Moisture & Flood Sensor

This is project started out with the need to build a voice announcements and warnings.

It morphed into a more generic sensor that could be used in a wide range of applications. This is one of the projects where we have worked with a friend to design and build a smart home component in larger volumes. This approach allows us to undertake more smart home projects and complete them more quickly. Producing sensors like this in larger volumes also reduces the unit cost.

Requirements

We had some requirements in mind when we started this project:

  • The sensor needed to be a generic wired sensor, so that it could work with our optically isolated input board.
  • This means it needed to work with a 12V dc power supply but ideally would work with a wide range of voltages.
  • The sensor must use very little power. This is a requirement we have for all elements of our smart home.
  • The sensor needs to use an ac signal on the moisture sensing probes, so that there is no galvanic action and erosion of the probes. This means it can be used in water level sensing applications where the probes are often submersed in water.
  • The sensors must be easy to interface to various devices, so that it can be used with wireless technology if need be.

Design

To complete this project, I have been working with a friend. The circuit design will be described here shortly but, we have constructed a prototype and tested it. The circuit uses an ac signal to connect to stainless-steel probes. This approach eliminates electrolysis problems and erosion issues at the cathode or anode. It is designed to operate from 5V dc to 12V dc and easily interface to a wide range of probes and devices.

Optically isolated input board
For this rain sensor application the moisture sensor PCB will be interfaced to our Home Control System (HCS) using our generic optically isolated input board.

Prototype

Having designed a suitable circuit, we built a working prototype using Veroboard and standard components. This validated that the design worked.

Production PCB

moisture sensor PCB
We had 10 PCBs professionally manufactured by Ragworm, so that we can use them in a number of different smart home applications. The PCB design uses surface mount components to keep it as small as possible (30mm × 40mm).

Circuit and PCB design by Stephen Searby.

Five PCBs made up

Testing

Applications

Networked Wormery

We are using this board connected to a Fibaro Universal Sensor (Z-Wave) in our networked wormery project.

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