Insulated Rail Relay Based Sensor

I finally figured out how to set up individual relays and you have to go and make something simple.  For those using Command, while John is setting these up to draw track power I like to use AUX 14 volts to power the relay(s) and signals.  The reason being I sometimes forgot to shut down the layout, having all of the signals lite up is a visual que to me to shut things off before going to sleep.  Also, if I have an un-powered but occupied section of track (hidden return loop) I don't want any surprises when I power up that section.  A red signal is a sure sign that something is under there.  

Henry

clem k posted:

I have never done isolated rail thing, how long does the isolated rail have to be and how far from the grade crossing protection can it be ? Also will this work with Z Stuff?

The insulated rail can be any length, and it can also be in any position.  It really depends on what you're using the signal capability for.  We have some on the club modular layout that are 20-25 feet long or more, they protect a couple of long tunnels that otherwise we could have issues if someone stops or gets stuck in there.  There's a signal at the entrance, and right past the signal, the insulated rail starts until the tunnel exit  We have some insulated rails that are shorter and are for crossing signals.

rtr12 posted:

Probably just a try would be sufficient for me, don't think I would want a steady diet of SMT to assemble. Sending those out sounds like a good plan to me. I am amazed at how small things can be made with SMT.

 Yep, I only assemble what I need for prototypes or small low count projects.  I also have learned quite a bit about laying out a design for easier hand assembly.  Positioning the parts for easy soldering, and also picking sizes that are reasonably easy to handle are key.  I did one design early on and I specified a size 0201 resistor!  I don't don't know if you realize how small a 0201 resistor really is!  Check the table below!  I couldn't even see to position it using my desk magnifier, and forget about soldering it!  I've since set a self-imposed lower limit of 0603 parts with a preference for 0805 or larger.  I also steer clear of any multi-pin part at a spacing of less then about .095mm between pins.

rtr12 posted:

I think the time delay suggestion above might open the door for another module, but I think you are right to keep these simple and as they are. I think there would be many more users that way. You could add the time delay, larger relays, flashers or whatever in separate modules later if the demand is there. A modular system so to speak. 

 There's always room for a future product that does much more.  If I went that route, I'd probably consider a uP based project to give me a lot of flexibility.  A uP with a nice big jumper field for options would provide lots of flexibility, but it would also carry a higher price tag.  There are always tradeoffs...

Oh goody.  Now I don't have to use your LED lighting module to control a 99 cent eBay relay module for insulated rail sensing!   Now it's all on 1 board!     Video of GRJ's LED board drafted for insulated rail duty in this post.

Looking good GRJ!   BTW take a look at R1 for 14V Aux power operation.  If using the HK19 relay with 400 ohm coil that 620 ohm divider may not provide the minimum 9V spec to trip the 12V relay.

Not sure how many applications need the 2nd pole but just wondering about mixing the 6-position terminal screw strip connector with a 3-pin header.  For the average guy those 0.1" square-pin sockets are a nuisance if you don't have the crimp tool, soldering iron, whatever.

Also, in the creeping-features category, as mentioned earlier one sometimes useful feature of ITADs is the settable time-delay.  Like that optional SMT diode you tossed in for coil flyback (I concur it's not needed), I'm "imagining" a 50 cent optional SMT circuit to insert a settable time-delay.  Would require continuous power so would add another terminal to "ground" (outer-rail).

The three pin header was just to allow use of the second set of contacts.  My feeling was that a vast majority of the users would not need or use them.  The resistor is indeed sized for 18 volts, for a lower voltage, the resistor would also be changed in value.  I suppose I could leave that one unsoldered and include a couple of choices in the package for various input voltages.

Stan, I thought about an "enhanced" model, but I've found this to be pretty useful in our own setting, so I figured I'd float this one first.

I just realized I didn't address the last part of your comment Stan.  I'm using the HK19F-DC12-SH2C with the 720 ohm coil.

