project: proximity infrared sensor with 3 modes of operation, for Bolt 18F2550 system.



In a previous project, an infrared remote control was described, based on the circuit TMF5360 or TSOP1736,which integrates a photodiode, as well as a demodulator for 36 Khz signals. This control was implemented with a standard RC-5 remote control handset and operates up to a distance of 10 meters.


In this project, using the same TMF5360 infrared receiver and an infrared diode, a proximity sensor circuit was designed. The circuit connects to the LCD port in Bolt 18F2550 system and permits to detects objets from distances up to 50 cms.

The principle of operation is to generate, by means of the firmware in the microcontroller, a continuous stream of 30 pulses modulating a 36 khz carrier, each pulse with a duration of 835 us, and followed by a space of same duration, as shown in the image below. To generate such signal, the PWM (Pulse Wide Modulation) function contained in the 18F2550 microcontroller is used.

This signal is emitted by the infrared diode TN153BF, reflected by the near objet and detected by the infrared receiver TMF5360. The 36 khz demodulated signal is analyzed by an algorithm in the firmware of the 18F2550 microcontroller, which subsequently activates the relay, when detecting a valid signal.

The proximity sensor may detect the signal reflected by the objet up to a distance of 50 cms, and operates in 3 modes, configured by the microswitches SW1..SW4 of the Bolt board.

Complete MPLAB-IDE firmware files:






The proximity sensor circuit connects to the LCD port of 14 pin of the Bolt 18F2550 board. The infrared diode is covered with a piece of termofit to concentrate the energy of the signal in one direction.

The value of the 1.5 kohm R1 resistor may be modified in a range of 1 kohm to 2.2 kohm to increase or decrease the transmitting power of the infrared diode.

However, too much power to the infrared signal may derive in an unstable behavior of the circuit, given that the IR emitted signal may be reflected by walls or distant objects and reach the TMF5360, triggering the relay even in the absence of a near object.



By means of the 4 dip switches (blue module in the Bolt board)SW1..SW4, the user may program the following 3 modes of operation:

Mode 1 PROXIMITY DETECTOR MODE (SW1..SW4 OFF): relay is active when an object nears a distance of 30 cm or less of the infrared LED. Remains active until the object moves away.

Mode 2 TOGGLE SWITCH MODE (SW1=ON, remaining OFF): Activates relay if the object is near. Deactivates if the object is near again and so on.

Mode 3 TIMER MODE (SW1=ON, SW2=ON, remaining OFF): activates the relay for 6 seconds when the object is near.



The circuit will function with more accuracy with an external wall transformer connected to the Bolt board, due to the on board 5 volt regulator. Average distance of the object to the infrared sensor to trigger the relay will be about 40- 50 cms.

It is also possible to feed the board from the USB cable of the computer. In this case the distance of the objet to the infrared sensor for detection will be about 25-35 cms.

A lamp was connected to the relay terminals to make testing.




During testing, you will obtain different results depending on the object nearing the infrared sensor. The larger the object you will get more power of signal reflected, so the needed distance for detection will be larger.

Also, a white or pale objet will reflect the infrared signal with more efficiency than a dark object.

With a white sheet of paper reflecting the infrared signal, you may obtain distances aproaching 60 to 80 cms.