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Infra-Red Proximity Sensor (II)
Using 40Khz IR receiver IC
By Ibrahim Kamal
Last update: 4/4/08

Overview
This article deals with a more advanced IR proximity sensing scheme, as compared to the one proposed in the previous article. It is also more expensive but provides more accurate results even in sunny outdoor environment.

This sensor is practically not affected by ambient light, and it can provide detections ranges that exceed 1 meter. However, The main idea remains the same where Infra-Red light is emitted on an object, which reflects the light back, then the reflected Infra-Red light is sensed with a special IR sensor. The whole difference is in the way IR is sent and received.


1. The Principle of operation
As I said, the main idea behind obstacle detection using IR is to send Infra-Red (IR) light in a
certain direction, and if an object is present no too far from the sensor, IR will be reflected back and detected by the sensor. But as you may already know, one of the biggest problems that can cause the malfunctioning of an IR proximity sensor, is the ambient light and surrounding sources of IR like the sun and halogen lamps that can cause false triggering of the sensor.

The ingenious solution that was developed to avoid this problem, is to send pulses of IR light at a certain frequency instead of a constant beam, and build a receiver that would only detect IR pulses of the same exact frequency, cutting of all pulses of higher or lower frequency. The kind of device capable of filtering signals this way is called a bandpass filter. There are a lot of types of bandpass filters, a whole branch of electricity is dedicated to this subject. Instead of building a band pass filter, we used a very common IR receiver Module as the one shown in figure 1.A, that incorporates a receiver, an amplifier and a very reliable filter that rejects all the signals that are a couple of kilohertz far from the original central frequency, all in one single integrated circuit, just as big as a 5V regulator. The central frequency is fixed by the constructor usually at 40 khz.

In order to achieve the best possible results, it's important to understand how this IR receiver detect the 40 Khz IR pulses among all other sources of light. This will help you to take some important factors in consideration

Figure 1.A

while designing similar sensors using the same IR receiver.

Figure 1.B shows in simplified way the composition of the IR receiver and the way it filters all the source of light except the the 40Khz IR signal. It all starts by generating the 40 Khz pulses of electricity that are fed to an IR LED, emitting 40Khz pulses of Infra Red light. A weaker signal but with the same frequency is reflected from an eventual obstacle to the IR receiver, it passes through the IR-PASS filter, which will eliminate other sources of light which are not IR (visible light).

At this point the photo diode hiding behind


Figure 1.B
the IR-PASS filter still detects a lot of noise due to other sources of IR light like the sun for example, so the signals received by the diode are fed to another stage composed of an active filter to select the 40Khz IR signals among all others, amplify it and demodulate it, providing a clean logic output (5 or 0 volts).


2. The electronic Circuit
The electronic circuit for this proximity sensor is shown in figure 2.A, as you can see it is composed of two main parts, the sender and the receiver. The sender part is composed of the four NAND gates, the 2N2222A transistor and the IR LEDs. The first two gates are a NAND gates oscillator, they generate the 40 Khz square wave required to send valid signals that are compatible with the receiver IC. The second two gates are configured as one single AND gate, used to enable or disable the sender part. The potentiometer R1 adjust the current injected into the LED thus it controls the strength of the emitted IR beam and thus it controls the range of the proximity sensor. The potentiometer R2 is used to precisely adjust the frequency of the signal that drives the IR LED.

The Receiver is pretty simple, because is basically relies on the U2 the IR receiver is discussed above. The low pass RC filter composed of R6 and C2 is very important to eliminate the noise especially that the emitter and the receiver share the same power supply. Noting that the output of U2 (the IR receiver) is active low, it is clear that the LED D2 will glow when an object is detected by the sensor.


figure 2.A



3. Components positioning
Like in most home made proximity sensors, the sender LEDs and the receiver are placed on different sides of the PCB in such a way that the PCB optically isolates the receiver from the
direct IR emissions of the LEDs. Note that if the IR receiver detect the IR light of the LED directly; before it hits an objects that reflects it back, the whole process of object detection wont work. Figure 3.A shows the path of the beams from the IR LED to the object and finally to the IR receiver.

You can also notice that the PCB is inclined at 35°. Actually the PCB was designed to be mounted this way on a robot or for other application to totally protect the sensor from ambient light. This way, even the sun light with all its infrared radiations don't perturb the operation of the sensor. This is due to the fact that most - if not all - of the strong ambient light sources come from a relatively high position and thus, the light beams of the such sources of light will hit the PCB instead of the receiver. Only the vertical or almost vertical beams will reach the receiver. It is clear that we may be losing a part of the 40 KHz IR beams sent

Figure 3.A
from the IR LED, but we also also eliminating all most probable sources of error. If you want to be sure for 100 % that the reading of the sensor is not affected by ambient lightning conditions, you can still use the "software based ambient light detection" technique explained in this previous article.

A last note on component positioning is the fact that we used two IR LEDs instead of one in the previous sensors. The use of two leds increases the angle of vision of the sensor, but do not increase the range to am important extent. if you want to build a sensor that concentrates on a smaller angle, you can use a single IR LED.

Figure 3.B shows the two IR LEDs while they are being carefully positioned by trial and error to achieve the desired coverage area.


Figure 3.B


4. Conclusion
The technique proposed in this article is sophisticated and reliable enough to be used in mobile robots for obstacle avoidance, for automatic doors, for parking aid devices or for alarm systems, however, the main weakness of IR remains the same, which is the fact that the reflectivity of the IR beams highly depend on the shape, size and color of the object. In other words if you adjust your sensor for detecting objects at a distance of 50 cm, important variation of this distance can be observed between a big white wall and a small black purse on the ground for example.