Holy mackerel, those 0201 items are only .001" x .002" according to the Google mm to inch calculator. That is TINY! I wouldn't want to try one of those, I will take your advice on that one and stick to the 0603 minimum. I think those little square chips with lots of little tiny fingers on all four sides would be pretty ugly as well. It's amazing they can get the robots to do that stuff. Probably have to pay them more, TINY duty pay. 

I guess on the good side those would certainly allow some very small PCBs.

rtr12 posted:

Holy mackerel, those 0201 items are only .001" x .002" according to the Google mm to inch calculator. That is TINY! I wouldn't want to try one of those, I will take your advice on that one and stick to the 0603 minimum. I think those little square chips with lots of little tiny fingers on all four sides would be pretty ugly as well. It's amazing they can get the robots to do that stuff. Probably have to pay them more, TINY duty pay. 

I guess on the good side those would certainly allow some very small PCBs.

You read that wrong. 0201 is .024 x .012. Inches!

Thats still big. We use 01005 in cochlear implants at work. Thats .016 x .008. There is now a size smaller!

We have to use solder stencils that are .003 etched stainless so that the solder paste isn't higher than the part. 

Lou N

A bit off topic of the thread, but he entire process of using solder paste and pick and place machines is completely fascinating to me.  Here's a good walk-through of the process used for machine-assembled boards: 

For anyone that is interested in electronics, btw, the EEVblog is a wonderful youtube channel with countless hours of content on all aspects of electronics, including basic components and theory, product tear-downs, in-depth theory, and BS-gadget-debunking.  Oh and in case anyone's interested, the circuit being built in the above video is a device that allows more accurate current reading at micro and milli amps when using a digital multi-meter.  

JGL

John,  great idea!  I built several relays using a design that was published in CTT several years ago,  the parts were available from Radio Shack,  your design would be a big upgrade and easier to use.  Since the Radio Shacks near me are no longer, sourcing parts are not easy either.  I like the idea of having kits available for those that need several.

Best wishes,  Dave

JohnGaltLine posted:

A bit off topic of the thread, but he entire process of using solder paste and pick and place machines is completely fascinating to me.

JGL

Those are big parts and really slow machines.  But it demonstrates whats happening. 

Let me know if you ever come to cleveland. I'll show you machines that put down 17000 parts an hour. 

I work here:  www.valtronic.com

Lou N

Hey John,

Great idea to provide this feature in a plug-n-play (of sorts) module. To keep cost down, could you use one of the many 2-relay modules from the bay, which already have LED's, isolation, CONNECTORS (!) and are priced at a little over a dollar ($1.10, $1.35 . . )?

Like this one - and just add your smaller board with a few components and a two-screw terminal block

Good luck and keep us posted.

Alex

Lou N posted:

rtr12 posted:

Holy mackerel, those 0201 items are only .001" x .002" according to the Google mm to inch calculator. That is TINY! I wouldn't want to try one of those, I will take your advice on that one and stick to the 0603 minimum. I think those little square chips with lots of little tiny fingers on all four sides would be pretty ugly as well. It's amazing they can get the robots to do that stuff. Probably have to pay them more, TINY duty pay. 

I guess on the good side those would certainly allow some very small PCBs.

You read that wrong. 0201 is .024 x .012. Inches!

Thats still big. We use 01005 in cochlear implants at work. Thats .016 x .008. There is now a size smaller!

We have to use solder stencils that are .003 etched stainless so that the solder paste isn't higher than the part. 

Lou N

Thanks. You are right, I entered .06 & .03 mm instead of 0.6 & 0.3, was looking right at GRJ's chart when I did it too...duh. I thought that was awfully small.  Those implant parts really are small! I saw some automated PCB manufacturing in the late '80s. Boards were much larger and so were the parts, but still impressive. I can only imagine what they have now. I am going to watch JGL's video to find out.

GRJ,

Would an LED across the relay coil be something that might be wanted, to monitor status? Would probably take up more room and may not be worth the extra space, cost, ruining the design, etc.  Just a thought.

