Infrared Beam Break Receiver

Thread Starter

spike1947

Joined Feb 4, 2016
84
Hi

Can anyone help me with the attached schematic , I don't really understand were the line of " VREF" connects to , maybe I can not see the tree's for the forest ! .

cheers

spike
 

Attachments

Thread Starter

spike1947

Joined Feb 4, 2016
84
Hi

Thanks for your reply , I can see in IC1D that 13 and 14 on the IC are fed to 14 ,but were does the output of 14 go to ! ,I still don't understand " VREF " , also is the output of IC1B supposed to be to output 7 , and were doe's COMP go to .

Please excuse me I am just getting into Electronics , maybe I should read a bit ( lot ) more ! .

spike
 

John P

Joined Oct 14, 2008
1,785
This circuit is an AC-coupled system processing the signal from a phototransistor, but it's operating off a single positive supply. IC1D is a buffer amplifier which generates a pseudo-ground at about 40% of the input power supply level. This is then fed to the + terminals of IC1A and IC1B, which allows them to operate both above and below the "reference voltage".
 

Thread Starter

spike1947

Joined Feb 4, 2016
84
Hi again
Do I take it that 14 , 3 and 5 of the IC LM324 are linked together ! , still don't know were COMP goes to .
This circuit is an AC-coupled system processing the signal from a phototransistor, but it's operating off a single positive supply. IC1D is a buffer amplifier which generates a pseudo-ground at about 40% of the input power supply level. This is then fed to the + terminals of IC1A and IC1B, which allows them to operate both above and below the "reference voltage".
Hi
Thanks for that info , got that , the circuit is fed from a 9 Volt battery ! , could you tell me also were do the COMP connections go to .

spike
 

ericgibbs

Joined Jan 29, 2010
9,302
hi spike
COMP goes to D3 driven by the IC1B OPA.
E
NOTE: what Bertus has posted, ref modulated source

EDIT:
Consider the 'pointed' end of a OPA schematic symbol as an Output
 

John P

Joined Oct 14, 2008
1,785
IC1B is a sort-of peak detector which attempts to charge C3 via D3, while the voltage divider formed by R7 and R8 tends to hold a constant voltage there. If the voltage on C3 (the designer calls it COMP) exceeds another reference voltage generated by R9/R10/R11, then the output of IC1C goes high and turns on T2, which sounds a buzzer and lights an LED.

I'd have wanted to add a little one-shot timer which could give a minimum flash/buzz period when the output trips, because it seems to me as if this circuit could give you tiny little signals which would be difficult to detect. Maybe a few more components around IC1C could make the timing function happen.

Edited to say sorry, I had that backward. The output on COMP is normally high, and goes to the negative input of IC1C. Of course as an intrusion detector, the normal state of the system is with the light beam unbroken! You want the output to trigger when there's no light hitting the sensor.
 
Last edited:

Thread Starter

spike1947

Joined Feb 4, 2016
84
IC1B is a sort-of peak detector which attempts to charge C3 via D3, while the voltage divider formed by R7 and R8 tends to hold a constant voltage there. If the voltage on C3 (the designer calls it COMP) exceeds another reference voltage generated by R9/R10/R11, then the output of IC1C goes high and turns on T2, which sounds a buzzer and lights an LED.

I'd have wanted to add a little one-shot timer which could give a minimum flash/buzz period when the output trips, because it seems to me as if this circuit could give you tiny little signals which would be difficult to detect. Maybe a few more components around IC1C could make the timing function happen.
Hi

Thanks for your reply , yes it is only a very short burst to the alarm , I will have to see how I can increase the time ,any idea's ! .

cheers

spike
 

Thread Starter

spike1947

Joined Feb 4, 2016
84
Hi

Thank you all , for all your replies , I have tried to do a schematic that I can understand from the schematic I first put on here , would anyone be able to have the time and patience to check it out ! .

cheers and again thanks , what a great site , and nice people willing to help people like me that are very new to electronics .

spike
 

Attachments

GopherT

Joined Nov 23, 2012
8,012
Hi

Thank you all , for all your replies , I have tried to do a schematic that I can understand from the schematic I first put on here , would anyone be able to have the time and patience to check it out ! .

cheers and again thanks , what a great site , and nice people willing to help people like me that are very new to electronics .

spike
D3 needs to go to the right of D2 in the lower left quadrant of your 324 chip.
 

ian field

Joined Oct 27, 2012
6,539
Hello,

Also the light emitter must be modulated.
A constant light source will not work.

Bertus
History proves you wrong.

But pulsed works a lot better - a filter at the receiver that only passes the pulse frequency, coincidentally also excludes interference from mains lighting.
 

ian field

Joined Oct 27, 2012
6,539
Hello,

@ian field , The receiver schematic has no filtering.
There is an amplifier and a full wave rectifier.
The only filtering may be the coupling capacitors:

View attachment 104206

Bertus
What do you want me to do about it?!

There's designs available on the web - the TS can select one based on the advice given here.

The original break beams used a bulb as the light source - too slow for pulsed.

High speed semiconductors made pulsed operation possible since the invention of LEDs.
 

ericgibbs

Joined Jan 29, 2010
9,302
A DC coupled detector/amplifier is susceptible to the ambient lighting conditions.

Unless he uses a decent collimator tube at the detector, the detector, in bright light will biased in the On state and become useless.
Also if the ambient light level is high there will be sufficient light to keep the detector signal in the 'unbroken' beam condition.

The web is littered with Threads from newbies saying that their DC coupled beam breaks are not working as expected.

You can get around the ambient light problem by using a 'slicer' circuit at the detector end, but it's easier to switch the emitter and use a AC coupled detector system.

E
 

Thread Starter

spike1947

Joined Feb 4, 2016
84
A DC coupled detector/amplifier is susceptible to the ambient lighting conditions.

Unless he uses a decent collimator tube at the detector, the detector, in bright light will biased in the On state and become useless.
Also if the ambient light level is high there will be sufficient light to keep the detector signal in the 'unbroken' beam condition.

The web is littered with Threads from newbies saying that their DC coupled beam breaks are not working as expected.

You can get around the ambient light problem by using a 'slicer' circuit at the detector end, but it's easier to switch the emitter and use a AC coupled detector system.

E
Hi Guys
I am only wanting it to be off any use during the night time really .

cheers

spike
 
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