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Designing distance measuring sensor with IC555 and 565, IR LED and photodiodes

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John_Correa

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Is it possible to make a distance measuring sensor using IC 555 and IC 565 along with an IR LED and photodiode pair? I have the transmitter circuit which pulses the IR LED at a particular frequency using IC 555(used in astable mode). Now I want to design the receiver circuit using photodiode and IC 565(PLL) in order to filter out the ambient light as it has the ability to recive only a particular frequency and lock itself to it. But I'm not able to put it right. I plan to give the analog output of 565 to an ADC and then process it using a microcontroller. Please help.
 

Re: Distance measurement

well you can use TSOP
 

Re: Distance measurement

Guys is it not at all possible to use IC565 for distance measurement? Please reply. My college project is hanging because of it.
 

Re: Distance measurement

You can do it with ultrasound, setting the PLL in 40Khz and ultrasonic transducers. But, with infrared led, it is not possible.
 

Re: Distance measurement

penrico said:
You can do it with ultrasound, setting the PLL in 40Khz and ultrasonic transducers. But, with infrared led, it is not possible.
Click to expand...
Why it's impossible to measure distance with IR? If it's possible to do with ultrasound, could you tell us some more about the method and the apparatus?

Cheers,
-Kender
 

Re: Distance measurement

kender said:
penrico said:
You can do it with ultrasound, setting the PLL in 40Khz and ultrasonic transducers. But, with infrared led, it is not possible.
Click to expand...
Why it's impossible to measure distance with IR? If it's possible to do with ultrasound, could you tell us some more about the method and the apparatus?

Cheers,
-Kender
Click to expand...

Because the speed of the light is = 299,792,458 m/s (1,079,252,848.8 km/h), and the speed of the sound is 344 m/s (1230 km/h).

So, if you want to measure the distance to an object at 10 m, the time to take to the light to go and return will be aproximately 67 nano-sec (10-9), and to the sound it take 60 mili-sec(10-3).

It's not imposible, but... Could you do an circuit as faster?

Regards.
 

Re: Distance measurement

kepi19 said:
Because the speed of the light is = 299,792,458 m/s (1,079,252,848.8 km/h), and the speed of the sound is 344 m/s (1230 km/h).

So, if you want to measure the distance to an object at 10 m, the time to take to the light to go and return will be aproximately 67 nano-sec (10-9), and to the sound it take 60 mili-sec(10-3).

It's not imposible, but... Could you do an circuit as faster?
Click to expand...

Laser rangefinders (LIDARS) do work somehow. I don’t think they measure time of flight of an impulse. There should be a more clever method that doesn’t require nanosecond time measurements. For example, you can modulate the light with some relatively low frequency and measure the phase of the reflected signal. I suspect that John (the original poster) had this method in mind.
 

Re: Distance measurement

kender said:
Laser rangefinders (LIDARS) do work somehow. I don’t think they measure time of flight of an impulse. There should be a more clever method that doesn’t require nanosecond time measurements. For example, you can modulate the light with some relatively low frequency and measure the phase of the reflected signal. I suspect that John (the original poster) had this method in mind.
Click to expand...

Ok, I understand you.

But I think that the implementation isn't as simple as ultrasound.

Regards.
 

Re: Distance measurement

I've thought of a new prototype of doing the same. As discussed, the time of flight of light is not measurable (atleast not easily). But the amplitude of reflected light can be measured. So if I use an IR LED to transmit the light and a photodiode receives the reflected light, then by using a current to voltage convertor, the distance can be measured with fair accuracy(proportional to photodiode current), I suppose.
But this idea has a small glitch. IR LEDs are enormously affected by ambient light mainly sunlight but even tubelights and bulbs take their toll (to the order of 0.1V) on it. I've tested this under various circumstances like in the evening, in dark rooms, with tubelights, bulbs and in bright sunlight. The last case gives the worst output as the values go haywire. So now I'm planning to use a bandpass filter to filter out the ambient light. At the same time, the IR LED will be pulsed using IC 555 at a frequency which will be passed through the BPF. The choice of frequency will be in the range of 10kHz -80kHz as almost all digital TSOPs are available in that range. I think this is the range where sunlight causes minimum interference. I'm working on this prototype now.
Anybody having any suggestion for the same, please let me know.
Thanks.
 

Re: Distance measurement

The intensity of reflected light will depend on the nature, texture/finish and the colour of the reflecting object. How will you account for that?
 

Re: Distance measurement

Hi Rajesh. The surface of reflection is white at all times. This is guaranteed. So any way out now?
 

Distance measurement

The angle of the surface should be constant too.

A standard way of getting rid of ambient light is to modulate the LED with some frequency and high-pass filter the signal after the photodiode. I would choose a frequency from 1kHz up. For example, IR remote controls use 38kHz.
 

Re: Distance measurement

Hey even I am working on the same lines ! can you guys please tell me exactly how to go about making the filter circuit ?
Even the surface which I am working is white and flat at all times !
 

Re: Distance measurement

prodigyaj said:
Hey even I am working on the same lines ! can you guys please tell me exactly how to go about making the filter circuit ?
Click to expand...

In a simple case, just about any high-pass filter topology will work. Even a 1-pole RC high-pass filter will work. Just pick your filter cutoff frequency well above 60Hz. And pick the carrier frequency (with which you modulate the IR LED) well above the filter cutoff frequency.
 

Re: Distance measurement

Can you please explain the necessity for using cutoff frequency over 60Hz?
 

Re: Distance measurement

John_Correa said:
Can you please explain the necessity for using cutoff frequency over 60Hz?
Click to expand...
To cut the ambient from fluorescent lights. Fluorescent lamps produce light, whose intensuty is a sine wave with the same frequency as mains AC (60Hz in US, 50Hz in Europe). We don't see the fluorescents blink, because 60Hz frequency is too fast our eyes to track. Photodiodes will see a 60Hz, though.
 

Re: Distance measurement

and what about camera flash lights ? I hear they have a very high frequency ? so even camera lights can cause problems right ? and what is the solution ?
 

Re: Distance measurement

If the surface and angle of incident light is same, you may proceed but keep in mind that the light variation (decay) is NOT 'directly' proportional to the distance but has a logrithmic function.
 

Re: Distance measurement

rajeshbij said:
If the surface and angle of incident light is same, you may proceed but keep in mind that the light variation (decay) is NOT 'directly' proportional to the distance but has a logrithmic function.
Click to expand...
Why is is logarithmic? My personal guess would be - 1/quadratic.
 

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