone has very kindly built me a little box of tricks that monitors temperature and 2 battery levels for the price of the parts (<£25) and it’s winging its way over to me.

I don’t understand how it works but it sends a message when out of set limits and can also request its status on demand. Fits the bill perfectly 🙂

@phil5556 Nice. FWIW out of interest I tested my Shelly idea. They have an even more suitable product (Shelly Uni, £12) which I’d forgotten about despite having a couple in my spares box 🤣 Designed to retrofit to existing devices to make them WiFi/smart, it has a built-in ADC up to 36v so you don’t even need anything else to monitor battery voltage, just a cheap temp sensor and then a waterproof junction box from screwfix etc to house it. Total cost under £15. Can send a push notification to your phone via their cloud service (which I’ve not use before and tbh found a bit klunky but it does work!) and you can also use the app to lo in remotely to monitor the sensors. It also gives you 2 digital outputs in case you want to trigger anything remotely.

@zilog
interested .. anything 2 way so I can trigger a relay?
I haven’t done stuff like this for decades and trying to catch up… any learning would be good

Currently got the diesel heater with a radio remote and made 2 water heaters that runs off it…
However at the moment one water heater (2 120mm CPU coolers) is manually connected which is a right faff and then the pump is started when the outlet temp reaches a limit and switched off via a second thermistor relay when the water temp reaches 40C. It’s a bit too efficient as the outlet is cooled to <5C above ambient so does sod all to heat the van while I’m waiting for the water.

The other (pre-heat/free energy) runs off the exhaust through an old EGR valve but takes 20+ mins to heat from 5-40C so not ideal if you need a shower after a ride. Not fitted yet as it involves drilling extra holes in the chassis.

Ideally I’d be able to switch on combo’s before I got back to the van.. and also run a couple of 12v HVAC air diverters .. one to the water heater and the other to the clothes/boot drier (and switch on the extractor from the clothes drier) less useful as usually I want to run the clothes drier AFTER but I get bugged when stuff is inconsistent.

@zilog that does look a good solution cheers, one for the future if I ever decide I need any thing else like this.

@stevextc yes it’s all 2-way, assuming you’ve got something in your van to give it WiFi/internet connectivity as that’s how these products work! The product I mentioned doesn’t have a relay itself but it has 2 outputs that could be connected to relays. The company makes other products though which do have built-in relays which are pretty neat.

A mate is building a campervan at the moment and I was trying to persuade him to have a Raspberry Pi running Home Assistant as the “brain” to control & automate everything 😀. It’s a fair old learning curve if you haven’t used it before though, taken me months to figure out what it can do (everything, basically!) and what the best ways are to do those things. But ultimately it allows you to properly automate things, so in your example, you wouldn’t need to send a signal that you were on your way back to your van, it would figure it out itself by tracking you & fire up the heaters etc itself!

@phil5556 yeah, I’m a big fan of hacking stuff together myself but home-automation is so popular at the moment, there’s loads of off-the-shelf products available now that didn’t exist even a few years ago, plus most of the exciting stuff is happening at the enthusiast end of the market so loads of the most useful kit is actually low-cost/open source!

Looks interesting … I do like stuff like that to be consistent.

I guess I can use a DC-DC step up since most of the stuff seems to start at 24v and for reasons of my liking stuff to be consistent everything is 12v based. (Incl mains hook-up that gets stepped down straight to 12V DC)

yeah consistency is good, one of the good points with the Shelly stuff though is it’s very versatile! (Uni runs off 12-36V DC or 12-24V AC and most of the relays can use 12V DC, 30-50V DC or 240V AC)

most of the relays can use 12V DC, 30-50V DC or 240V AC

Ah, might need to look more. The ones I was looking at were 24-60VDC or 220-240AC.

yeah consistency is good

Well it is for me.. I’d rather have a common standard and some compromises than lots of different standards. It bugs me just having the 2 separate thermistor relays … even though I need 2 sensors… (one for air and another for water) but it just niggles at me with “there must be a neater way”

Ah, might need to look more. The ones I was looking at were 24-60VDC or 220-240AC.

probably the Shelly 2.5? Has 2 built-in relays, nifty bit of kit, I used one to replace a borked roller-shutter control unit, cheaper plus makes it smart in the process! The bog-standard Shelly 1 can run off 12V though.

So…. I was looking at the Unify and Google also popped up with a door sensor.

Which got me thinking, I often forget to close the garage door. Could I use it to show whether the door is shut & warn me when it opens?

And how does a “potential free” output work to trigger a relay?

Could I use it to show whether the door is shut & warn me when it opens?

yes, but as I’m discovering with home automation, there are many ways to skin a cat, all with pros/cons. If you can get power to it (and wifi reaches!) then the Uni is a decent option, you can wire in any binary digital sensor e.g. magnetic contact switch or microswitch. There ARE battery WiFi options (Shelly make one) but all poor apparently due to the way battery wifi devices need to go to sleep to preserve power. Zigbee (same RF protocol as Philips hue) are apparently a decent battery option, but then you also need a hub.

And how does a “potential free” output work to trigger a relay?

this just means (I think) that the output isn’t electrically connected to the input. In essence it’s just a switch, some kind of solid state relay maybe? So e.g. if you’re powering it with 12V DC, the output can switch 5V DC or low-voltage AC. It’s only 100mA though, so you can’t use it to drive a load… the main usage is to retro-fit older devices to make them smart, so you could e.g. wire it in parallel with the Go button on your coffee machine so you can operate it remotely! You could of course also use it to switch a beefier mechanical relay which could power a load.

If a relay is what you want then some of the other Shelly devices (Shelly 1, 2.5 etc) have relays built in, the Shelly 1 has a 16A relay so useful for driving powerful stuff.

Could I use it to show whether the door is shut & warn me when it opens?

Neos just started doing door sensors for this sort of thing…

https://shop.neos.co.uk/products/neos-smart-motion-kit

We use their webcams, very nifty bits of kit.