What I need to know is how the "electronic eyes" work. Do they send a
signal back to the opener ? Are they just a voltage loop that is opened
when something crosses the beam ? I believe thay are powered by DC
voltage.

The reason I ask is I am trying to build a timing clock for a guy and his
soap box derby car, and he got a pair of sensors for us to use and timing
spots to start and stop the digital stop watch, I need to build.

John65stang wrote:
What I need to know is how the "electronic eyes" work. Do they send a
signal back to the opener ? Are they just a voltage loop that is opened
when something crosses the beam ? I believe thay are powered by DC
voltage.

The reason I ask is I am trying to build a timing clock for a guy and his
soap box derby car, and he got a pair of sensors for us to use and timing
spots to start and stop the digital stop watch, I need to build.

Hi,
Typically it is a IR emitter and sensor set up. If beam is interupted,
sensor generates signal. From this you can rig up anything you want.

Why don't you use a transponder setup for radio control car/boat/airplane
racing?
Here's one that is used for rc cars; http://www.rclapcounter.com/.

Rich
http://www.garagedoorsupply.com



"John65stang" wrote in message
news:35d60e4bd28b26e7692c213fc677190e@homerepairli ve.com...
What I need to know is how the "electronic eyes" work. Do they send a
signal back to the opener ? Are they just a voltage loop that is opened
when something crosses the beam ? I believe thay are powered by DC
voltage.

The reason I ask is I am trying to build a timing clock for a guy and his
soap box derby car, and he got a pair of sensors for us to use and timing
spots to start and stop the digital stop watch, I need to build.

Be aware that most photoelectric sensors work by pulsing the LED. They do
this to get a higher brightness out of it (example: 50% dutycycle at twice
the power). As such if you use it to try to measure time there will be a
certain "quantizing" error in your measurements. The ones I'm familiar with
worked from 60hZ to the hundreds of Hz region. Don't know if thats enough of
an error to influence a soapbox derby outcome. (Can a person holding a
stopwatch be more accurate than 1/60th of a second?)

THere are of course special analog sensors that are used for time critical
measurements but I doubt they would be used on a garage door.

"John65stang" wrote in message
news:35d60e4bd28b26e7692c213fc677190e@homerepairli ve.com...
What I need to know is how the "electronic eyes" work. Do they send a
signal back to the opener ? Are they just a voltage loop that is opened
when something crosses the beam ? I believe thay are powered by DC
voltage.

The reason I ask is I am trying to build a timing clock for a guy and his
soap box derby car, and he got a pair of sensors for us to use and timing
spots to start and stop the digital stop watch, I need to build.

Tony Hwang wrote:
John65stang wrote:
What I need to know is how the "electronic eyes" work. Do they send a
signal back to the opener ? Are they just a voltage loop that is opened
when something crosses the beam ? I believe thay are powered by DC
voltage.

The reason I ask is I am trying to build a timing clock for a guy and his
soap box derby car, and he got a pair of sensors for us to use and timing
spots to start and stop the digital stop watch, I need to build.

Hi,
Typically it is a IR emitter and sensor set up. If beam is interupted,
sensor generates signal. From this you can rig up anything you want.


Actually, it's the reverse, at least for the sensor itself. When light
energy hits the receiving sensor, it generates a voltage which is then
detected. If he wants to use what he has,he can use a VOM to measure
it, then rig up an apporpriate circuit. However, I'd check Radio
Shack, as they may have cheap kit or already built hobby type solutions
for this.