BigRusty,
The Sharp IS471 chip can only output about 50ma which is too low for most ordinary relays.
The 555 chip can handle up to 200ma which makes it much easier to work with. I took a look around and found these relays on the allelectronics.com website for $4 apiece that seem to be in the ballpark. I have ordered stuff from this company and they are usually reliable. I have not tried these relays so some experimentation would be a good idea before doing a big order.
When connecting a 555 chip to a relay, you must use a diode to protect the chip from the back EMF that you get when the power is removed from the relay. This web site has some useful information on this topic.
Years ago as a when I was in high school, I used to build a lot of electronic projects, many of them using the 555 chip. Brings back happy memories.
Anand
Slowly building a layout since 2007!
You can make a monostable easily and inexpensively with a 555 chip and a few components. I found this circuit for example: http://www.doctronics.co.uk/555.htm#monostable .
The other advantage is that this monostable circuit can directly drive a small relay. The output from my IR detector is too feeble to directly drive a relay.
Thank you from me also Anand.
I didn't realize that the IR detector output was so feeble.
Can anyone recommend an inexpensive relay that will operate with the Mononstable circuit output. I need 3PDT relays because I also interupt power to a stopping section before each signal to prevent rear end collisions.
In my opinion this is really the only practical solution to signalling using DC on a large layout. If I don't use the stopping section there would be no need to gap the rails. Only one rail is needed to do that.
Hi,
thank you Anand, you just solved a problem for me as well with your link to the monostable circuit.
Frank
"If you need a helping hand, you'll find one at the end of your arm."
BigRusty By installing three detectors in a block any one of them would be closing that blocks relay, thus changing the signal to red. As a train occupies Block A that signal turns from green to red. If any part of the train still occupies block B, the signal would also be red. With twin T it would be yellow because there are no resistors on the cars wheels. If any part of the train also occupied Block C that signal would also be red, with twin T it would be green. The signal for block D would be yellow, because the relay for block C changes the green to yellow. The signal for Block E would be green of course. This could probably done with just a detector at the beginning and end of each block. This would far less expensive than installling wheel resistors on several hundred pieces of rolling stock which is required by any track detection device, not to mention the time saved in not having to do that.
By installing three detectors in a block any one of them would be closing that blocks relay, thus changing the signal to red. As a train occupies Block A that signal turns from green to red. If any part of the train still occupies block B, the signal would also be red. With twin T it would be yellow because there are no resistors on the cars wheels. If any part of the train also occupied Block C that signal would also be red, with twin T it would be green. The signal for block D would be yellow, because the relay for block C changes the green to yellow. The signal for Block E would be green of course.
This could probably done with just a detector at the beginning and end of each block. This would far less expensive than installling wheel resistors on several hundred pieces of rolling stock which is required by any track detection device, not to mention the time saved in not having to do that.
The only thing I would suggest is that you use a monostable along with the detector to stretch out the signal from a detector and act as a debounce mechanism. Note that when a train is passing over an IR detector, it will "chatter" due to the gaps between the cars. By using a monostable, you can get it to ignore these gaps and stay triggered continuously while the train is passing over the sensor.
Rangachari Anand
Sorry, I mst have not made myself clear. First, I am operating in DC not DCC. Second, I have no intention of operating by computer. Third there is no need for a computor. Forth, I operate long freight trains, upwards of 50 cars and sometimes 75 cars. My blocks are 10 feet long, so a train can cover several blocks.
Cheap relays are all that is needed, one for each block. The relay changes the following signal from green to yellow if it is closed to light the red signal on its own block. The only wiring necessary is from one relay to the following one to accomplish that. It worked for years on my previous layouts.
Since detectors are needed regardless of what method is used, this a far less expensive alternative than using a computer. If you plan to control your trains with a computer, the same system could tell the computer where every train is and what blocks it is occupying in greater detail.
BigRustyBy using infra red detectors wired in parallel for each signal block, all of the blocks occupied would all be showing red. In other words there would be a detector at the beginning and end of each block with perhaps one or two in the middle to be sure that the red signal does not clear until all cars have cleared the block. Has anyone tried this?
