I am having trouble getting the circuit described in Robert Frey’s October 2009 issue of Model Railroader to work. Does anyone know if there is an error in the circuit or have any trouble-shooting thoughts? I have hooked everything up according to the diagram on a breadboard.
I kind of wondered about that !
I looked at the wiring diagram and SOMEthing just didn’t look right to me - but I couldn’t put my finger on it ! (?) Hoefully MR will print a correction if necessary.
Mark.
Several resistor values were not right. I recalculated all of the values according to Ohms law and the specifications of the reflective opto sensor and transistors and found several errors.
The two resistors marked as 470k are WAY off.
Might have flopped them around. The IR LEDs in the sensors are 1.7V, two in series powered by 12 volts with 20ma would be a 430 ohm resistor, 470 being close enough. Also looking at the picture of the circuit, the middle resistor, which may or may not be the middle resistor int he schematic, is 470 ohms - yellow, violet, brown. Can’t see the colors on the two standing up.
–Randy
Randy, you are correct!
I replaced the 470k ohm current limiting resistor for the IR-LED pair with a 470 ohm resistor and the circuit worked.
How do I get a message to MR so they can print a correction before others run into the same problem?
John
I suspect someone had already seen this. However there is an option to contact the editors somewhere back up at the top of the site, I used it to submit a correction to a DCC comparison article and was later contacted by Andy Sperandeo because they wanted to print my comment. My only claim to fame ever - I had a letter to the editor printed in MR!
It’s Contact Us under the Our Magazine menu, I think.
–Randy
In the October 2009 issue of Model Railroader, the article “Simple train detection” in the Fig.2 Wiring diagram on page 65, the 470 and the 470K values got interchanged. The value between the two 1K resistors should be 470 ohms. (The 470 ohm resistor controls the 20 ma. current that flows through the “E” of the Infrared sensors.) The value to the left and right for each transistor is 470K. (By making the size of the 470K resistors across each transistor smaller, then the “S” sensor can resist higher amounts of ambient lighting (such as incandescent overhead lights), but then the sensing distance to the bottom of a HO car becomes less.
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Robert,
Thanks for taking the time to clear this up and for providing more great information! [tup]
Hi Robert: The artical was and still is of great value to those of us that prefer to “Do it Ourselfers”. I know nothing of Omns law and also nothing of wireing this sort of thing. But, I was looking for a way to detect train movement and you supplied it, thank you! I had a bit of trouble at first, but solved the problem and the system works great! Now, there is another problem. Digi-Key has run out of QRB-1114-NB IR sensors. They sugested two different ones. The QRD-1113-ND, QRD-1114-ND, which is a smaller emitter sensor and I think might work better for me. Also the 365-1014-ND reflective sensor. I havent’t had any luck with either one, do you, or have you tryed to replace th QRB-1114-ND? I am very interseted, not only for myself, but our club has built a dispatcher’s booth and this application comes in very handy for tracking the locations of the various trains .
John
John, Try the following: http://www.onlinecomponents.com/buy/FAIRCHILD/QRB1114/ Let me know if you were able to buy some? Bob Frey
Hi Bob.
Thanks for the quick answer! I was at our train clubs open house yesterday, it was a good day.
I took your advice and went to Fairchilds web and wal la some QRB 1114’s So I ordered some. That was some good news. I tryed your up dated diagram on the QRD 1114 and the other one, don’ have the number in front of me right now, and I couldn’t get it to work. Since the QRB’s 1114 are coming out I’ll wait and do the double sensors. I notice they are a little bit light sensitive, but work very well in my hidden staging yard and two main lines. I just love following the trains via the led’s on the routing boards. I can’t hardly wait to give these sensors a try at the club, but we have a lot of light there.
I went into your web site, WOW now thats a great layout, there isn’t anything within a 100 miles of here that big.
I worked for the espee for 35 years and then it was bought out by uncle pete. Never got use to all of those yellow horses running around the area.
Any how, thanks again for the info. if you have an idea on how to make those sensors work with so much light, the help would be appreciated!
Thanks again, John
Hi Bob.
I ordered the QRB 1114, as you saw that were going to be available May 1st. They sent me an e-mail this morning, saying that now they may be availble in about 12 or 13 months. Did you try out any of the other sensors that I tryed and couldn’t get to work?
The sensor numbers are, 751-1032-ND, which very small and you would only have to drill about a 3/8th inch hole and cut a very small bit of cork away. The 365-1014-ND and the QRD-1114-ND I’ve also tryed with no sucess. The 365-1014-ND are the same size as the QRB-1114-ND, which I have already cut into the table with anticaption of receiving the QRB-1114’s. No luck there!
