Another LED constant lighting question for passenger cars . . .

Nice shrink Greg, that's the way to do it.  I did a similar thing after a spell with the Super-Chuffer, I decided that smaller would be easier to fit.  For height, you can sometimes find smaller components with similar ratings, and also use a thinner circuit board.  I did all of those things in this board shrink.

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stan2004 posted:
Rod Stewart posted:

...For grj's new board, I am thinking that since the center rail is the one carrying the DCS signal, the center rail pickups should be connected to pin 2 of the AC input (ie the round hole) since this connector runs through the 22 uH choke. Does that make sense? 

Doesn't matter.  Choke performs same function either way.  

Consider that the board works with 2-rail where DCS "hot" could be either rail depending on car orientation.  

 

 

Stan and John; thanks for this confirmation. Kind of what I figured but thought I would ask anyway.

TEDW; I notice in your pictures the 22 uH chokes you are using are considerably bigger than the ones I wound up with, which are 285 ma. Do you perchance have a current rating for them, and perhaps a P/N? Thanks.

Rod

We are never too old to learn something stupid....

gunrunnerjohn posted:

As long as you have the same number of similar LED's in each car, that will work.  You don't actually need an LED in series with the meter, this is a constant current design, so you can just measure the current with a direct connection across the output.

Ted, the reason mine come assembled is it would take me a LONG time to hand solder a thousand modules!

I hadn't considered this John; great idea. I will likely just do it that way. My head is so engrained with the notion that an ammeter always needs to be in series with the load; couldn't see the forest for the trees.

BTW, that reduction in size of the newer Super-Chuffer board is really impressive. I am thinking the ones I bought a few years ago must be the older style because I recall the pcb material was green. Thinking I should order a couple of the newer ones; do I buy those direct from you, or through Hennings? Too bad the 8 pin DIP couldn't be rotated 90 degrees; that would have allowed even more of a reduction in width by the look of things.

Rod 

We are never too old to learn something stupid....

TEDW; I notice in your pictures the 22 uH chokes you are using are considerably bigger than the ones I wound up with, which are 285 ma. Do you perchance have a current rating for them, and perhaps a P/N? Thanks.

Rod

=======================

Rod, those were sourced from a recommendation for components on the little fixed voltage board I use(pictured earlier in the thread).  Used in this new board cause I had them.  As you see on the invoice they are 560mA.  I don’t know why, just following advice.  I don’t even have DCS, but in the event I do, or the cars are sold, it’s easy to add now and be done with it. They are way pricey from this supplier, I should have ordered offshore.  Hope this helps.  TW

C81153BD-287F-4DAA-9796-5D52CA064FA4

 

 Ted

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TEDW, those don't look too bad at 27.8 cents a piece imo. The ones I got from Digi-Key were 24 cents each and are only 285 ma current rating, about half the 560 ma of yours. Either is ok for these boards of course with the small outputs they have. I think for any future orders I will use the ones you ordered. 

Rod

We are never too old to learn something stupid....

Rod Stewart posted:
gunrunnerjohn posted:

As long as you have the same number of similar LED's in each car, that will work.  You don't actually need an LED in series with the meter, this is a constant current design, so you can just measure the current with a direct connection across the output.

Ted, the reason mine come assembled is it would take me a LONG time to hand solder a thousand modules!

I hadn't considered this John; great idea. I will likely just do it that way. My head is so engrained with the notion that an ammeter always needs to be in series with the load; couldn't see the forest for the trees.

BTW, that reduction in size of the newer Super-Chuffer board is really impressive. I am thinking the ones I bought a few years ago must be the older style because I recall the pcb material was green. Thinking I should order a couple of the newer ones; do I buy those direct from you, or through Hennings? Too bad the 8 pin DIP couldn't be rotated 90 degrees; that would have allowed even more of a reduction in width by the look of things.

Rod 

Rod, Stan does make a good point about the type of ammeter.  The LED is very good at showing you the decay of the light to verify the cap is doing it's job.  You can also put a resistor in parallel with a standard diode to split the load while providing a greater load on the board output for testing.

