We’ve recently received a pretty nice challenge: build a very specific tool at an affordable price. The customer, SOLINJECTION, is well known to local insurance companies like AXA and MAAF. Actually, they are the very last line of defense before someone might lose their house due to soil movements.Their technology allows private, public or business owners to continue using their building, even when its foundation has been displaced due to soil movement. Generally this happens during soil moisture changes, like alternating rain/dryness periods, sometimes combined with an initial flaw during the construction phase.The results are pretty terrifying:
As you can see, the entire building has visibly cracked. Not all is lost, especially if no structural damage has occurred. What Solinjection does is to inject a stabilizing resin near the foundation. The resin expands and hardens, rising the building during this process and stabilizing the soil for a very long time. Resin composition, injected volume and injection spots are a highly kept secret.
Alain TABATABAI, CEO of Solinjection, launched us the initial challenge. Industrial solutions for measuring a crack’s evolution exist. The price tag however is very prohibitive (think several thousands). Equipment rental are not that cheap either.
The challenge was simple: build a device that can measure up to 1/100 mm at up to 25mm, easy to install, easy to configure, cables kept to a minimum, capable of relaying the information in real-time to the internet for later analysis and most of all : inexpensive. Like sub-hundred inexpensive. A real challenge for our IoT team.
First of all, we’ve tried the classic solutions: why not use a laser rangefinder. There are some precise ones, even for the hobby market (like this one). The price tag but most of all the accuracy were not sufficient. Another approach was necessary.
A digital caliper has the necessary accuracy and is cheap. Some even expose their data pins, making it very easy to establish an interface an get the measurement values.
A prototype was built using our favorite prototyping framework: .NET Micro Framework. Why favorite? Because it’s the fastest prototyping platform out there, at a marginal higher price. Best of all, it uses C#, a language we’re all familiar at Ai3, Microsoft Partner of the Year in France in 2013.
The only problem with the digital caliper is its size. We don’t need such an extended range (typically 150mm) and most of all it’s too cumbersome to create a small object.
Instead, we’ve decided to use a digital dial indicator. Thanks to mass production, they remain very inexpensive and with a sufficient accuracy over various temperature ranges. Even better, they use almost the same protocol as the digital calipers we’ve used during the first stage of the prototyping.
The final product looks like this:
A watertight container, a ON/OFF button and the dial indicator sticking out. Water resistant and easy to install.
The Real Test
The prototype was ready in time for a real test: a pretty large school that developed cracks almost a year ago. The installation was pretty straightforward. Here are some photos during its real test:
Main Board: Fez Mini
Dial Indicator: Generic, 1/100mm accuracy
Battery: Generic 5V 2500mAh
The test was conclusive: the product works as expected!
A 6-channel version will be developed shortly, allowing multiple simultaneous measurements. Stay tuned to find out more shortly, including a client testimonial by Mr Tabatabai.
If you have an IoT subject, please feel free to contact us.