I have a building that has dock doors on it and I would like to add dock door lights (green - if door is available/ red - when door is occupied by a trailer). I was thinking of using a photo - optic diode to detect the light when no trailer is at the door to make the green LED light up and the red LED light up when the door is in use.
My problem is I cannot find on the internet any reliable source(s) that leverages this type of circuitry using the photo diodes where by one LED is on in one scenario and the other LED toggles on in the other scenario. I saw a couple YouTube videos that use a magnetic relay to do the switching so I don't know if that is something I would need to include - the problem with those videos are they either only use one LED or they use a toggle switch to make one LED on and the other off. Also a lot of the videos I watched last night used these circuit "bread boards" that do not require soldering. Are those pretty good nowadays? I have never used them before.
So I guess my questions are these:•Should/can I use a relay switch with the photo sensor?
•Does anyone know of a good resource/reference URL/material that I can refer to assist me when building this?
•Where could I obtain the needed components for this?
The components I think I need would be...
green LED, red LED, one or two photo diode sensors (for light detection), circuit board of some sort, resistors of some resistance (not sure what type yet), possibly a light sensitivity adjuster (???) - to control how sensitive the photo diodes need to be.
The icing on the cake for this whole small project then would be if the above is do-able and easy to do, I'd like to make the green LED pulse - to match a prototype dock door light detection system.
Sort of off topic, but it seems to me that it would be obvious if there was a trailer at the dock. Unless it is an invisible trailer. What are these lights really supposed to indicate?
EDIT: Oh, wait a minute. I guess the trailer is backed into the building and then the door is closed?
SOunds like a job for an Arduino - to be able to have the pulsing green LED, plus detection capability to switch to a red LED. All you really need for detection is a photocell under the pavement where it would eb covered if a trailer were in place. Unless you do night operations with the lights out, in which case you would need a light source as well that gets blocked when a trailer is in place. There are several Arduino examples for the detection part, an IR LED is pulsed and an IR phototransistor is read, that way ambient light has no real effect because the detector is looking for the pulsing not the general light level. Using the detection status to activate one of two output pins would be pretty simple.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Actually the Red/Green lites on Truck dock doors, are not to define whether or not door is accessible...should be obvious, per Maxman. The real reason, newer docks with the lites are for...lock, unlock hooks that swing up from the bottom of the door opening where the dock-plate is and grab the ICC bar that is at the back of the trailer,(which some people call bumper) so the trailer cannot move. There are lights on the dock itself next to the door, that a worker controls, especially when using a fork lift truck. The outside lights are mainly to let the Truck driver know that the Trailer is locked to the dock....so He can't move it without it being released.....big safety feature, especially for the dock workers. Many a times.. drivers would pull a trailer from the dock, without checking to see if anyone was working in it or even remove a tire chock. Also stops the workers from going in, without checking, to see if it's locked. Sort of like a Blue light rule.
Take Care!
Frank
Arduino feels like overkill. Use a SPDT or DPDT relay, such that you have both Normally-open and Normally-closed contacts. Wire one LED to the NO side, one to the NC side.
My issue, though, is the photo detectors. The difference in light levels will NOT be 100%, so getting the dectector to reliably tell may be tricky. Have you got prior experience with the detector? If not, you might consider using magnets instead, glued to the bottom of the trailers (inside or out). Just an idea.
Frank:
Interesting information.
Just out of curiousity, when were the trailer locking systems put into use?
Henry V:
Just in case nobody has said it, WELCOME to the forums!!
I would suggest using IR (InfaRed) detectors instead of the photocells. IR will allow your sensing system to work in both day and night scenes. The only significant difference in the setup is that you need two components instead of just the photocell. One is the IR transmitter and the other is the IR receiver. They can be mounted side by side with both pointing at the trailer, or they can be set up as a cross beam. In your case I think the side by side configuration would be more logical. You have to use some heat shrink tubing on the IR LEDs to focus them on the trailers in order to limit false signals from things like florescent lighting.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
hon30critterJust out of curiousity, when were the trailer locking systems put into use?
Dave,
The actual law concerning chocking trailers at docks etc. was revised in 1981 and they got a lot stiffer in fines and such. The locking device We are discussing, with the lights was not the only type, but most effective. I saw them start popping up at large facilities, like all Automotive Plants and suppliers in the 84'era! The Truck Line I worked for did not have any such thing, mainly due to being cost preventive on an older dock and We had only an 84 door dock, but still 84 x 1,000 is a lot of dough! LOL. We had a proven system.....two way radio, dock foreman closing door...LOL.
CF (Consolidated Freightways) near My house, had a 194 door dock...half of their dock, had the lights installed before they went out of business....HUH? You would never know the dock was there now. The Village leveled the property and built a Soccer Stadium there with all the whistle's and bells... Called Toyota Park..LOL Makes One wonder, who's controlling what.
Some info:
https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=DIRECTIVES&p_id=1717
Henry Vicenik,
Forgot in My last post...
To The Forums...
