| Introduction | | | | off them and back into the detector. The reflective |
| Infrared sensors are light sensors, which are active | | | | sensor can be used in proximity detection. Some |
| and function in the infrared part of the frequency | | | | vendors provide a built-in sensor that includes the |
| spectrum. They primarily consist of an infrared | | | | receiver and transmitter in a small package. In this |
| emitter and an infrared receiver. They are found in | | | | application note, Avago HDSL-9100 is used in the |
| many object detection applications such as automatic | | | | demonstration circuit. to drive the LED at a higher |
| door openers and burglar alarms, surface feature | | | | current (possibly higher than 100 mA peak). The |
| detection, rotation shaft encoding,and barcode | | | | infrared intensity of the emitter influences the |
| decoding. Some recently used applications in mobile | | | | detection range. Considering the critical requirement |
| devices include auto call-answering, auto | | | | of the PCB size in mobile phone application, the |
| speakerphone activation, and detection of | | | | demonstration circuit uses two GPIO pins to drive |
| flip-in-clamshell phones. This application note is bundled | | | | the LED in parallel and provide current to the emitter. |
| with the firmware and hardware for demonstrating | | | | On the IR receiver side, the desired output voltage |
| interface and analog signal processing of infrared | | | | depends on the detection distance and the value of |
| proximity sensors using PSoC. It alsoexplains infrared | | | | the load resistor (RLOAD). This output voltage signal |
| light sensing and the advantages of using PSoC in this | | | | can be connected to the next stage, such as an |
| solution. | | | | analog amplifier, comparator, or Schmitt-Trigger, to |
| Infrared Proximity Sensor | | | | control various functions. |
| The infrared sensor is made up of the emitter | | | | The selection of the load resistor, RLOAD, plays a |
| (infrared LED) and detector (photodiode). The | | | | significant role in circuit operation. If the RLOAD is |
| emitter emits IR light pulse and the receiver detects | | | | too large, the RC time constant increases, thereby |
| the corresponding light pulse. The sensor is classified | | | | increasing the response time. However, if the RLOAD |
| into transmissive and reflective sensors. As shown in | | | | is too small, it contributes morethermal noise to the |
| Figure 1, in a transmissive sensor, the emitter and the | | | | circuit than higher ones. Therefore, it is important to |
| detector face each other. Objects are detected if | | | | note the current-to-voltage transfer characteristics |
| they interrupt the beam of light between the emitter | | | | for this part of the circuit. According to the |
| and the detector. | | | | applications, the RLOAD can be selected in a range |
| For a reflective sensor, the emitter and the detector | | | | of 50 Kohm to several mega ohms. In this |
| are next to each other, and are separated by a | | | | demonstration circuit, we use a 1 Mohm resistor for |
| barrier. Objects are detected when light is reflected | | | | evaluation. |