Cheap train detection for hidden staging. Ya'll critique my plan.

[cacole]

Using reed switches and magnets seems to me to be a much more expensive and unreliable system than current detection or IR detectors. If I were designing this, I think I would prefer IR and would try to avoid current detection, too, because now you have the added expense of resistor wheel sets to consider.

If you want to continue with reed switches and magnets, a good source to consider is http://www.allelectronics.com

[SpaceMouse]

Since I'm about a month behind G-man here, I wouldn't mind seeing a link to an example or two of IR circuits. I was thinking photo-voltaic, but I can be corrupted.

[Anonymous]

All of the various suggestions here will work, but none really any better than any other. I am an electronics engineer, so lets look at the various suggestions that have been made here and elsewhere.

Magnets and reeds - Despite comments to the contrary, reed switches are quite reliable, if they are of good quality and tested before use. They are hermetically sealed so do not suffer from corrosion. Choice of contact materials can be significant, especially at low currents, but as theya re here proposed to drive LED's that is not an issue. Magents are an issue, polar orientation could be an issue with magnetic uncouplers, but I suspect not. Spacing can be an issue and I would suggest that you could look on eBay for some Neodymium or other intense field rare-earth magnets. Small magnet - strong field - keeps the reed switch further from the rolling stock for safer clearances.

Cross track optical - great for a hidden staging of course, but has lots of visible stuff. Beware of the effects of incandescent room lighting or incandescent lights in locos etc. The sensor should have an IR filter in the optical path. Very reliable, low cost.

Vertical optical - about 10 years ago I designed a train detection system for a hidden staging for a friend which used IR, the roof of the staging area was solid, so we mounted tiny reflectors above each sensor point. This kept al the electronics in one place and is still working today. The detection circuitry is a little more complex, but after the initial cost of making PCB's it is still relatively inexpensive.

Magnetic proximity detection - common in many industrial applications - you have a magnetic field which is disturbed by the movement of the target object, fine if you have lots of magnetic material such as steel in the object. Great for garden railways but despite efforts by some it is really unsiotable for use on small scale layouts - too much plastic and aluminium.

RF Field proximity detection - create a sinmple RF oscillator where the field of the resonant circuit encompasses the sapce where the loco will pass. As pretty much anything goes thourhg the earea the frewuerncy will change and detecting this will trigger whatever is behind it. Complex and offers no real advantage but was a cheap alternative in the 50's and 60's before modern semiconductors.

SPACEMOUSE: Your suggestion of using photo-voltaic detectors (for the others: photo voltaic detectorsa generate a small amount of electric current in response to light - basically like the solar cells you see on roofs etc). Good idea if you can find a sensor with sufficient output to be usable at a reasonable price. But I am not sure that you can get enough form them to be usable at light levels that would be unobtrusive. But it is certianly an interesting thought and if you pursue it further I would love to hear the rsults of your experiments.

Rob Paisley has a simple and elegant 8 channel optical detector board available, you can buy just the bare PCB form him. It can use photo-transistors or CdS (Cadmium Selenide) cells. http://home.cogeco.ca/~rpaisley4/8PhotoDetect.html

John

[grandeman]

QUOTE: Originally posted by jdtoronto

All of the various suggestions here will work, but none really any better than any other. I am an electronics engineer, so lets look at the various suggestions that have been made here and elsewhere.

Magnets and reeds - Despite comments to the contrary, reed switches are quite reliable, if they are of good quality and tested before use.

John, thanks for the valuable info. I had previously heard that mag reed switches were reliable in low current applications.

As for price, I bought enough reed switches, LEDs/resistors, and magnets for about $60. I'm sure Miniatronics isn't the cheapest stuff out there, but their quality is isn't in question.

How do you feel about powering the system off track power? It makes since to me since we use LEDs for loco lighting off track power all the time. It would reduce the amount of wiring. Still, the arguments against it make since as well.

[grandeman]

Space, it looks like I'm gonna be your guinea pig. I'll let you know how this works before you spend any $$$. [8D]

[Anonymous]

QUOTE: Originally posted by grande man

The thought strikes me that if a separate power supply were used, it could have a low voltage and eliminate the resistor board altogether...

NOT!

An LED is a current device, and not a voltage device. An LED won't conduct current until the bias voltage exceeds the minimum, and then it conducts current ike crazy. The resistor is to limit that current flow.

If your power supply was a Thevenin current source set to 20 mA then you'd be in good shape.....

Mark in Utah

[grandeman]

QUOTE: Originally posted by mark_in_utah

QUOTE: Originally posted by grande man

The thought strikes me that if a separate power supply were used, it could have a low voltage and eliminate the resistor board altogether...

