The circuit for inexpensive infrared train detector was first published in MR in the October 2009 issue. The “K” for a resistor on the Darlington was missing, so that circuit as printed would not work. (It was corrected later.) Another problem was that about 1 year later, the QRB1114 IR Reflective Sensor became obsolete. About two year latter the IR Diode QEC113-ND and the IC PhotoTrans QSC112-ND also became obsolete.
I have chosen some Dig-Key Part No’s as replacement, and added a new circuit.
Thank you Dave for your interest in working with “Inexpensive infrared train detector circuits”. The idea is basically any low cost IR circuits that operates only an LED. Both of these circuits do operate and LED base on the change in the IR light level. The NPN Phototransistor IR can be built to be very sensitive to any form of IR light. When the IR light gets between the cars, you can see a change in the LED level.
In my MR Oct. 2009 article there were a Red and a Yellow, LED in a low light staging area. When the train came in to a single ended staging track, the Yellow came on then the Red. The LEDs would flicker as the train passed through. Then you stop on Red only! On backing out, if the Red went out, you are going in the wrong direction. The two IR sensors, under the track, were about 2 inches apart. A Diode Emitter makes a strong IR light at 40 ma. If you use two of these in series, then you need only one 180 ohm 0.5 W resistor for 12 VDC.
Logic Rail Technologies has more electronic in their product to reduce any problems for other IR light sources. They have 2 or 4 second detector release time to eliminate any flickering. They have screw terminals for inputs and outputs that can control other electronic devices.
To some people time is money, and they can have a complete Model Railroads built for them.
Dave, I know you have started a thread on this subject, and the number of your viewers has become very large. I hope you keep it going at: http://cs.trains.com/mrr/f/744/t/213706.aspx
In-between cirsuits can be found on Rob Paisley’s site. One key to blocking interference is to actually modulate the IR beam. It still won;t work if ambient sources completely swamp the detector, but if the detector only responds to a singla that pulses at some frequency other than AC line frequency, it can discriminate between the actual emitter and ambient light sources with IR content.
Yes, more complex, but still well within the realm od DIY, and not as complex nor as expensive as the Logic Rail circuits.
For the original purpose, in a hidden staging yard, this circuit is plenty adequate. No need to be complex where it is not needed. The simpliest solution, for a given situation, is usually the best.
I also like Rob Paisley’s Model Train web site. “Model Railroad & Misc. Electronics” He has a Main Circuit Index list. Computers and microcontrollers have largely been avoided. The circuits are explained as to how they work, and has a list of Dig Key Part No.
Looking at building some of these detector circuits to test use on my layout.
I read about having two 100ohm resistors in series to increase the sensativity. I model (indoors) in 1/22.5 scale and thus the distance is between 1 1/2 to 1 3/4 inches from top of ties (sensors) to the bottom of most cars. Wondering if you see any concerns with this much distance?
The common answer idea is photocel based, but I want to use the same circuit on the layout in hard to view places, along with in hidden storage. Do not want to mount a light source over each circuit. Will not always have a light source, and with possible night time lighting, means the circuit should not by room lighting based.
So any concerns over the distance from sensors to bottom of cars, in G scale compared to HO scale?
The detectors that Rob Frey is explaining don’t necessarily need an overhead light source, in fact they don’t need any incandescent light at all. They can work by reflecting a beam of infrared light off of the bottom of the cars as the cars pass over the sensors which are mounted in the track between the ties. The sensors have two components. One is an infrared emitter and the other is an infrared sensor. They will work just fine in tunnels and if you use them in other locations they will work in both daytime and night time operations.
Don’t be afraid to ask more questions! I was (and still am) an electronic dinosaur but I have managed to figure out how these sensors work.
Maybe I was unclear on my question, as I am looking for a detector circuit that is ‘not’ light source based. I do not want to use any light source in the setup, that is why I liked the circuit as I read, as both the emitter and detector are mounted in the track. Do not want an overhead lamp, room lighting or such, to be needed. And staying away from blocks or gaps and circuit detection if possible as well.
What I was wondering about though is, the increased distance that I have in G scale. That is, the distance from tie to bottom of an HO car is maybe 1/2 inch, where the distance from ties to bottom of a G scale car is closer to 1 1/2 inches.
