My first trackside signal and detector

Model Railroader Layouts and layout building
1

Hello all,

Inspired by this months’ MR article on “build your own signals”, I tried my hand at it, and came up with this simple single target.

The mast is 1/16" copper tubing, the LED; a 3mm bi-color LED with 1 annode and 2 cathodes (one for green and one for red) to which I soldered brass rod for the ladder, and styrene for the rungs. The center annode, I soldered to the mast, and then a lead at the base to conduct the negative current. The “lamp shade” I carved out of 1/8" copper tubing with my dremel, and a Kaydee fiber washer for the target face. Obviously, it is too small for prototypical replication, but it’s all I could find to use that fit snug on the 3mm LED.

I found a simple circuit on the internet for making a train detector using a photocell, and purchased the component’s from RadioShack. Here is a link to the webpage, offering the schematic:
http://home.cogeco.ca/~rpaisley4/xComp555photo.html

I used the second circuit on the webpage, and used a 10K for the R2 , replaced D2 with a 12-50V diode, and used the optional R6. I also included two more diodes, one from pin 7 and pin 3, to share the common (or negative) for the bi-color LED. I’m probably confusing some of you, so I will draw a schematic for anyone who is interested in making this same circuit.

I had located the photocell in the center of the track, but realized, light was reaching the photocell between cars, so I moved the photocell over, so the shadow of the couplers would fall on it, sustaining the intended operation.

The LED is green upon approach, and turns red as the train passes the signal. The signal returns to green once the train has passed.

I could have used the third schematic on the website above, but figured I had better try the circuit out, in case I fry something! By the way, I had used a separate pow

2

great video, the first video doesnt work, well it does but it is 0 seconds long…[:)]
great signal looks great! were od you get the photocell and how does it work. thanks![:D]
–Anders!

3

Nice signal Jeremy well done, where’s the link for the order form I need a few!! LOL

Ken.

4

Thanks!

I removed the first video link. I don’t know why it doesn’t play the whole thing.

A photocell is like a variable resistor. When it recieves light, it creates resistance, allowing a small amount of current to pass through it. When the photocell does not receive light, there is no resistance which doesn’t allow current to pass through it.

The circuitry of the 555 timer, controls which LED to turn on, based on the amount of current it recives from the photocell.

I plan to make a few of these, and am going to try the delay circuit next, which will keep the LED red, a few seconds longer after the train has passed.

I have realized, the drawback to this homemade device, is I need ONE for each signal. Good thing resistors come in packs of 5! I can probably fit about 4 individual circuits on one circuit board.

Jeremy

5

Very nice Jeremy, and remember unless you are an anal retentive rivit counter the idea is to imply the realism which you have. The exact size of the target is not important to me, I think you put together a very good signal and will have to ask you how much you would charge or could you do a video on how to. I have never built a circuit before but am willing to give it a go.

6

Neat.

Would using a delay timer (I think that’s also on the page you cited) have avoided the flickering from light between cars?

Kurt Laughlin

7

John, I would be happy to put together a “how-to” for you. Let me get back to you on that.

Kurt, I am not sure about using a delay timer to prevent the flicker between cars. Obviously, the object is to shadow the photocell as much as possible as the train passes over it. Your hypothesis is quite sensible, though it would just add to the circuitry, and maybe a few extra bucks. The timer itself (used in the basic circuit), is like a baseball hitter, it swings at the right “time” to connect to the ball. The photocell is the pitcher.

Jeremy

8

Hi, can someone help me here, last night i build the 3rd circuit, the time delay one but with a bi-colour LED. When the power is on the LED shines green, when i cover the photocell the LED goes dead and not red and stays like that until the delay is over then it changes back to green. My guess is i have wired the LED wrongly.

thanks
Fanie

9

Fanie,

The schematic shows the two LED’s… The trick is that the polarity is reversed between the two, and the annode (+) and cathode (-) of the two LED’s is intercepted at pin 3. If you are using a 3 lead bi-color LED, you need to install a diode between R5 and the annode of the LED, which share pin 3. I don’t have the model number of the diode with me, but it’s the diode with the 50V limit, sold in packs of two at Radio Shack.

Jeremy

10

Jeremy,

It looks great! Now you need to get busy and make about 3,000 of them for all of the forum readers that will want them…

By the way, nice pigs on your video!

