Electronic Design
3D Touchless Infrared Proximity and Motion Sensor Kit

3D Touchless Infrared Proximity and Motion Sensor Kit

Take a Si1120 Ir-LED sensor and seven infrared LEDs. Add in one ultra-low power C8051F930 MCU. Mix thouroughly. The result is Silicon Labs' $199 Si1120 Evaluation Kit. It could also be your next 3D gesture sensing system.

No need for heavy duty image sensors or heavy computational hardware for this application. That might have been the route taken when the boss asks for a system to detect hand gestures. True, a video-based system could be more flexible and more accurate for some applications but it is also much more costly and complex. Don't forget to include a lighting system as well because that is critical to the success of this approach.

One the other hand, literally, if the general movement and position of a hand or finger is what is required then check out the Si1120 Evaluation Kit . That is what I did.

The Si1120 Evaluation Kit actually consists of two boards (Fig. 1). One is a standard development board (C8051F930-TB) from Silicon Labs the holds an 8051-based C8051F930 microcontroller. The board has a connector that connects to the L-shaped sensor board (Si11s0 EVB) that has the Si1120 Ir-LED and other LEDs. The latter can have visual references added to it (Fig. 2). The microcontroller handles the sensors as well as the gesture sensing. This can be as simple as detected a logical button press to more complex hand or finger movements. The kit turned out to be a handy way to test out the software and it can be the basis for a target system. The QuickSense Studio software made the task relatively easy.

Reflectance-based Proximity Detection

The key to the system is the Si1120 chip. The Si1120 chips contain an infrared LED and a matching sensor (Fig. 3). The chip has optical windows the protect the sensors and filter out unwanted light. The infrared light is reflected off an object and detected by the sensor. By itself, the Si1120 can be used as a proximity sensor although it has distance but not directional capabilities.

Additional LEDs are added to provide the 3D sensor support. Each LED is individually controlled and placed in an L-shape with the Si1120 near the vertex (Fig 4). The combination of the LED sequencing, including the Si1120's LED, and sensing via the Si1120 allows the software to determine not only distance from the sensor but also position.

QuickSense Studio

QuickSense is Silicon Labs name for the technology being employed by the Si1120 and other chips in the same family. It includes run time libraries, software evaluation tools like the QuickSense Studio as well as analysis tools (Fig. 5). Entire applications can run on an 8-bit micro (Fig. 6) or it can be a front-end to other devices.

Set up is very simple. I downloaded the Windows-based software from the Silicon Labs website and installed it. The USB-based interface was then plugged in.

The next step was to play with the hardware using the QuickSense studio. This includes a number of canned configurations that provide graphical feedback. It is handy to see how the system responds at the low level as well as how thresholds effect performance.

Moving past this is a bit more of a challenge and I didn't take it that far given my current time constraints. Sample applications and a detailed API are provided along with development tools available on the website. In general, a sophisticated customized application could be put together in a couple days.

The system is very neat. It can handle things such as a switch movement like flipping a toggle switch easily. The software can handle a range of simple interfaces very easily such as slider bars or rotator disks or dials. I found the reponse to be very quick. Check it out for yourself. The cost is a bit more than some of Silicon Labs low cost kits but the Si1120 Evaluation Kit is definitely worth the money.
 

 

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