Techniques that are further more sophisticated have been developed to overcome this point of weakness of IR proximity sensors...



Some picture of the IR proximity sensor.

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Discussion (Last 15 posts preview...)
Preview of the last 15 messages discussing this page. Messages are sorted from the newest to the oldest.
Posted by:
User avatar
ikalogic

on: 03 Sep 2008
Re: Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
I agree with that it is very interesting to be able to detect such long ranges.

Since you are registered to the forum, you will know soon enough by mail when such a project is done and published on the site.

I do have the lazer pointer, but nothing else.. i can't promess when such a project will be ready. :)
Posted by:
s_hatalageri
on: 03 Sep 2008
Re: Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
thanks for the reply....

it would be very helpful if u could do a similar uv or laser proximity sensors and make that as one of the projects on your sites.


it would be really useful as 25 to 30 meters ranges are employed in various application as you know..

looking forward for a positive reply..

thank you
Posted by:
User avatar
ikalogic

on: 03 Sep 2008
Re: Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]

Quoting s_hatalageri: i need a clarification ..

Is it possible to increase the proximity sensor of the above type with detecting ranges upto

30 meters?

if yes ....can u plz show the circuit diagram with the modifications required

and also ..is it possible to make a led glow once the object is detected at ranges in between 25-30 m?


No, i really doubt 30 meters would be doable, at least now that i know of.. i am sorry.

I think you best bet for such ranges is ultra sound.

There may be also some LAZER based range finders that combine lazer, a camera and complex DSP to claculate the distance based on the diameter of the lazer SPOT on a surface...
Posted by:
s_hatalageri
on: 03 Sep 2008
Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
i need a clarification ..

Is it possible to increase the proximity sensor of the above type with detecting ranges upto

30 meters?

if yes ....can u plz show the circuit diagram with the modifications required

and also ..is it possible to make a led glow once the object is detected at ranges in between 25-30 m?
Posted by:
User avatar
ikalogic

on: 13 Aug 2008
Re: Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]

Quoting cassandra: Hi!

Can i use this sensor for the contactless tachometer? if yes, what modifications are to ne made on the c program?


Yes you can use it, and there are no modifications needed to the C code :)
Posted by:
cassandra
on: 13 Aug 2008
Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
Hi!

Can i use this sensor for the contactless tachometer? if yes, what modifications are to ne made on the c program?
Posted by:
User avatar
ikalogic

on: 08 Aug 2008
Re: Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]

Quoting anks_hbk: can i detect an obstacle at 40 to 60 cms away.


sure
Posted by:
anks_hbk
on: 08 Aug 2008
Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
can i detect an obstacle at 40 to 60 cms away.
Posted by:
User avatar
ikalogic

on: 24 Jul 2008
Re: Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]

Quoting girishbe04: Hi

Is there a possibility to measure the speed of a small object (50mmx100mm size), which is just passing in front of the sensor (where the speed could be at around 200 to 500m/sec) using this method? The distance between the sensor and an object is 2m to 3 meter.

If so, anything should I modify from schematic diagram Please suggest


Such a small object is not detectable from 2 or 3 meters, it has to be a few centimeter away from the sensor..

So, Yes, this could be done, without modifications as far as i can imagine.. but as i said, you have to bring the object to zone that is "detectable"...
Posted by:
girishbe04
on: 24 Jul 2008
Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
Hi

Is there a possibility to measure the speed of a small object (50mmx100mm size), which is just passing in front of the sensor (where the speed could be at around 200 to 500m/sec) using this method? The distance between the sensor and an object is 2m to 3 meter.

If so, anything should I modify from schematic diagram Please suggest
Posted by:
kenji83
on: 02 Jul 2008
Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
Hi "saif" , i think you should do some circuit analysing. The 1st 2 NAND gate are becomes a oscillator which generate a pulse signal (40kHz). The function of NAND gate L+L=H,L+H=H,H+L=H,H+H=L. Please keep in mind, the CTRL ,pin2 should always connected to +5V because the signals from pin 8 in pulse form. L+(pin2)=H , H+(pin2)=L



Hope my elpaination would help you ^^ :D
Posted by:
User avatar
ikalogic

on: 13 Jun 2008
Re: Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
Good work aroud!

About the CTRL pin, well, there is no certain frequency for that pin, it is optional anyway, it just allows you to turn on or off the whole sensor. (sometimes, when you have 5 or 6 of those "power consuming" sensors, it interesting to turn on only the onw you're actually reading) :)
Posted by:
one
on: 12 Jun 2008
Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
ok,i've found out wat's the reason dat my IRLEDs r not emitting, just try to reverse bias both D1 and D3, and the whole circuit works fine! So the output for now is,when there's an obstacle existing, my LED at the Rx side will glow. As for the CTRL at pin#2 of 74HC00, may i noe izit required me to connect it to a micro controller and provide some pulses to it?if yes...may i noe wat frequency do i have to apply?
Posted by:
User avatar
ikalogic

on: 12 Jun 2008
Re: Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
why send it my mail, send it over here, you can upload images :)
Posted by:
one
on: 12 Jun 2008
Infra-Red proximity sensors PART 2 (40 Khz Mudulated)
['Quote ]
ok, i will try to send u a screen shot of the circuit i built to ur email, i am following exactly the same circuit design dat u posted it on infrared proximity sensor part2. However, i guess my Tx part is not working properly, there is a voltage across to both IR LEDs, but it doesnt seems to be emitting, cuz my TSOP couldnt detect anything from it.
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