By using infra red detectors wired in parallel for each signal block, all of the blocks occupied would all be showing red. In other words there would be a detector at the beginning and end of each block with perhaps one or two in the middle to be sure that the red signal does not clear until all cars have cleared the block.
Has anyone tried this?
This could work provided you are willing to install a lot of detectors and use a computer to integrate the signals from all those detectors. As you say, for each block, you would need several sensors. I think it may get expensive even if you use my low-cost sensors since you would need so many of them. I would suggest you stick with the current draw detection approach for this purpose. Many DCC manufacturers offer reasonably priced current draw detectors.
My situation is a little different since I use my computer to actually control trains on my layout. In order for this to work, the computer needs to know when a train reaches a particular point on the track. IR detectors are perfectly suited to this application. My software knows which sensor will get triggered next by the movement of a train and waits for that sensor to get triggered.
Your right, my mistake - sorry Rangachari. Sometimes the old fingers and brain don't work too well together...
In my last three layouts I used the NMRA twin T detectors coupled with relays that cleared the green signal to red when the block became occupied and overode the following green to yellow. This worked perfectly except for trains longer than the block unless I put resistors on all of the wheelsets.
For my new layout in planning, I am considering using shorter blocks, including passenger stations with multiple tracks.
Robert Beaty
The Laughing Hippie
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The CF-7...a waste of a perfectly good F-unit!
Then it comes to be that the soothing light at the
end of your tunnel, Was just a freight train coming
your way. -Metallica, No Leaf Clover
Robert, Very nice work on your detector design/circuit and documentation.
I used the ones I did because they were integrated on a board that did signal animation. My layout is in a low light room and I like to operate in a night scene, so infrared has worked out well.
rxanandI have come up with my own low-cost IR detector that I have described in this article on my web site: http://coralfringe.com/IRDetection.html
I have come up with my own low-cost IR detector that I have described in this article on my web site: http://coralfringe.com/IRDetection.html
Made that link clickable.
I went the same route - I tried out the Micro-mark IR detectors. It works well but cost is too high. I have come up with my own low-cost IR detector that I have described in this article on my web site: http://coralfringe.com/IRDetection.html
My IR detector works perfectly with feedback decoders like the TC-64 from RR-CirKits.
I am currently building a batch of these detectors for myself and a friend (100 in all). At these quantities, the cost is just about $2.50 per sensor.
The big advantages of this approach over Rob's circuits are:
1. Very resistant to triggering on spurious signals since the chip uses a sophisticated circuit to eliminate stray IR.
2. Easy to build since it requires just two components, the Sharp IS471 chip and an IR LED (I use the Fairchild QEC113).
Rob does indeed have some great circuit designs and kits on his site. I built his across-the-tracks IR detector circuit and crossing bell circuit, and they work great for the grade crossing crossbucks.
Rob's between-the-rails IR detectors should work great under HO scale track but they are too large to "look-up" between N scale ties - at least that's what he said.
I can vouch for Frank’s suggestion to build Rob’s circuits from his site. I have purchased two of Rob’s circuit boards for his photocell detectors and built the detectors. They work great and were very inexpensive compared to commercially available products.. Top notch quality….Hopefully there is something at the site that you can use...
Guy
see stuff at: the Willoughby Line Site
Hello,
here is a web site with lots of interesting electronic projects. One of them is an Infrared Detection system. The site is http://home.cogeco.ca/~rpaisley4/ATDetIR.html .
I hope it helps.
http://chartiers.50webs.com/project4.htm
p.s. I believe Micro-Mark imports their IRDOT detectors from Heathcote Electronics.
Has anyone used these products? I have Logic Rail signal controllers that use photo cells. However they can't be used in a night time environment and I have bad lighting for photo cell use. These infra red detectors are compatible with Logic Rail but can break the bank at about $30.00 a pop. The price you pay for realism....