The S-C board reduction really helped in putting into places it wouldn't fit before.  However, any potential savings by rotating the DIP socket is an optical illusion, the socket measures 10mm in either dimension.  As I've stated previously, the reason for the DIP part is ease of programming.  If I didn't have a removable part, I'd have to provide a programming socket, so there would be no board area savings.  The removable part also makes it easy to do a code change in the field as you don't have to unsolder the board, just pop the new chip in.

Rod Stewart posted:

TEDW, those don't look too bad at 27.8 cents a piece imo. The ones I got from Digi-Key were 24 cents each and are only 285 ma current rating, about half the 560 ma of yours. Either is ok for these boards of course with the small outputs they have. I think for any future orders I will use the ones you ordered. 

Why would you pay that kind of money for a thru-hole choke?  285ma is more than enough for the application, why go bigger for capacity you'll never use?

How about 50 for $1.51, about three cents each?  eBay: 142908355800

Most of the components on the board can be sourced for peanuts if you are patient and wait a few weeks for shipments.

gunrunnerjohn posted:
 
How about 50 for $1.51, about three cents each?  eBay: 142908355800

Those are what I use for thru-hole rolling-stock applications.  Looks like your pads are spaced about 0.4" so here it is on a 0.1" grid project board.  All the listing says is "1/2 Watt" which is an odd way to spec an inductor.  In any case these measure in at about 0.7 Ohms (DCR) so no problem wrt current handling.

22uh ebay inductor 400mil

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"Why would you pay that kind of money for a thru-hole choke?  285ma is more than enough for the application, why go bigger for capacity you'll never use?

How about 50 for $1.51, about three cents each?  eBay: 142908355800"

grj; I was really thinking of possible future applications where the current might exceed the 285 ma. For the constant current LED boards I agree, these are plenty big enough. Gonna go ahead and order some of those that you referenced on the bay, thanks! 

Rod

We are never too old to learn something stupid....

stan2004 posted:
gunrunnerjohn posted:
 
How about 50 for $1.51, about three cents each?  eBay: 142908355800

Those are what I use for thru-hole rolling-stock applications.  Looks like your pads are spaced about 0.4" so here it is on a 0.1" grid project board.  All the listing says is "1/2 Watt" which is an odd way to spec an inductor.  In any case these measure in at about 0.7 Ohms (DCR) so no problem wrt current handling.

22uh ebay inductor 400mil

So check my math on these guys. Based on a resistance of 0.7 ohm, and power limit of 1/2 watt, I am getting a max allowable current of about 837 ma. Sound right? 837 ma across 0.7 ohms give a voltage loss of 0.586 volts, and this times 837 ma = 0.50 watts. Did I get that about right?

If correct, these guys should work for lots of misc. applications, but not engine power pick up of course. For that purpose I use chokes rated at about 3 amps.

Rod

We are never too old to learn something stupid....

You can obviously do that, though for three cents, I'd put in the choke in case the cars find their way on a "guest" layout.

At half the 837 ma current (ie. 420 ma approx.) across the inductor suggested by Stan, I get about 1/8 watt power dissipated. Whereas a current of 600 ma gives approx. 1/4 watt, ie half the rated power. So the power dissipated actually varies as the square of the current increase. Might be over-thinking it I suppose. 

Rod

We are never too old to learn something stupid....

You're right, of course, I just divided by two.  I should have thought about it.  In any case, I'd limit my planned power dissipation to around half the rated capacity.

Patrick1544 posted:

John

If I want to order your board and use it with TMCC operations only, do I eliminate the choke and put a jumper in its place?

Or, for 3 cents each, DigiKey will sell you 0 Ohm resistors  

https://www.digikey.com/produc...4ZT0R00CT-ND/1830304

 

gunrunnerjohn posted:

You can obviously do that, though for three cents, I'd put in the choke in case the cars find their way on a "guest" layout.

What he said.  Just think of it as a 0.7 Ohm resistor which in this context is the same as a jumper! 

gunrunnerjohn posted:

You're right, of course, I just divided by two.  I should have thought about it.  In any case, I'd limit my planned power dissipation to around half the rated capacity.

