OPB702 Optoelectronics Reflective switch Application - Electronic Circuits Projects Diagrams Free

mesamune80 · 22nd April 2008, 08:38 AM

Hi All,

Anyone of you all come across this device?

http://www.optekinc.com/pdf/opb702.pdf

And anyone can provide the simple connection diagram for this device?

Thanks.

dknguyen · 22nd April 2008, 08:43 AM

The datsheet gives you the internal schematic- a photodiode with a photodetector. Wire up the photodiode with a current limiting resistor the same way you would wire up an LED, and simply wire up the photodetector as an open collector (with a pull-up resistor if you want to measure analog rather than digital).

mesamune80 · 22nd April 2008, 08:59 AM

thanks for the information given,but if i would like to give on /off signal to my pic micro controller which i need 5v for high logic how could i achieve that?
Thanks.

dknguyen · 22nd April 2008, 09:02 AM

You have the photo-diode pull the pin to ground whenver it triggers and have a pull-up resistor bring the pin high the rest of the time (like I described previously).

mesamune80 · 22nd April 2008, 09:15 AM

i just tried to connect pin 1 via a 1k resistor then to 12v pin 2 to GND ,
and pin 4 to 12V and pin 3 to my microcontroller and i got the reading just 0.92v?

dknguyen · 22nd April 2008, 09:20 AM

Pin 3 should go to ground, while pin 4 should to your uC pin AND go to 5V through a resistor (to pull the pin high when the transistor is not on and not pulling the pin low).

Also, your 1K resistor is too small and would burn out the LED. THe datasheet says it has a 1.7V drop for 20mA if it is a IR LED and a 2.4V drop at 40mA if it is a red LED (do you know which one your device has?)

You should size your resistor so that:
R = (Vsupply-Vdiode)/Inominal

(the extra voltage from the supply that isn't dropped across the diode must be dropped by the resistor, so if you use this extra voltage that is going to appear across your resistor in the equation in V=IR, you can figure out control how much current goes through the LED).

just like when sizing a resistor for a normal LED.

mesamune80 · 22nd April 2008, 09:49 AM

ok,mine is IR LED so my R should be R=(5-1.7)/20mA=165ohms?

,i just tried to put 165ohm but when i block the photosensor the reading could not ground to 0V? Anything wrong ?

dknguyen · 22nd April 2008, 09:57 AM

Quote:

Originally Posted by mesamune80

ok,mine is IR LED so my R should be R=(5-1.7)/20mA=165ohms?

,i just tried to put 165ohm but when i block the photosensor the reading could not ground to 0V? Anything wrong ?

WHen the photo-detector has light on it, the transistor turns ON. THat means when there is light it pulls the pin to ground. WHen there is no light, the resistor pull the pin to 5V.

22nd April 2008, 08:38 AM	#1 (permalink)
mesamune80 Experienced Member Join Date: Oct 2004 Location: Malaysia Posts: 93	OPB702 Optoelectronics Reflective switch Application Hi All, Anyone of you all come across this device? http://www.optekinc.com/pdf/opb702.pdf And anyone can provide the simple connection diagram for this device? Thanks.

22nd April 2008, 08:43 AM	#2 (permalink)
dknguyen Experienced Member Join Date: May 2006 Location: Alberta, Canada Posts: 3,776	The datsheet gives you the internal schematic- a photodiode with a photodetector. Wire up the photodiode with a current limiting resistor the same way you would wire up an LED, and simply wire up the photodetector as an open collector (with a pull-up resistor if you want to measure analog rather than digital). __________________ Disclaimer: Avatar for entertainment purposes only.

22nd April 2008, 09:02 AM	#4 (permalink)
dknguyen Experienced Member Join Date: May 2006 Location: Alberta, Canada Posts: 3,776	You have the photo-diode pull the pin to ground whenver it triggers and have a pull-up resistor bring the pin high the rest of the time (like I described previously). __________________ Disclaimer: Avatar for entertainment purposes only.

22nd April 2008, 09:20 AM	#6 (permalink)
dknguyen Experienced Member Join Date: May 2006 Location: Alberta, Canada Posts: 3,776	Pin 3 should go to ground, while pin 4 should to your uC pin AND go to 5V through a resistor (to pull the pin high when the transistor is not on and not pulling the pin low). Also, your 1K resistor is too small and would burn out the LED. THe datasheet says it has a 1.7V drop for 20mA if it is a IR LED and a 2.4V drop at 40mA if it is a red LED (do you know which one your device has?) You should size your resistor so that: R = (Vsupply-Vdiode)/Inominal (the extra voltage from the supply that isn't dropped across the diode must be dropped by the resistor, so if you use this extra voltage that is going to appear across your resistor in the equation in V=IR, you can figure out control how much current goes through the LED). just like when sizing a resistor for a normal LED. __________________ Disclaimer: Avatar for entertainment purposes only. Last edited by dknguyen; 22nd April 2008 at 09:26 AM.

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22nd April 2008, 08:59 AM	#3 (permalink)
mesamune80 Experienced Member Join Date: Oct 2004 Location: Malaysia Posts: 93	thanks for the information given,but if i would like to give on /off signal to my pic micro controller which i need 5v for high logic how could i achieve that? Thanks.

22nd April 2008, 09:15 AM	#5 (permalink)
mesamune80 Experienced Member Join Date: Oct 2004 Location: Malaysia Posts: 93	i just tried to connect pin 1 via a 1k resistor then to 12v pin 2 to GND , and pin 4 to 12V and pin 3 to my microcontroller and i got the reading just 0.92v?

22nd April 2008, 09:49 AM	#7 (permalink)
mesamune80 Experienced Member Join Date: Oct 2004 Location: Malaysia Posts: 93	ok,mine is IR LED so my R should be R=(5-1.7)/20mA=165ohms? ,i just tried to put 165ohm but when i block the photosensor the reading could not ground to 0V? Anything wrong ?

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