GRJ,

If and when, please count me in for three or four.  Another great idea.

Tons of stuff you could add to it, but I have to stop somewhere.  

I know that there are smaller parts, but when you're trying to put something together with tweezers and a soldering iron, the 0201 is 99% impossible, and smaller stuff gets to 100% impossible.   I find that 0603 and larger are fairly easy to deal by hand.  I'm getting to be an old fart as well, so maybe someone with 22 year old eyes and rock steady hands might be able to use the smaller parts, I'll leave it to such folks to try.

Alex, I've done things that depend on eBay products, but it seems I frequently get burned as they fade out and aren't available anymore.  I'm depending on such modules less and less and sticking to parts that I should be able to source for the foreseeable future.

John,

I agree. I have bought a number of 'modules' of different types from the bay, and when I have gone back for more, the same one I bought may no be available, but a similar one is. I understand how this may be a problem for any sort of production runs that me be done at different times vs just one single run.

Alex

John, I'm pretty ignorant as to exactly what your board can or can't do.   Presently I am using  one outside rail for a common and the other is isolated for signal detection.  If I make both outside rails common, can I use this board to detect train presence?

Art

Ingeniero No1 posted:

I agree. I have bought a number of 'modules' of different types from the bay, and when I have gone back for more, the same one I bought may no be available, but a similar one is. I understand how this may be a problem for any sort of production runs that me be done at different times vs just one single run.

Exactly.  If you're just creating a one-time solution, then the eBay modules are certainly the way to go as they're dirt cheap, far cheaper than I could ever do similar functionality.

Chugman posted:

John, I'm pretty ignorant as to exactly what your board can or can't do.   Presently I am using  one outside rail for a common and the other is isolated for signal detection.  If I make both outside rails common, can I use this board to detect train presence?

Nope, it uses the insulated rail.  The board is very simple, it's just there to eliminate any chatter and also provide totally isolated and sets of contacts to operate signals and accessories.

I did some "thinking" and a brief bench test of my design and came up with a couple of improvements.  I decided to add a low value resistor and the cap, then the larger resistor to drop the voltage for the relay coil.  This allows the capacitor to charge much quicker, and the 100 ohm resistor limits the inrush current to avoid arcing at the wheels.  The capacitor also has a higher voltage so that it has a larger delay before allowing the relay to drop out.  I also used more reasonable sizes for the discrete components and changed the relay flyback diode into a thru-hole part since there was room to do so.

Looking good. I'm in for a few.

Sounds like some good improvements. Where do I place my order? 

Still waiting for my parts to come in so I can check for fit and get a quantity of boards.

Great John! This is way better than what I rigged up.  I will swap mine out for yours.

George

If using the aux power supply option, what is the lowest voltage that would work? 

I'm giving thought to leaving out the one resistor and including a couple different values in the package, so you can "tune" it for the voltage you have.  Being a thru-hole design, it's simple for most anyone to solder the correct value resistor into place for the specific voltage you're running the relay coil at.  Obviously, I don't care what voltage you use on the relay contacts.  The values in the schematic are good for 16-22 volts AC on the track, but if you had 12 VAC, you'd probably want a lower value resistor.

I'm hoping the Chinese get my terminal strips and relays here so I can put a couple together.

I like it John. I'm always playing with relays so there is bound to be a use come up for one sooner or later.  Put me on your e-mail list and I will probably buy a few from you, as long as the price is reasonable of course.

RRmarioE@comcast.net

I'm determined to keep it under $100 Mario.

Count me in for a couple.

gunrunnerjohn posted:

I'm giving thought to leaving out the one resistor and including a couple different values in the package, so you can "tune" it for the voltage you have.  Being a thru-hole design, it's simple for most anyone to solder the correct value resistor into place for the specific voltage you're running the relay coil at.  Obviously, I don't care what voltage you use on the relay contacts.  The values in the schematic are good for 16-22 volts AC on the track, but if you had 12 VAC, you'd probably want a lower value resistor.

