Musings about optical (IR) sensor based key switches

Circuit design from Tech Resources

Optical sensor on switch is not a new concept and certainly there are optical sensor based key switches that has been around for quite a while as well.  However, with dominance of spring centric keyboard switches such as buckling spring design or the entire Cherry MX line and its clones, optical keyboard switches are rare birds indeed.  On the other hand, analog switches are now coming back in fashion as the new bleeding edge in gaming sphere.  It is no coincide that mechanical switches are popular these days.  The simplicity, reliability, manufacturing ease and cost are factors that contribute to this.  Adding optical sensors and emitters put more complexity.  However, the benefits are starting to make a good case for an optical based switch.

Mechanical switches are, well, mechanical based.  When two separate metal pieces come in contact, an electrical connection is made and thus generating a signal.  Optical switch depends on an emitter, which is often the case, an infrared light source and a sensor.  When an object obstructs the light path or changes the reflectivity depending on the design, then the sensor knows that a key is pressed.  Now, some clever engineers already realized that if the object that is obstructing the light path is a gradient, then the sensor can capture a diminishing light emission as a function of distance.  Add some computing power, the senor can also calculate velocity and so on.  An optical based system might generate a clear on/off signal as well since physical connectivity is not always a sure and entirely consistent thing.  Because the sensor is entirely optical, the physical interaction of the key switch can entirely be up to the designer’s imagination.  Therefore, it is possible to design some complicated interactive switch that does not depend on any mechanical contact to trigger the switch.

For strictly typing keyboard, these added complexities have little benefit since typing just need to know if a key is pressed or not.  However, as a gaming device or navigational system for say a VR or AR device, then the possibility use cases make much more sense.  Thus, there is a sudden interest in these switches.  Perhaps sometimes later this year, we will see a mass marketed optical sensor based keyboard.  There are already a few prototypes and Kick Starters efforts floating around.  Let’s see what innovations these folks can bring to the table.