Don Z.

11

Can you make one that lights a lantern. Or you can just make it so it raises one of those pointy arms. [:D]

One can hope.

Nice job.

12

It looks great to me, I think you did a fine job on it!
Jarrell

13

Jeremy,
Have you tried it with the lights dimmed for “nite” time running? I only tried a photo cell (on a crossing signal) once on my old layout and could never get it tuned to work with lights dimmed down.

Just curious but an impressive signal as is1

Jim

14

Well, I put a new target on the signal, a larger one. Does that put me in the rivet counter category!? lol. It really just didn’t look right before!

So, you have never built a circuit before? I have never had to show anyone how to make one before. Here is the schematic of the actual circuit after modifications were made from the original. I moved a couple things today (a day after the photo was taken), and I indicated them in the photo:

Yellow arrow - shows I had moved one of the photocell leads over one hole. No change to circuit

Red arrow - shows I had originally jumped the negative input, to pin 1 from the underside of the circuit board, but moved the jumper to the top of the board, indicated from one red circle to the other.

Grey circle on jumper wire - in the photo, the jumper looks like it is in the furthest hole over on the circuit board, but it inserts where the circle indicates.

The power supply, I connected to the center circuits at the other end of the board (not pictured) I intend to put a few of these circuits on one board.

I hope this isn’t too confusing?


You may build your circuit exactly as pictured. The 555 timer pins are correspondent to the printing on the actual chip. So if you can read 555 right side up on the chip, pin 1 will be at your lower left. The only o

15

what did you use for your second target? It looks really good.

I’m going to wire in an old computer power supply ( an ‘AT’ power supply ) to my layout for this kind of thing. They have both a 5V and 12V DC output and are rated for 200w to 250w of power.

16

I went to HomeDepot and found some #6 fiber washers, which I used for the target. I recently built a dual target:

It’s a little out of porportion prototypically, and I didn’t measure anything either. Close enough.

I noticed the image of the schematic doesn’t display full size. Try this one.

Jeremy

17

Jeremy, thanks for the help on the time delay circuit, there is just one thing that you must change on it, after i build it like that it still wasnt working, i removed the connection between pin 3 of the IC and the 2 pins of the 50V diode and then it works fine.

Fanie

18

Jeremy,

Great project. Have you considered placing a second (and third) photo sensor down the track past the signal (in parallel with the first) to have the red aspect stay red as the train passes? It would make the signal function more realistically in both directions.

Mark C.

19

Thanks for the info Fanie, since I have not built the delay circuit myself, I had advised, based on basic circuitry knowledge. I think I might have drawn the diode symbol backward? Glad it works for you!

Unfortunately, with this type of circuit, it is not possible to place more than one photocell, since shadowing the photocell triggers the circuit. If another photocell is added, and one photocell is shadowed, the other cell is still collecting light, which is telling the circuit the train isn’t there yet! I have tried numerous configurations, using diodes, and relays, but it’s not possible. The closest I could get, is using two cells, in which the signal would turn red when it passes, stay red as long as the train was over the other cell farther down the line, at the same time. The problem, is that a short train that would not cover both cells simultaneously, would reset the signal, making the signal go back to green, when it should be red.

I’m happy with this simple circuit, because it is automated, and brings some life to the layout, though it may not be completely realistic. The way I see it, you can’t beat it for a do it yourself, signal and detector project, that costs less than $10.

Jeremy

PS. I noticed the schematic still wont show

20

The Kadee fibre washer is a good idea. I ahve access to a lathe so I used margarine and yoghurt containers plastic, drilled to 3mm and rough cut about 13 or so mm. 9mm is visually right for me so by using a bolt going through the pile of 30 heads, really well tightened I turn about 30 or so.

This process loses the outermost 5 or 6 at both ends but hey there is no other cost. The thin styrene of margarine containers gives a nice cross section of the mast as well. You can see some earlier ones I did using scrap styrene pieces and offcuts before using the containers. Mine are no where near as ornate as yours but the look OK from normal view distance. I just use a dab of paint to create the visor effect… My website www.xdford.digitalzones.com and follow through to the More projects and more views of the layout etc,

Regards from Down Under

Trevor