There aren’t many external sensors required. On the prototype I’m currently working with I’ve added temperature sensors to keep track of both internal and external temperatures. In part so they temperature can be displayed but also, as part of the planned features, giving improved ability to monitor temperatures for the heater control.
The sensors I use are waterproof and can be daisy chained so you can have as many sensors as you like, all connected to a single input pin on the Arduino. Each sensor has a unique address so if you want to have an external sensor and three internal sensors so you can take an average of the internal sensors then you can do so.
Experimental – SMS
In order to allow truly remote control and reporting from the van I have played with an SMS shield. This allows the Arduino to send and receive text messages which, with suitable security, might be used to control the van remotely… turn the heating and lights on, for example, when you start walking back from the pub or get a text alert should someone open a van door when you’re not there. The below are the options I’ve looked at although I’ve yet to evaluate them individually.
Experimental – GPS
This is very much experimental and came out of the thought process that potentially I may have add an SMS ability to the panel, how about I add a GPS so the control panel can text me to let me know where the control panel (and van) is. Primarily this would be a security feature giving you a simple built in tracker.
Experimental – Water level sensors
I have water tanks underslung on my van which is convenient in many ways and a real space saver but it’d be nice to know how much water is left in the fresh water tank and when the waste tank is getting full. I’ve experimented with a number of ways of doing this with mixed success. The coolest way by far was to use ultrasonic sensors. These can measure the distance in mm between the sensor and the surface of the water inside the tank. The problem is that they need a lot of space above the tank but I’m still working on that !