What Is the Light Convergent Reflective Sensor on OMRON’s New Sensor Eval Board?February 12, 2020 by Robert Keim
Let’s take a look at the 2JCIE-EV, which comes with sample code and supports a wide variety of sensing applications.
As components shrink and packages become less compatible with hand soldering or even hot-air soldering, engineers are increasingly reliant on evaluation boards.
Well-designed evaluation hardware is particularly helpful with sensor applications: sensors often come in compact form factors, and even when a more soldering-iron-friendly package is available, a professionally designed and assembled board may help us to more accurately assess the sensor’s ability to achieve the desired performance.
The 2JCIE-EV from OMRON comes equipped with a temperature/humidity sensor, an ambient light sensor, a MEMS barometric pressure sensor, a MEMS motion sensor, and a MEMS microphone. It also supports four additional types of sensors that can be connected through an expansion port: a MEMS thermal sensor, a MEMS flow sensor, an air-quality sensor, and finally, a light convergent reflective sensor.
My guess is that many of us were in familiar territory until that last item in the list; what in the world is a light convergent reflective sensor?
Robust Optical Object Detection
Detecting the presence of a solid object is a requirement in many applications. Some examples suggested by OMRON are floor-gap detection in a robotic vacuum cleaner, paper detection in a copy machine, and cup detection in a coffee maker.
It’s natural for us to consider an optical approach to these electronic tasks—i.e., why not shine some light and look for a reflection, since that’s basically a (highly) simplified version of how human beings usually “detect” things such as coffee cups and printer paper.
Well, this certainly can work, but there are some complications. One prominent issue is the relationship between the color or transparency of an object and how much light is reflected. The detection signal generated by a black object or a transparent object may be much weaker than the signal generated by a white object at the same distance, leading to potentially unreliable detection performance.
The situation becomes more complex when objects to be detected are in front of a light-colored background. The intensity of the reflection created by the background may be comparable to the intensity of the reflection created by a dark-colored object, and consequently, it may be quite difficult for the system to recognize the presence of darker objects.
Diagram of how a light convergent reflective sensor works. Screenshot (modified) used courtesy of OMRON
OMRON proposes its light convergent reflective sensor as a solution to these limitations.
I don’t fully understand the principle of operation here, but the general idea is that lenses spread the emitted light and focus the reflected light in such a way as to create a specific detection zone. Objects beyond this zone are not detected, and objects within the zone are somehow detected more reliably, regardless of color or transparency.
Evaluating Sensors Using Common Processor Boards
In addition to supporting a wide range of sensor types, the 2JCIE-EV facilitates evaluation work by providing direct compatibility with hardware that many engineers and students already have and know how to use.
The board comes in three versions. One is intended for use with MKR Arduino products and plugs in as a “shield”; one is for Raspberry Pi and is therefore considered a “HAT”; and the third is a “FeatherWing,” since it is intended for use with Adafruit’s Feather platform.
One thing to keep in mind with this evaluation board is that you may need to make some hardware modifications. By default, the 2JCIE-EV is configured to receive power from the processor board, so if you want to use an external power supply, you need to remove the zero-ohm resistor from location JP1 and install it in location JP2 (see page 8 in the datasheet for more information).
JP2 and JP1 on 2JCIE-EV. Image (modified) used courtesy of OMRON
I recently wrote a component-centered technical brief on a proximity sensor that uses infrared signaling. I’d be interested to hear your thoughts on whether OMRON’s light convergent sensor offers significant advantages relative to an infrared solution.