Infrared Emitter and Decoder


One encounters infrared (IR) emitter/detector circuits in daily life. For example, there are doors that automatically swing open when a person walks closeby or passes a gate. In essence they operate as follows: The emitter passes an infrared beam which is detected by a phototransistor. When a person walks by, he "breaks" the beam. Upon this event, the phototransistor no longer can detect infrared light and another event is triggered - namely the door opens. Such a circuit is described here. This circuit can be easily made within a couple of hours. One can use simple point to point soldering or wirewrap. Because, of the versatility of this circuit and its small size factor, I created printed circuit board (PCB) artwork. The artwork measures approximately 2 inches by 2 inches. Typical copper boards at stores or surplus are large enough so that one can quickly made 4 of these IR boards at the same time.

One quick note about PCBs. I never had good success with iron-on transfer methods. I thus used the rub-on transfers from Radio Shack. I also imagine you can use the resist-ink pen too, since the trace lines are not thick and component spacing is not critical.

My motivation is to use such a circuit for motor speed detection. The photos that follow show the applicability of this circuit for such purposes. This article is broken down as follows: