Need to improve my ir distance sensor - Page 1
Forum section: electronics / general

author: momo26
author_rank: Newbie
timestamp: April 06, 2012, 11:33:17 pm
content: Hello,i'm trying to make an infrared distance sensor for a project so i find a simple CKT on the attachement but it need some improvmenti want to integrate with it a high pass filter to avoid noise for ex to let only 40khz frequency to pass but i'm not familiar with filter so i need your helpand this ckt detecte only for 1 - 7 cm if you can improve it to get higher distance like 10 or 15 cm it will be betterso if you have any sugestion thank you for replaying backand sorry for my bad english

author: Rerouter
author_rank: Super Contributor
timestamp: April 07, 2012, 12:57:50 am
content: some minor improvements you can start with, swap out the photodiode with an ir phototransistor, the circuit works by the intensity of the light decreasing by squares, e.g. distance of 1 equals an intensity of one, a distance of 2 is 1/4th of the original, and a distance of 3 is 1/9th,and i assume that the non linear nature of a phototransistor helps balance that, but for longer distances e.g. 1+m you would need the gain of a phototransistor, and for even greater ditances a photo diode darlingron pair,if you just wanted the quick and easy fix, add a second led in parrellel, double the amount of light means double the distance the existing design can read,

author: momo26
author_rank: Newbie
timestamp: April 07, 2012, 01:09:55 am
content: hithank you for your answeryes it will be better if i use a phototransistor,i need to add a filter to avoide dc ir coming from the sun and i'm not familiar with filter so it you have any advise ?and i don't need a large distance 2-15cm will be great for my project

author: Rerouter
author_rank: Super Contributor
timestamp: April 07, 2012, 02:08:01 am
content: filtering dc? the sun is a constantly burning source of ir, you cant exactly filter it, this is why more advanced ir distance meters are pulsed, by measuring the difference between ambient and what is added it knows almost exactly what is being added by the led, however while not that hard to implement, gets tedious, (switching mosfets on an op amp input and all that jazz)but if instead you want to better smooth fluctuations, increase the capacitance on the photodiode / phototransistor, you have an R what you use to zero it, and you have your c, from there you work out your time constant and you have a basic filter, yes it would vary as you zeroed it, but it what its purpose is,

author: SeanB
author_rank: Super Contributor
timestamp: April 07, 2012, 10:42:10 am
content: Most of these use a IR transmitter driven with a narrow pulse of around 100mA but with a duty cycle of around 10%, to keep the power dissipation within the limits of the diode. The receiver is easiest to do with an integrated unit used in a TV or other remote controlled circuit, as these have the IR filter, photodiode and 38kHz demodulator built in. Drive the IR LED with 38kHz and the output will be a logic level from the receiver, which just needs a 5V supply to work. High when IR is received, and low when the beam is blocked. The app notes will give a more detailed description of the supply and decoupling nedded in the receive side, and the transmit side can be a simple 555 timer driving the LED via a resistor. That will need a decoupling capacitor of around 470uF directly across the supply pins to keep supply noise down.

author: momo26
author_rank: Newbie
timestamp: April 07, 2012, 12:48:40 pm
content: hello, and thankx for you're answersyes, i tried before with the photodiode used in TV, but this one send only a pulse when it receeves the signal coming from the irled , and me i need the variation (some thing like this one in the video)so i need juste to implement a simple filter to allow only the needed frequency to passand try to get a large distance by adding another irled like Rerouter sugested to me

author: momo26
author_rank: Newbie
timestamp: April 07, 2012, 07:24:16 pm
content: Hello, i have improved my CKT using some ex found on internetthe ckt is in the attached filei used the frequency generator to simulate because i didn't find the irled lolwell i used the amplitude like the intensity that the photodiode detecteand the frequency as the frequency that will detecte so i will pulse my irdiod with this frequencyi think that the result is prety good , i didn't test it on lab i will do it tomorow and i poste back the resulti used in the simulation an intensity of 5vif you have any advise please feed back

author: momo26
author_rank: Newbie
timestamp: April 09, 2012, 09:14:17 pm
content: hello,i have tested the ckt and it worked well with a frequancy of 200hz, and all the ir comingfromthe sun don't affecte the outputit detecte a distance of 10cm but i have tested it with a phototransistor of 3mm , i will buy anonther one to have more range