Thread: Optical sensors

Hi!
Does anyone here know of some really fast optical sensor that could detect a great decrease in the amplitude of the light shining on it?
What I mean is that I will have some sort of light emitting unit that will shine continously on the sensor, and that breaking this ray of light would make the sensor respond.
Thanks in advance!

You mean like the sensors an automatic garage door opener has?

Do a search on:
Photodiode

You will find all kinds of cheep things you can get.

Originally Posted by Harold14370

You mean like the sensors an automatic garage door opener has?

I don't know exactly know how they work, so it's hard to tell.

Originally Posted by thyristor

Originally Posted by Harold14370

You mean like the sensors an automatic garage door opener has?

I don't know exactly know how they work, so it's hard to tell.

Well, there are two devices, one a source of infrared light and one the sensor. They are mounted on opposite sides of the garage door opening. When the light beam is broken, such as by a person walking through the doorway, the garage door will reverse if it is closing. The one I have will turn on the overhead light if the door is open and somebody walks through the doorway.

Here's a kit for a photoelectric beam sensor.

http://www.apogeekits.com/photoelect...m_sensor_2.htm

Originally Posted by Harold14370

Originally Posted by thyristor

Originally Posted by Harold14370

You mean like the sensors an automatic garage door opener has?

I don't know exactly know how they work, so it's hard to tell.

Well, there are two devices, one a source of infrared light and one the sensor. They are mounted on opposite sides of the garage door opening. When the light beam is broken, such as by a person walking through the doorway, the garage door will reverse if it is closing. The one I have will turn on the overhead light if the door is open and somebody walks through the doorway.

Here's a kit for a photoelectric beam sensor.

http://www.apogeekits.com/photoelect...m_sensor_2.htm

Ok, thanks! I'll take a look at it.

You may alternately tear open an old VCR and (IR) remote control... or for very short range many kinds of data drives have an opposing pair of LEDs to see a hole or tab etc... strangely an LED may emit light or sense it.

Originally Posted by thyristor

Hi!
Does anyone here know of some really fast optical sensor that could detect a great decrease in the amplitude of the light shining on it?
What I mean is that I will have some sort of light emitting unit that will shine continously on the sensor, and that breaking this ray of light would make the sensor respond.
Thanks in advance!

There are lots of optical sensors out there.

As Harold noted garage door openers use them for safety. Some are more sensitive and more sophisticated.

I know of at least one in service that can detect a single photon from a specific spectral band, and trigger an alarm.

Femtosecond lasers may be of interest to you. They have developed sensors which can detect pulses of light which last for only a femtosecond, and even up to an attosecond!!!!!

You can buy a small bag of photodiodes at Radio Shack. It'll cost something like 2.00

Ok, thanks a lot for your answers. To specify my question a bit more, I intend to use the device for measuring the velocity os a small ball by letting it pass two of these devices which will be at a known distance from each other. The velocity of the ball will range from about 0,5 m/s up to 4 or maybe 5 m/s.

To DrRocket: That's sounds interesting, but maybe they're a bit too expensive. How much are they?

To Waveman28: That too sounds interesting. However, the same problem as stated above, how much do such sensors cost?

To Pong: How much does the light of these senors spread? I have a feeling that the light has to be pretty much a ray.

To kojax: I'll have a look at them.

It seems that you are trying to reinvent the shooting chronograph
http://www.larrywillis.com/chronograph2.html
except I haven't seen one that works on projectiles that slow.

Originally Posted by Harold14370

It seems that you are trying to reinvent the shooting chronograph
http://www.larrywillis.com/chronograph2.html
except I haven't seen one that works on projectiles that slow.

I have used Kennhy Oehler's 35 P for things as slow as an arrow (175 fps or so), but I don't think it would work without showing an error on something as slow as the OPs ball. Maybe he could use a stopwatch, or a calendar.

http://www.oehler-research.com/

Originally Posted by thyristor

To Pong: How much does the light of these senors spread? I have a feeling that the light has to be pretty much a ray.

Well, how small is the ball you want to time? How tightly can you mount the sensors / emitters?

Another possible freebie or garage-sale salvage: http://www.slotcaracademy.com/slot-c...lapcounter.htm note the computer interface and "Timing in 1/10000 of seconds".


If you're handy with electronics I suggest you start by putting a multimeter on an ordinary LED, and hitting it with $30 level-laser available at any hardware store.

Sorry I didn't reply before. The ball that I will use is about 5mm in diameter and so the sensor can be no closer than 5mm to the light source.