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Author Topic: short range ir  (Read 2773 times)

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short range ir
« on: December 10, 2012, 07:17:56 AM »
Circuit reference: IR Short Distance Beam Cut Detector

Dear sir;
i m doing my final year project, in which i m using eight(8) IR Receiver & one transmitter. All 8 receivers are in sequence. Which out put produces (+5) logic on when it detect IR transmitter LED and vice vesa.
The o/p of all receiver circuit is connected my micro controller port that make a 8 bit pattern. The IR Transmitter Led move one by one on each IR Receiver Led, consequently i m getting a particular 8 bit binary value, and this logic I am using in my project.
This is receiver circuit that I have used .pin 6 is out put and directly connected with microcontroller

My problem is that when I m using single IR Transmitter receiver it is working well .But when I a using 8 receiver circuit on single pcb board with single 5 volt supply there is a problem. And moving ir recever led one by one on each receiver ckt some rec ckt working some one not wrking (what I hv found voltage at inverting pin of 741 not going below 3.26(ref volt at non inverting pin 2).after measurement what I have found-----------------
For single ir transmitter-receiver,
Ref voltage (at pin 3 of IC1 741) =3.26v   
Input at at pin 2 (after filtering and amplifying) =3.6 v (above ref. voltage) when IR LED OFF
Receiver IR Led output (at pin 6) = 1.56 v (LED2 OFF)

Ref voltage (at pin 3 of IC1 741) =3.26 volt   
Input at at pin 2 (after filtering and amplifying) =3.17 volt(below ref.) when IR LED ON
Receiver IR Led output (at pin 6) >=3.56 volt (LED2 ON)

But when I m using 8 receiver circuit (as given above) not working properly .some one circuit working
And giving out put (3.56v) and some one not working.
What I have found after measurement---
Ref voltage (at pin 3 of IC1 741) =3.26v   
Input at at pin 2 (after filtering and amplifying) =3.6 v (above ref. voltage) when IR LED ON
Receiver IR Led output (at pin 6) = 1.56 v (LED2 OFF)

When ir led on , input at pin no 2 of 741 not going below 2.26 (ref voltage at pin 3 which is 3.26). means comparator circuit working fine .
I m unable to find fault where is problem is it in power supply , or op-amp or transistor not amplifying . I have struggling since one week.
« Last Edit: December 10, 2012, 08:45:33 AM by kam »


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Re: short range ir
« Reply #1 on: December 10, 2012, 08:50:35 AM »
You mention that you use multiple receivers but just one transmitter. This circuit uses a method that is reliable only for short distances. First make sure that the distance between the receiver led and the transmitter is less than 15mm.
If that is ok, then measure the voltage of the defective circuits at the junction C1-R3-R4-R5. It must increase when IR is on so that the base of T1 goes above 0.5V. If NOT increase, then the problem is the IR receiver LED probably or the capacitor C1. In that case, remove the capacitor and measure between the LED and R1 - The voltage must increase with IR ON.
Otherwise, the problem is definitely the transistor T1 (or some of the resistors r2-r5-r6)


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Re: short range ir
« Reply #2 on: December 11, 2012, 08:52:48 AM »
thanks for reply;
                           My distance is fine. what i observe that...
voltage changes at node (means connecting point at LED1 ,R1 and C1) in fallowing manner.
                            ~0.01 volt              when Transmitter  LED OFF.
                              1.71 volt               when Transmitter  LED ON.
there is no changes at connecting point of C1, R3,R4 and R5 .it is about 0.88 volt and it is constant there is no effect of Transmitter LED whatever it is ON or OFF .
is these observations are fine ?

my circuit is fine and working in fallowing way....
OUTPUT at pin 6 of 741 =1.41 volt ....................when transmitter OFF
OUTPUT at pin 6 of 741 >3.00 volt ....................when transmitter ON

my problem is out put voltage is 1.41 volt in off condition . it is undefined region for my microcontroller   means it not comes in LOGIC ZERO region. i want to reduce it below 0.8 volt.
for this i have used two zener in series but it is and then voltage reduced to 0.82 volt,but this is in single receiver circuit. But when I m using eight receiver circuit and using two diode in series it is giving at some out 1.0 volt and some where 0.99volt and some where it is 0.88 volt out of eight IR Receiver circuit. Which is not suitable for my microcontroller? So for this I have used LM324 which which gives out Put 0.0volt when transmitter OFF.
I have used 2 LM324 Ic for my eight receiver circuit. And now it is working fine.
What I m acing new problem I will discus shortly. I think it is so long reply
…but i have alot of thing from these experiments.