Mike:
I got the parts from Digi-Key but that adds a shipping charge to the cost. For me (in Canada) the Digi-Key shipping charge is a bargain ($8.00 CDN to the door usually the next day - incredible service!). I hope that Radio Shack can supply the parts for you. I don't think there is anything wildly unusual required. As I have said before, you will need a filtered 12V power supply. If you don't have one then you should consider the small investment required as a good use of funds because you will be able to use the power supply to run a bunch of other circuits. The draw from the detector is peanuts.
What I didn't include in the cost for the test circuit was the circuit board, but that is not a necessary component. You can build the whole thing and just use a bit of heat shrink tubing to separate the bits.
Good luck. Thank you for your interest.
Please do let us know if the circuit works for you. All the commercial stuff is way more expensive (granted they also have more features) but I think this is a gem that will suit many people.
Dave
I'm just a dude with a bad back having a lot of fun with model trains, and finally building a layout!
Dave,
I may have to try one of these. I need just very basic detection, something to tell me -- Am I clear of a point needed to provide room to turn a train on a wye without bumping the train staged on what is effectively the wye's tail track? Looks like I may be able to find parts at Radio Shack. Will post 'em if I have any luck.
Mike Lehman
Urbana, IL
Digitalgriffen:
I was using a 12V power supply so all I was trying to show was which way the leads were connected. Like I said, I am no expert in this stuff so I apologize if I have labelled the drawing incorrectly. All I know is that the circuit works and the price is right.
Interesting circuit, but it labels +12V and -12V as the primary feeds. That would imply a balanced power supply. I think the -12V is supposed to be ground/common to battery.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
I posted this recently on another thread about train detection, but I thought it might be good to bring direct attention to it be starting a thread all on its own.
This is a very inexpensive infrared train detector which will work with the layout room lights either on or off. In its basic form it is limited in what it can do. For example, there is no delay mechanism so the detector will turn on and off as each car rolls over it. Adding delay circuitry is beyond my comprehension but perhaps someone with a better knowledge of electronics could contribute that sort of additional information. It is also only capable of powering an LED, but I'm sure a relay could be added.
I must state a couple of qualifications: First, I have only used this circuit in test mode because I don't have a layout to try it on. However, I have built three of the sensors and they all work. They will consistantly detect at about 1 1/2".
Second, I have no clue about where I got this circuit from so I cannot give proper credit to the designer.
Here is the schematic and Digi-Key parts list. I think you can use pretty much any LED you choose:
EDIT August 3, 2013. Two key items in the above diagram have become obsolete: For QSC112-ND, use 160-1030-ND or QSD123-ND. Bob Frey whom designed the circuit recommends the 160-1030-ND but either will work. For QEC113-ND, use 754-1600-ND. All parts numbers are Digi-Key.
Here is one of the test circuits, as well as the test track. The tubes in the test track holes are heat shrink tubing:
There are two sensitive bits to observe. One is that the phototransistor (LED infrared detector) must be shielded with heat shrink tubing so only the very tip of the detector is exposed. Second is that you will need a filtered 12V DC power source. When I tried the detectors on an old train set power pack they did not work reliably.
As I said in the other thread, I am an electronic dunce. The fact that I got three of these circuits to work consistently shocked the heck out of me! If I can do it, anybody can!
Now, if someone could add a delay component and perhaps a relay, we would be off to the races! And in economy class to boot!