In another thread in the Caravan section on this forum relating to Water Meters I made a brief reference to a method some caravan parks use to determine the contents of remote storage tanks. There have been a few private inquiries which I will address here rather than answer individually.
There is the general case of a farmer who establishes a small resort on a remote section of his land. Being off the beaten track it does not have an electricity supply. The ablution facility has a water tank, filled by a solar pump, and two solar water heaters, one for the showers, and one for the scullery.
Since there is a reliance on an energy source that is not entirely predictable, there is potential for anxiety over whether there is sufficient water being supplied to the tank, and whether the water to be heated is hot enough to satisfy the guests. Since the resort is some distance from the farm’s admin area it is not convenient to repeatedly go there and back to physically check the status.
Our solution is this:
A controlling device, the master node (MotherNode), is connected to the establishment’s wireless LAN which is centred on a standard internet router, as found in any home. This device is made from a Raspberry Pi Zero (the only version of Pi that is in plentiful supply), which host a Node-Red control flow. We generally supply a basic workflow framework that is then user-customised to suit the particular requirement. Some skill is required for this but it’s something anybody can manage given a bit of perseverance.
We supply a slave node (SplitNode Base), connected to the same LAN, that feeds data to the master node and receives commands in return. The slave node has an LCD display attached (C-Node) that shows all current system parameters.
The slave node communicates with its distant brother by low-power FM radio. At the remote end of the radio link is the slave node’s brother (SplitNode Remote) that receives input from the sensors at the ablution facility, and sets outputs in accordance with commands from the master node. The sensors include an ultrasonic scanner (or a load cell that can weight things), two heat probes, and 2 switch inputs.
The SplitNode Remote, (which is powered by its own solar panel, charge controller, and 7Ah battery), can read the height of the water level in the tank using the U/S scanner, the temperature inside the storage of both water heaters by using the heat probes, and two opto-isolated switch inputs. These switches can monitor the state of door or gates, or anything that comes to mind. It also has two relays with a 10A switch rating that are under command of the master node.
Although the relay outputs are available to do the master node’s bidding, it is usual to control the pump by a float switch in the top of the tank, which starts the pump when there is even a slight drop in water level. This makes the relay outputs available for some other purpose, if needed.
The radio link, depending on local conditions can be up to 5Km long if directional antennas are used. The signal strengths at both ends of the radio link are continuously reported to the master node.
To disseminate this data over a wider area the master node continuously updates a repository on the establishment’s web domain (as determined by the user), from where it can be reproduced on any device connected to the Internet, using the device’s Internet browser – no special app is required. So the farmer can be running errands in town and simultaneously be aware of the state of his resort.
Unlike some other IoT systems this does not delegate control over ones resources to some far away cloud data centre in China, or who knows where. Everything stays in-house and under own control.