If you have any luck or the time to spend on the above sensors or some othe sensor that works, could you please let me know. Myself and a couple others in our club would like to install them on their layouts and also install a few at the club.
Well, thanks again
John
Hi again John, I think your IR Sensor: 365-1014-ND should work. I revised my circuit picture with it. If you don’t have a Transistor: MPSA27, then any two NPN transistors can used if connected as shown in the CIRCLE Picture. Also see http://cs.trains.com/trccs/forums/p/162676/1801342.aspx#1801342 (11-21-2009 4:37 PM Reply from cacole) Robert Frey 
Hi Robert:
Thanks for your quick reply! I’ve tried it the way you have drawn it out with the same components. But knowing me there is probably a wire wrong some place. I’m busy the rest of the week, but I’ll give it another try next week.
Thanks again for giving this some thought. It’s so nice to have people like you around to give us folks help that don’t have the knowledge a helping hand.
O.K. Thanks Again
John
Bob - I wired it per the above diagram for a single detector, but the led is lit and remains lit at all times. Any insight as to what I may have done wrong? Tom
Hi Tom, I don’t actually have an OPB742 Sensor, but you do. The units are the same size, and the electrical data at Digikey is very nearly the same, for both the IR Emitter and the IR Sensor. This looks to me, as to be a very good replacement part. 1. Measure your +12VDC 2. With +10VDC across the 470 ohm resistor, then there is 20 ma flowing through the Emitter (The Emitter is the 2 Volt diode in OPB742 the that produces the IR light.) 3. I assume you also have a MPS27 Transistor? The Base (pin 2) is connected to the output arrow of the IR Sensor. (If you don’t, then any two NPN transistors connected as showed in the circle will do.) 4. A 470,000 Ohm resistor (470 K) is connected between the Transistor Base (Pin 2) and Emitter (Pin 1), and the 680 Ohm resistor, limits the DC current to 11 ma. to operate the LED. If the wiring is correct, holding your finger on the Sensor hole, the led should be OFF. Moving your finger about ½ inch away the led should be ON. Completely removing your finger from view, the led should be OFF. (Because the IR lighting is not bouncing off of your finger.) If the led is ON, then you have Incandescent lighting in your room. The IR sensor is also sensitive to sun light but, is not sensitive to Florescent type of lighting. Buy putting the +12VDC power directly to the IR Sensor, this removes the IR lighting diode. Then using only your Incandescent room lighting, when a car is over the sensor, the led will go OFF. Robert Frey
Bob, many thanks for the reply. I discovered that for some reason the florescent lighting in the room is being picked up by the sensor and keeping the LED lit at all times. I discovered it by accident while working in the room with the lights off. Since the sensor is going to be located in a location that is hidden from view and as a result not exposed to direct lighting from the room the sensor is now functioning properly (only turning the LED on when a car is over it). Tom
To the Electronics and DCC Form I have tested my sample of the IR SENSOR OPB742 (Digikey 365-1014-ND), and it is a direct replacement of the QRB1114 IR SENSOR used in my Model Railroader article. The OPB742 has two 0.06” diameter holes. If you completely remove the 0.06” Dia. hole plate over the IR diode, then more IR light will be emitted. You can then reduce the 470K resistor to 220K. Now this IR Sensor REFLECTIVE system becomes less sensitive to any Incandescent lighting in your room, and it still can still detect a black HO Tank car over the IR sensor face. I hope this is the end of the story! Regards to all of you that have built the “Simple Train Detection for Staging Tracks” , you now have a replacement part. You can continue to build more low cost IR train detection well into the future. Robert Frey PE Retired.
Hi Bob
Well I was able to re-try my attempt at wireing the 740 sensor. No LUCK there! I think that the only difference between the 740 and the 742 is that the 742 has the cover or window over the emitter and sensor.
“PROBLEM SOLVED” I hope.
When I arived home last night there was an e-mail from Fairchild that they had shipped me the QRB 1114’s that were not due out for 12 months!
That was very good news for me, and I hope for others too. I love the two led system the best, I believe the price is less expensive than the one led system, penney’s matter when you are doing over 30 of these units plus a bunch more at the club. As you can probably tell, I am using them for more than hidden staging. I am also using them for train tracking/detection. The dispacher is hidden away and needs to know where the trains are. Meets are very important, wrecks are not!
I’ll let you know when and if I really get them.
Thanks again
John
I’ve made this comment before.
MR does a lot of things right, and does them well, but when it comes to electronics, EVERY SINGLE ELECTRONIC CIRCUIT printed in MR during my readership (20 years now) has been wrong. 100%. Some they correct, some they don’t; because of their lag times (which I understand) the corrections don’t appear for two or three months.
I can understand the occasional mistake but their 100% mistake track record is unforgivable. To use the shopworn phrase this is not rocket science.