astable. Ini adalah kabel seperti yang ditunjukkan pada gambar. Output dari astabil diumpankan ke LED inframerah melalui resistor R4, yang membatasi operasi saat ini. Sirkuit ini menyediakan output frekuensi dari 38 kHz pada 50 persen siklus, yang diperlukan untuk modul detektor / penerima inframerah. Siemens SFH5110-38 adalah pilihan yang jauh lebih baik dari SFH506-38. Siemens SFH5110-38 dihidupkan dengan frekuensi berkelanjutan dari 38 kHz dengan 50 persen siklus, sedangkan SFH506 membutuhkan frekuensi ledakan 38k untuk akal. Oleh karena itu, SFH5110-38 digunakan.
The receiver section comprises an infrared receiver module, a 555 monostable multivibrator, and an LED indicator. Upon reception of infrared signals, 555 timer (mono) turns on and remains on as long as infrared signals are received. When the signals are interrupted, the mono goes off after a few seconds (period=1.1 R7xC6) depending upon the value of R7-C6 combination. Thus if R7=470 kilo-ohms and C6=4.7µF, the mono period will be around 2.5 seconds.
Fig. 2: Proposed arrangement for separation of IR LED and receiver module in the proximity detector
Both the transmitter and the receiver parts can be mounted on a single breadboard or PCB. The infrared receiver must be placed behind the infrared LED to avoid false indication due to infrared leakage. An object moving nearby actually reflects the infrared rays emitted by the infrared LED. The infrared receiver has sensitivity angle (lobe) of 0-60 degrees, hence when the reflected IR ray is sensed, the mono in the receiver part is triggered. The output from the mono may be used in any desired fashion. For example, it can be used to turn on a light when a person comes nearby by energising a relay. The light would automatically turn off after some time as the person moves away and the mono pulse period is over. The sensitivity of the detector depends on current-limiting resistor R4 in series with the infrared LED. Range is approximately 40 cm. For 20-ohm value of R4 the object at 25 cm can be sensed, while for 30-ohm value of R4 the sensing range reduces by 22.5 cm.
