Photosensor/spacing

[jault]

Hey guys i was just wondering does anyone know how far apart the photosensors are supposed to be? i saw a thread that said they mounted theirs, facing down, into a polycarbonate plate they made, but i didnt see anything about spacing, such as how far apart from each other they should be. any ideas or suggestions??

also, do you wire the blue wire to the negative terminal on the power distribution board and the brown to the red? and if so, where does the signal wire connect to ?

thanks,
1652

[Jon Stratis]

For spacing, I would recommend doing some tests. Get a simple board, drill some holes into it, and see what spacing works best for you. Keep in mind that the tape is 2 inches thick, as that will likely affect how you want your spacing.

For wiring, the back of the device tells you which wire attaches to ground, and which to 12V - these should be attaches to the Power Distribution Board through a 20A circuit breaker (in fact, you can attach all 3 sensors to the same circuit breaker).

The signal (either white or black) should be attached to one of the signal pins of the digital inputs on the digital side car. These wires will allow the value of that pin to float (through the pull up transistor) at 5V, and pull it down to ground when triggered, giving you a logical true or false in the code. The white and black wires are opposite each other - one will pull down to ground when it detects the line, the other will pull down to ground when it does not detect the line, thus you only need to attach one of the signal wires, not both.

[DarrinMunter]

Originally Posted by jault

Hey guys i was just wondering does anyone know how far apart the photosensors are supposed to be? i saw a thread that said they mounted theirs, facing down, into a polycarbonate plate they made, but i didnt see anything about spacing, such as how far apart from each other they should be. any ideas or suggestions??

also, do you wire the blue wire to the negative terminal on the power distribution board and the brown to the red? and if so, where does the signal wire connect to ?

thanks,
1652

We placed ours 1.5 inches apart from the center of the photo-eye.
Brown wire is connected to postive 12 volts (red on fuse panel)
Blue is negtive (black on fuse panel)
Now we connected the black wire from the sensor to the white wire of a PWM cable and pluged it into the side car. The red and black wire of the PWM cable are left disconnected. In this configuration when the sensor sees a line, the input on the sidecar will go "low" - the programers will need to know this.
The white wire on the photo sensor is not used.
This is how we are going to be using ours, and we have done testing - modified our 09 robot with the sensors and everything is working great.

Depending on how high you have your sensors you will have to adjusted the contol on the sensor itself.

[mikets]

We are starting to play with the sensors. From my point of view, the spacing is depending on the algorithm. We intend to use an algorithm such that it will create 5 virtual sensors from 3 physical sensors. I would imagine this will require the sensors to be spaced exactly the width of the tape (2 inches). We will see how well it will work in the next few days.

[AndrewN]

The default code that comes with the Labview Autonomous mode expects to have two sensors seeing the line at the same time. The gray gaffer tape is 2 inches wide (FE-00034 sheet 5) . The rest is up to you.

[Jim Wilks]

Originally Posted by mikets

We are starting to play with the sensors. From my point of view, the spacing is depending on the algorithm. We intend to use an algorithm such that it will create 5 virtual sensors from 3 physical sensors. I would imagine this will require the sensors to be spaced exactly the width of the tape (2 inches). We will see how well it will work in the next few days.

Now that most have figured out what line spacing works best, I'm curious what those values are? Just to start off, we've spaced ours at 1.5" on center and are happy with that thus far. Anyone else have something else that works well?

[WizenedEE]

We have 5/2 inches and it's working fine. We're doing a mecanum drive though, so we're just strafing instead of turning.

I programmed it so that when no sensors are on the line, it just keeps going in the direction it was going, which will bridge it.

I guess it does make sense to have them closer together, maybe as much as one inch apart. The reason we went with the larger spacing is so that we could detect the Y, which is a problem. However, it's all about finding the balance.

[mikets]

It turns out that since the sensors are digital with threshold calibration and our algorithm requires that if the line is in between two sensors, both adjacent sensors should "light up", we spaced them such that the adjacent sensors are slightly less than the width of the tape so that both sensors are on the inside edge of the tape. So they are approx. 1.5" center-to-center apart.