NOT!

An LED is a current device, and not a voltage device. An LED won't conduct current until the bias voltage exceeds the minimum, and then it conducts current ike crazy. The resistor is to limit that current flow.


If your power supply was a Thevenin current source set to 20 mA then you'd be in good shape.....

Mark in Utah

Thanks Mark! I love electronics...[:D]

[Anonymous]

One thing I have thought of, Potentially you might want to put some yellow indicaters along the legth of track diagram so you could track progress of the train down the track? I am many years away from having to worry about staging. But that just seems something that should be done incase there is a break down or some kind.

James

[grandeman]

QUOTE: Originally posted by Student of Big Sky Blue

One thing I have thought of, Potentially you might want to put some yellow indicaters along the legth of track diagram so you could track progress of the train down the track? I am many years away from having to worry about staging. But that just seems something that should be done incase there is a break down or some kind.

James

That's a good idea that may come to pass. We'll wait and see how the original plan works and add extra LEDs if needed.

Now for an update. I am going to use a separate power supply. It'll be a 12v unit rated for 1 amp (since that's what I found in my "junk" box [:D]) . The wiring will be a common power lead bussed thru board mounted resistors to the LEDs. The reed switches will complete the ground side of the circuit for each staging track. Here's a pic of tonight's progress. The terminal strips on the sides will be connections from the 4 conductor phone wires (6 total) going out to the reed switches (each yard will have a ground line from the power supply). The black wire in the center of the pic (verticle) is the Positive lead that will be connected directly to the power supply. The other is a buss wire between the resistors. The resistors are soldered together on the power side to buss them together


Comments, questions or heckling from the peanut gallery??? [:D] You guys pick the new plan apart for problems I haven't thought of.

[scubaterry]

Grande man - I agree with markpierce! I plan on putting in a micro camera on my hidden stage area hooked up to a cheap 12 inch TV. As a matter of fact I may put several cameras around the layout just for the heck of it to keep track of things so I don't have to get off my butt. But seriously I have seen the micro cameras going for 60 bucks lately. You don't need the sound version, more money saved. You could pick up a used 12 in(or so) TV at a flea market or yard sale. You can buy brand new ones for less than 70 bucks. Probably more than you wanted to spend but far simpler and bullet proof (??)
Terry

[roadrat]

I have to agree with "scubaterry & markpierce" the closed circ TV system is easy and fool proof (well sort of) if you can see the track then you know if there is a train there.
you can even shave off a few extra $$ by buying an older B/W camera.

just my [2c]

bill

[grandeman]

Hey guys. Thanks for the input. I think CC TV is great but we'll have three yards to monitor and the North yard will be a minimal distance above the South yard. I'm thinking TV could be difficult to do.

[grandeman]

Hi all. Here's an update on tonight's progress.

Loaded West Yard. From the water heater until they appear on the layout, trains only travel approx 6 feet.


Installed reed switches. These are for the west yard's red LED's, but the green LED switches were installed tonight as well.


Continuity!!! The test loco tripped all eight switches with no problems. It's hard to see from the pic, but the meter reads one ohm.


The west yard detection is coming along nicely. I need to run the ground side wire to the yard and mount the indication panel. One of the panel's red LED's still has to be installed. Hopefully we'll test the system soon!


One last update and I'll let this dog lie. Today I finished the South yard, installed the indication panel, and wired the detection to the panel. So far, the system is working better than I'd hoped!!! I think we're really going to be happy with it.

ETA, the system is complete. Here's a shot of the indication panel during our first test ops session!

[SteelMonsters]

This might be a cheap option if you want a bunch more for whatever reason.

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=171871

[grandeman]

QUOTE: Originally posted by SteelMonsters

This might be a cheap option if you want a bunch more for whatever reason.

http://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?langId=-1&storeId=10001&catalogId=10001&productId=171871

Thanks for the great link!

[Anonymous]

QUOTE: A magnet and a few switches more complicated than a closed circuit TV system? When did that happen?

I am somewhat of an old fart so I chuckled too. I do know that it all happened long enough ago for there to be lots of cheap cheap deals on old stuff.

One swap meet deal got me a bunch of surveillance cameras; 3 low lux BW lens on PCB cams, 1 1/4 lux and IR sensitive BW lens on PCB cam and 2 high res BW PCB with lens adapter for 16mm movie camera lens ..$25 the lot.

Another deal was 2 full size Panasonic camcorders for $20. good video on both but only one records.

I also have a Minolta and a couple of Sony handycams. Good cam No corder.

BW or Monochrome monitors are free for the taking. I already had a few. My total cost for 11 camera setup including Radio shack switch boxes is still below $100 CANADIAN!