I'm hoping the Chinese get my terminal strips and relays here so I can put a couple together.

Well, let's see, 12 volts divided by 720 ohms is about 17 mA.

Why don't you just feed the coil with a CL2 at 20mA and it will adjust itself!

PLCProf probably has a much better idea (I didn't know where the CL2 would go?), but I was thinking of maybe having both resistors with a jumper to switch between them for the different voltages desired, like high or low (resistors are a little easier than the CL2, more my speed).

After looking at the maximized use of space on the board, I imagine that would probably make the board bigger and wouldn't be so desirable? Anyway, just a thought, but I defer to you and PLCProf (and Stan if he stops by).

As a card-carrying member of the Peanut Gallery, I concur with PLCProf's idea of the board taking care of the voltage difference.  I think the CL2 is a sole-sourced component so I'd go with a voltage regulator rather than a current regulator using, say, the widely available 78L12 12V regulator (10 cents) which is half the cost of the CL2.  I don't know what percentage of customers would run this with 18V AC command voltage vs. 14V AC aux/acc voltage vs. 12V DC...but I think shipping multiple resistors is a logistical rabbit-hole.  But it's GRJ's party and it's rude to insult the host! 

Actually, the peanut gallery is curious about the Ground terminal that presumably connects (optionally) to track outer-rail Ground...but then goes nowhere (N/C) on the board. 

I like the CL2 or regulator idea, it simply never occurred to me!  This is why I post, someone always comes up with a great idea at the last minute  Since I only ordered a couple of prototype boards, I think I'll make the change.  Thinking about it, Stan's idea of the regulator is probably a bit cheaper, something to be said for that.  FWIW, since I'll have to wait for boards anyway, the 78L12 is only a little over 3 cents shipped from Hong Kong.  The regulator should allow operation down to 9-10 volts AC, the low current draw of the relay will allow the cap to charge close to peak voltage.  Ding...ding...ding... we have a winner!   I'll still leave a small resistor in front to limit the inrush current, maybe cut it down a bit, 47 ohms or so.

The ground terminal is really just to allow you  to have a junction point.  I had given some thought to a .1" jumper that would connect the ground to the common of one set of relay contacts, but I didn't do it.  That would probably make it more useful.  Let me mull that one over...

Here's what the "new" mods look like.  I added the regulator and the jumper to ground the common of the relay as an option.

Just waiting on the terminal strips to come from China so I can do a trial fit and insure the layout is good.  When that happens, I'll order a batch of boards.

I did add a couple of options, might as well while it's still only on paper.

I expanded the ground center common to ground or power to the common of the #1 set of relay contacts.  If you want to power something like an LED signal directly, you don't need any aux power, just use track power with a diode and resistor.

I also added an off-board expansion capability for the capacitor.  This will allow you to extend the time the relay stays closed after the train leaves the insulated rail.  I got to thinking that maybe someone would want a longer delay...

I'm still following along here. Sounds like some more good additions to the project and not too difficult for folks to use. 

I am glad you say that RTR, I will be bothering you when the time comes! LOL

Certainly in concept it's pretty simple.  It was too simple, so I added a few options to obfuscate it.

LOL way to go John, I think your just making it so I keep reading. But then again I would any ways cause its the only way I am going to learn.

GRJ, if the price is in the $10+/- ball park, put me down for 2 or 3, plaease.

Mike, I think in this case I would bypass the middleman (me) and go directly to the source (GRJ). You'd probably get much better (and correct) answers that way.   Nothing beats talking directly to the design engineer!

That's the goal.  I have all the parts except for the terminal strip, I'm using the Euro style terminal blocks.  In order to keep the price of parts reasonable, I ordered a bunch of these from China, they're not here yet.  All the other parts are in.  I want to get the terminal blocks and verify fit for sure before I order 100 or more boards, it would really bum me out to have another fiasco like the WD Generator issue where I had to scrap the first batch of boards because I was in a hurry to get them.