SI1143-Based Distance Sensors


We have some affection for the SI1143 chip. We used it for our pulse sensor in which it performs admirably.  Plus we successfully puzzled our way through its  78 page datasheet. So we figured that we would spin up some sensors based on what the chip was supposed to do (i.e. what the manufacturers of the chip thought  it might be good for), namely proximity sensors.

Our summer intern Gavin Atkinson took the lead in designing these two versions or an SI1143 based proximity sensor. They are both exactly the same schematic and parts and only the form factor varies. However the geometry of the LED / sensing chip layout affects the sensor so sensing distances and sensing angles vary a bit.

Silicon Labs wrote an app with  code for “swipe-sensing” that demonstrates detection of swiping your hand over the sensor from different directions. We thought it would fun to see how the sensor might work as a 3D mouse. For you math and code heads, the code that we used in the video uses vector addition to add the three vectors whose inputs are the values returned by the various LED readings and whose angles are represented by the angles between the chip and respective LEDs (0, 120, & 240 degrees). This yielded a vector and direction that was a fairly good decoding of the LEDs into a vector direction and strength as you can see in the video. Summing all three LED values yields a good idea of object distance to the chip – so it would be possible to map these coordinates into 3D space, which we did not do in an explicit way in the video.

SI114 Distance Sensor from gavin atkinson on Vimeo.

The pictures above, and in our video are our prototypes and the assembly technique on the sensors lacks something in the neatness department. In particular we need to find the correct adhesive and technique to glue on the chip’s laser cut “shield”, which prevents LED light from “short circuiting” to the sensor. We also used some diffusers over the LEDs in the video. We believe that wider LED angles will work as well as the diffusers. We also revised the layout a bit as found that the large capacitor was blocking the LED in some situations. Yeah for prototypes working the way they are supposed to!

Some possible uses for the sensor we thought about were:

  • interactive controllers or scroll wheels as in the video link below
  • smart distance sensor for robots so that they might be able to tell heading toward a wall or other object
  • short distance replacements for Sharp IR distance sensors with no “close-in deadspot” that sometimes making the Sharp sensors tricky to apply.
  • touchless 2D or 3D mouse, perhaps hot-cold control for a sink mixing valve, meat packing factory, hospital or surgery suite where hands were either dirty or clean and touchless sensing was desirable.
  • interactive art projects

Distance/Proximity Sensors are in the shop here!

By Paul Badger on August 15, 2013.