OptoCoupler

Thread Starter

mpuvdd

Joined Feb 11, 2007
50
Hello all,
I recently picked up a tcrt1010 opto coupler and am having trouble figuring out how to make it function. The coupler has two pins for the IR led, and two for the photo-transistor's collector and emitter. I'm going to use the coupler for my rpm monitor project and I want it to output a 1 if it sees white, but a 0 when it sees black. There is only one circuit in this project and therefore the collector and led anode are connected w/ a resistor to vdd, (I think). What kind of resistances and stuff do I need to make it function in this way. The tcrt1010's datasheet is provided here: http://www.vishay.com/docs/83752/83752.pdf.

Thanks a lot,
mpuvdd
 

hgmjr

Joined Jan 28, 2005
9,029
It would be a good start for you to read the application notes contained on the Vishay website.

Application Notes

The links to the application notes are on right-hand middle portion at the page linked to above.

There is one on reflective sensors which applies to your application and one on Assembly Instructions that you will benefit from reading.

The datasheet itelf contains a lot of useful information specific to the device.

hgmjr
 

Thread Starter

mpuvdd

Joined Feb 11, 2007
50
Okay,
So say I have a 5V source, provided by a 78l05 voltage regulator, how do I provide a 1.6V, 50mA source to the optocoupler's led, and at the same time source 5V and .3 to .5 mA to the optocoupler's collector?
Thanks,
mpuvdd
 

Papabravo

Joined Feb 24, 2006
14,453
To ask such a question reveals a gross misunderstanding of the optocoupler's purpose. It is used when you have circuits powerd by two different sources that must be isolated from each other.

The input side of an optocoupler doesn't care about the voltage available, only the current. A series resistor will do just fine. On the output side you put the load resistor in the collector circuit to make an inverter or in the emitter circuit to make a follower. Again the voltage doesn't matter. If you don't already have two supplies, which must be isolated, then you don't need an optocoupler.
 

Thread Starter

mpuvdd

Joined Feb 11, 2007
50
OK, but an opto coupler is still a good choice for monitoring a rpm disk, right? Is there something better that won't interfere w/ the motors operation (e.g. anything touching or slowing down the motor's shaft)? Seems to me that you could somehow incorporate a coupler into a circuit w/ only one battery source, or is this completely out of the question? Well thanks for all of the help so far, I'm a beginner.
mpuvdd
 

thingmaker3

Joined May 16, 2005
5,084
"Reflective Optical Sensor" and "Optocoupler" are two very different things. The Vishay product from the first post is a reflective optical sensor, not an optocoupler.

And, yes, it will work fine with an RPM disk - if the disk sections alternately reflect and absorb the 950nm wavelength.

Put a 100 ohm resistor between the LED anode (A) and your 5V supply. Put another resistor between the detector's collector and your 5V supply - at least 100 ohms, but more is okay. Tie the LED cathode and the detector's emitter to ground. Collector voltage will alternate between 5V and near 0V with the reflective optical sensor within 1mm of your rotating disk.
 

Ron H

Joined Apr 14, 2005
7,014
"Reflective Optical Sensor" and "Optocoupler" are two very different things. The Vishay product from the first post is a reflective optical sensor, not an optocoupler.

And, yes, it will work fine with an RPM disk - if the disk sections alternately reflect and absorb the 950nm wavelength.

Put a 100 ohm resistor between the LED anode (A) and your 5V supply. Put another resistor between the detector's collector and your 5V supply - at least 100 ohms, but more is okay. Tie the LED cathode and the detector's emitter to ground. Collector voltage will alternate between 5V and near 0V with the reflective optical sensor within 1mm of your rotating disk.
He said he wants a 1 for white and a 0 for black. Putting the resistor in the collector circuit will give the opposite. I wonder if that matters (can't see why). Putting the resistor between emitter and GND with the collector to vcc will give the desired results. The load resistor needs to be a much larger value than the LED resistor, because the typical current transfer ratio is only 2.5%. If you make it too large, ambient light might cause a problem. I would start with 10k.
If you can use a tach disk with holes or slots, a photointerrupter is a much better solution.
 

Thread Starter

mpuvdd

Joined Feb 11, 2007
50
All right,
So I've chosen to go with some an opto interrupter (not sure which one). Oh, by the way, now that I really think of it, it really doesn't matter if it outputs a 1 or 0 when white's detected because either way it goes through a XOR setup that sends out a pulse to a counter every time the sensor transitions from 1 to 0 or vice versa. But one more question; what's the difference between an opto coupler and a reflective optical sensor? Well, thanks so much for all of the help that you've all given me. I'm an optical sensor expert now :)
mpuvdd
 

Ron H

Joined Apr 14, 2005
7,014
All right,
So I've chosen to go with some an opto interrupter (not sure which one). Oh, by the way, now that I really think of it, it really doesn't matter if it outputs a 1 or 0 when white's detected because either way it goes through a XOR setup that sends out a pulse to a counter every time the sensor transitions from 1 to 0 or vice versa. But one more question; what's the difference between an opto coupler and a reflective optical sensor? Well, thanks so much for all of the help that you've all given me. I'm an optical sensor expert now :)
mpuvdd
An optocoupler (c'mon, look it up) has an LED and a phototransistor encapsulated in the same package, looking at each other. They allow signals to couple between systems that may have thousands of volts between them, or a lot of noise on one system's ground relative to the other, or...
 

thingmaker3

Joined May 16, 2005
5,084
Yeah, Ron. You know... chicken. He's asking if an optocoupler can allow signals to couple between systems that may have chicken. My initial impulse is to say "no," but I've no experience with chicken in electronic systems. Maybee either Beenthere or PapaBravo (or both) have experience with such. Or not.
 

Ron H

Joined Apr 14, 2005
7,014
Yeah, Ron. You know... chicken. He's asking if an optocoupler can allow signals to couple between systems that may have chicken. My initial impulse is to say "no," but I've no experience with chicken in electronic systems. Maybee either Beenthere or PapaBravo (or both) have experience with such. Or not.
Yeah, I should have mentioned asparagus. I'm not so sure about chicken...
 
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