Got it. Good advice!  It's hurting my head thinking about it.

I actually confirmed it using Ohm's Law:      V=I * R  and   W=I * V

                                    So substituting:    W= I*(I * R),    or  W = (I)^2 * R

                                    Re-arranging:       I^2 = W/R       or  I = (W/R)^.5

Now if you use W = 0.25 watt and R = 0.7 ohm; I works out to 597 ma, or call it 600 ma for simplicity.

Whew, time for a gin and tonic! 

Rod

We are never too old to learn something stupid....

So, FWIW, with all the high end computations being put forth(SNL’s Chevy Chase said, "It was my understanding that there would be no math.") here is the price breakdown on the lighting pcb, sans labor, for my assembly.  The parts were US sourced, so we all realize savings can be achieved with off shore sourcing. YMMV

854BA060-0177-4CC6-A4BC-5C076A24EE39

 Ted

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Ted, I am sure I am well over the total you listed for my lighting boards but at this point I am happy with the way they are turning out.  Like you, I usually source my parts from the US but that may (probably not but never say never) change since DigiKey's minimum shipping is now $4.57 for less than eight ounces using USPS.

I have enough parts for 15 boards (need to order more boards) that should be sufficient to upgrade the highest priority cars.  After that maybe order enough for 25 more cars.  Not sure I have 40 passenger cars but there are many cabooses I could upgrade someday.

Greg

Greg, I think you are being too modest in your ability.  Designing and producing your own pcb was no small feat it seems to me.  Certainly not something I would tackle even for an experiment.  Cost may be one factor, but you should take no small amount of satifaction in your first successful attempt at building the module.  It is a fun part of the hobby to put these little projects together, and they actually work!  That little fixed voltage module I pictured earlier can be made for a $1.10!! 

 Ted

Ted/Greg, I think both of your projects have come along really well, and provided others with ideas for moving forward. My cost per module may be a little lower, mainly because I went offshore for the pots and the LM317T's. But on the other hand, you both already have operating modules, whereas I am still waiting! Haha. 

gunrunnerjohn; do you have any further info for that board supplier where you said it looked like they could be had for around 20 cents a copy? I will need to order more boards at some point, and fast delivery is not especially important. Can they run with your Gerber zip file as is?

Thanks, Rod

We are never too old to learn something stupid....

TedW posted:

So, FWIW, with all the high end computations being put forth(SNL’s Chevy Chase said, "It was my understanding that there would be no math.") here is the price breakdown on the lighting pcb, sans labor, for my assembly.  The parts were US sourced, so we all realize savings can be achieved with off shore sourcing. YMMV

So I am not providing anything "new" here, but it occurs to me that someone stumbling on this thread next month or whenever might be looking for a summary on exactly what/where to buy.  As I see it, there are 3 orders:

1. Bare boards from OSH Park using GRJ's link earlier (I can't seem to consolidate reply-with-quote from previous thread pages) so duplicating the link here:   https://oshpark.com/shared_projects/mMzHpYbk

$3.80 for 3 boards ($1.26/board) shipping included.  You will need to create an account.

2. Components.  I used TedW's DigiKey cart link from earlier and updated it to include the 22uH choke/inductor listed in the parts list (BOM) from GRJ's OSH Park link. https://www.digikey.com/short/p3mr70

I also notice you can select a "photo" view of a DigiKey cart:

dk cart

I entered quantity 25 for all the components.  So with new 2019 USPS shipping rates, the total with shipping would be about $71.  Or $2.85 per board.  You don't need to set up an account.  As TedW says, you can get this down to about $1 per board if you do eBay or similar.

3. LED strip.  Numerous OGR threads on options.  When you buy a "standard" 5-meter reel which is what you'd do for 25 cars, you'll end up spending a few pennies per LED or, say, 50 cents per car.

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In the interests of consolidation, here's all the files and information necessary to build the unit and order boards from anywhere you like.  Gerber files, BOM, schmatic, and even a 3D representation of the board.

Pass_Car_Lighting thru-hole Gerber Files.zip

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