If I were You...I would keep it simple...still having the effect..DPDT Center off toggle switch, mounted near fasia of facility or control panel. One Grn 1.8mm flashing LED and one Red 1.8mm flashing LED. toggle controls which one You want on....will flash on its own until turned off, 12vdc supply. Mount LED on the inside side of door opening with a smaller hole drilled in front of it so light only shines through hole size You decide on, for scale.
One source for flashing LED's: There are other's.
http://www.modeltrainsoftware.com/bl-213-f.html
Frank's got this, with early to mid-80s implementation.Our facility had about 120 doors, so the contractor was there for awhile. This would also be the time when the "ICC bar" on the rear of trailers became very important. Before the locking requirement was made, you'd see those ICC bars all over the place in terms of height, construction, etc and even whether they were maintained if bent, etc. After implementation, most trailers were seen with a much more standardized rear bumper arrangement to permit reliable locking.
The red light indicates a trailer is locked to the dock. A green light indicates the dock is unlocked. However, green can be on when a trailer is sitting in the dock, either loaded but not opened yet or loaded and ready to be pulled, too; don't assume green means no trailer in the door.
I never had any real close calls coming out of a trailer before locks, but did "take the ride" down the lot several times when a spotter got under it with me working a load in the nose of the trailer. No point in rushin to try to get off, just go for the ride and hope the overhead door into the building at the next stop is open so you can get in. Worst case is getting taken to the line and dropped -- you can get off the back easily enough, but the trailer has to go back to the dock to get your electric pallet jack unloaded.
BTW, all this could make for an interesting scene on the layout if you have a big warehouse.
Mike Lehman
Urbana, IL
Mike Lehman,
After reading Your post, it reminded Me of something that took place that I havn't thought about in years, but will always make Me laugh My butt-off when I do.
Our home office, which was in St.Paul MN. had a company sign built for the front of our building in Chgo. It was shipped in one of our own road trailers unloaded and set on our dock. Two mechanic's from our shop, took a city tractor trailer and backed it into the dock, loaded the sign on the trailer, which was 4ft x 15ft and closed the roll-up door on the trailer and went downstairs in front to grab a coffee to take back to the shop with them. My other spotter friend and I were watching this go on......when they were out of site, We took the sign off the trailer and put it back on the dock, where they got it from. They got in the truck and drove off...only to return about 15 min. later back on the dock scratching their heads. They probably would never have found out what happened...but My friend gave it away by asking them, ''when the hell You guy's going get this sign off the dock'' LOL LOL. To see the expression on their faces, makes Me laugh to this day. Moments in life.
You would find those trailer locks on most all, on the all-weather dock doors that look like the ones in the pic'. The lock would be behind the orange dock plate on this type. Most newer ones, the trailer has to be locked first before dock plate can be raised.
Pic' is void of all details, due to a work in progress.
Frank,
Those are some long folding lips. All of ours were in the 18" range, with the lock mechanism clear of that and immediately below it. Trailer needs to be locked before plate will operate IIRC.
Mike,
Yeah they look that way, but are actually two horizontal pieces, that fold in half when lifted and back, then on back of trailer. You can't tell they are two pieces in the photo.
OK, that explains the difference. I've seen ones like that before, just never operated any.
I suspect what's going on is that those may be an integrated solution to the dock plate and lock, all in one. Like many done at the time of the new requirement, our install already had the plates and pits to fit them. They basically attached the locking mechanism to the dock face below the folding lip. For a new install, a deeper pit to accomodate an all in one solution wouldn't be an issue. For those modeling more close to the present, might be worth looking into what year those all in ones were introduced, if you like to slice your cheese that thin.
Frank thank you for the suggestion and the link...(using the blinking LED's simplifies the process. The DTDP toggle switches are probably the least expensive way to go. Plus I can wire the circuit up quicker this way. Although I do appreciate everyone's suggestions. You background on the loading dock lights was enlightening to me. I hadn't realized that was their use! Thank you for the information.
Henry
Henry,
You are quite Welcome....I don't know how far You want to get into this or how much You want to spend, but they do make even smaller LED's in the shape of SMD's in NANO...now You are talking extremely small...smaller than the size of the head of a straight pin. I have just begun experimenting with them, after having them on a NANO quad copter.....that I still can't get the knack to fly the way I want......hovering, is a challenge! Any way, here is a link to some pretty interesting stuff, should You like to take the time to do a little navigating on the site. Many interesting things are on the market now! I have purchased from them 7 times already and am completely satisfied. I will let You know, when I receive the one's I ordered, Red, Yellow, to see if the flash rate would be acceptable in Your application. I'm thinking they may be too fast, but I''ll let You know, the details.
The one's I ordered, are for a 1/87 scale metal casting kit, Tandem axle Truck Boom Wrecker from the 50's, that I am redoing.
http://lights4models.com/index.php/led/flashing-led/nano/red.html
Edit: Thought I would show a couple pic's of how small those SMD's are. Look at the left side bottom of truck by tires...that little tiny thing with the wires....next pic' I'm holding it in My fingers lit-up. The Truck is stripped of paint, just sitting on chassis in piece's...have a few holes to drill yet!