Construction metal imager

-May 15, 2014


Presenting one of the runners-up in the TI LDC1000 inductive sensor design contest.

My design proposal is to use the LDC1000 to build a metal sensing imager for home and office construction. My first idea was switching an array of coils and controlling an indicating LED for each. The cost of even an eight-by-eight array was prohibitive, and would not give a satisfying image.  The second idea was to use a solenoid to activate a marker which would travel through the coil center and mark the surface wherever metal was detected. Again, cost would be prohibitive, and while satisfactory on a construction site, a homeowner might object to having their walls marked up.

Finally, I hit upon the idea of using a smart phone to record and display the imaged metal. I built a prototype application for my Android phone, and produced the accompanying video. The main hardware challenge was the removal of D1, the green SMD LED, and connecting a high output LED in its place. The loops you see are for mechanical strain relief. Additionally, I needed to have the LED on the center-line of the sensing coil, but positioned so the readings are minimally affected.

The hardware being resolved, I began the software development. One would think that a green LED would be seen by a camera as green. I found however that the center of the LED was seen as white. Perhaps the camera sensor was saturated. Adjustments were made in the software and I found the results to be quite satisfying, as shown in the accompanying video.

The screen is split in two, the left side showing the imaged metal as black marks on the white background, and the right side showing the live display. As the device is swept over the metal, the LED turns on. This light captured by the camera is recorded on the left display. Thus, an image of the metal is formed. For the purposes of this demonstration, I used the provided coil. However deeper structures may be sensed with a larger diameter coil.

The interesting thing about this technique is that it can be extended to any number of different sensing applications. Software reuse at its best!

Sensing Design Challenge 2013 winners:

Also see


Loading comments...

Write a Comment

To comment please Log In