One of the circuit comments was to put two 100 ohm resistors in series (why not a 200ohm), to increase the sensativity of the circuit.
Will this circuit still work, and sense the car, when the distance is 3 times the space found in HO scale? Is there a higher resistance value needed to handle the increase in distance I have in G scale?
As you know, the Train detection circuit published in MR Oct. 2009 used a QRB1114-ND. This device is now obsolete.
The replacement parts from Dig Key: http://www.digkey.com are: 754-1600-ND, EMITTER IR 3MM 940NM WATER CLEAR (50 ma). 160-1030-ND, PHOTOTRAN NPN 3MM IR DARK (940NM), Q2F332B-ND, HEATSHRNK POLY 3/32" BLK 4’ (To cove the PHOTOTRAN and eliminate any side ambient light.) and a MPSA27GOS-ND, TRANS NPN DARL BIPO 60V TO.
Frolin, If you do use this IR Detector for your “G” scale Railroad, could you please report back the &
Note that both the IR EMMITTER Diode and the IR Photo Transistor use IR light @ (940NM). I don’t think the new LED style produce IR light in this range? (I have some of them, and Foresselent Lamps in my work shop. The problem of my circuit LED staying on comes when I push the “Sensitivity Resistor” near 470K.) .
Dave, Thanks for the reply. Good to hear others have tested the greater distance and had success. I did email Bob directly, he replied giving this thread link and suggesting I post and ask here, so am doing.
Bob, was wondering about the use of two 100ohm resistors in series, instead of one. Would a 200ohm do the same? Can’t find the posting that mentioned using two, so thought would ask here.
Guys… care to see examples of indoor G/Gn3, that I am referring to? Not casual “G gauge” but true 1/22.5 scale, using both Gauge 1/G for Gn3 NG and Gauge 3 for Std Ga trackage. My layout is not as far along, but my site has photos and videos of my friend Barry’s layout.
Try the ‘Sampler’ video… http://www.frolin.net/cwrr/data/videos.html
To Frolin Marek,
In my material list for the replacement parts, I said: “Putting two 100 K resistors in series, increases the sensitivity. In parallel, it reduces the sensitivity to any light.” Since you did not purchase a 200 K (200,000 Ohms) resistor, you can test this by temporarily putting a 100,000 and a 100,000 ohm resistor in series which is close to a 220K bias on the transistor pins 1 and 2.
Frolin, we don’t need a greater distance in HO scale. I have tried to suggest two way of increasing the distance. One is to produce more IR light, and the other is increase the sensitivity to any light, and then work in a dark area. You could be the first to work with reflective IR light in G scale. I also think it will work for you, but you need to do some testing.
Frolin, If you have just florescent lighting in your train room, then take the IR EMITTER, hold it above your G scale box car, and point it a the IR Photo Transistor, and use circuit #1 The result is
hi guys , got a shopping list going to make some of these detection units as decribed BUT would like to get some kind a circuit board material to build it on so I can attache & or move inside a covered helix …
so I’M looking at boards at digikey site and there a ton , is there a spacific type thats CHEAP and easily cut apart ,for making little circuits as these …??? or somthing other /
I know a board is NOT required for these units but having made things in the past Ive come to beleive it would make it easyer for me. … Jerry
You want plain perfboard with 0.1x0.1 hole spacing. This is available in anything from sizes to hold just one circuit on up to big sheets you can cut apart. You cna also get it at your local Radio Shack. Squares cut from a big sheet were what I used for my Tortoise mounts back when I used Tortoises. To cut it I used wire cutters to snip through a few holes on each side of where I wanted to seperate it, then carefully snapped it along that line.
Hello Tryng to see if this thread is still open I’m am very interested in the circuit and trying to build but have failed to make it work Look for help Thank you Ted
Without being able to see exactly what you have done its kind of hard to figure out why your circuit isn’t working. The only thing I can suggest is to take a look at each of the components and make sure they are all wired the right way round. You could also check out the thread I started prior to this thread on the simpler version of the circuit with both the emitter and receiver mounted in the track. Robert referenced my thread but in case you missed it here is the link:
