A Handy Little PCB for Adding Marker LEDs to a Hood Diesel

Rod, a key element missing is the schematic of the board, that would be very useful to folks looking to fit this into an application.

Bravo....Rod I almost missed this. I can use this board on several projects. Much neater than tedious in line resistor, diode and shrink wrap method. Many thanks for sharing. 

Richard

So here is the circuit as requested. Not very complicated haha!

Rod

@Rppoind posted:

Much neater than tedious in line resistor, diode and shrink wrap method. Many thanks for sharing.

Richard

Richard; exactly why I decided it was needed!

Rod

Ditto what @Rppoind said.  I also have some projects where these could be used.

Also, I highly recommend reading @Rod Stewart's attached notes in his first post; they are loaded with great information and details about the applications and installations for this board--a trove of useful info.

THANK YOU, Rod.

NOTE:  Just ordered your board from OSH Park  priced at $2.40 for 3 with free shipping; ordered 6 for $4.80.

What would be cool is to run both forward and reverse lighting to the board and then make it a bi-color LED that changes color with the locomotive direction.   You could also add headlight outputs that would just have pigtails to connect one or two headlight LED's.  To really Gild the Lily, you could also add number board LED outputs that would light anytime either forward or reverse lights were on.

I'm going to beat you to saying this...

Nothing is so easy as the job you imagine someone else doing!

Would a diode bridge rectifier at the input help with LED flicker for AC power sources?

A capacitor would also be a major help with flicker.

@A. Wells posted:

Would a diode bridge rectifier at the input help with LED flicker for AC power sources?

A bridge diode would be better of course, but larger; as would a 47uF cap or similar, as suggested by grj. But to me an led flickering at 30 Hz is not noticable at all. Maybe it's just my tired old eyeballs? And the more jewellery you add the bigger the board becomes; I wanted something simple and compact. You often don't have a lot of room to work with.

Rod

@Rod Stewart posted:

You often don't have a lot of room to work with.

Think surface mount.

@Rod Stewart posted:

A bridge diode would be better of course, but larger; as would a 47uF cap or similar, as suggested by grj. But to me an led flickering at 30 Hz is not noticable at all. Maybe it's just my tired old eyeballs? And the more jewellery you add the bigger the board becomes; I wanted something simple and compact. You often don't have a lot of room to work with.

Rod

There looks to be a lot of room on the back of that board for a thru-hole bridge diode rectifier in my opinion.  I was also going to recommend adding a capacitor to the output of the rectifier as well.

Actually, you could hook a separate small diode bridge rectifier based board up pre marker LED PCB.  So no worries on space requirements on the PCB.  And, if you really, really want a small AC to DC rectifier, you can always tear one out of a Lionel FasTrack Remote/Command Switch.

You really advocating destroying a $100 switch for a fifty cent part?

In answer to the potential half wave AC flicker issue, I whipped up a fast SMD re-design with a bridge diode, 47uF cap, and a 1210 size load resistor R1. It worked out quite well, and the board stays the same nice compact size. Here she be:

The little bridge diode is an SOT-123 size (good for 200ma) and would be the most challenging part to solder. I just happen to have a few of these in stock, so that's handy, same for the little caps. The 1210 size resistor is easy to solder, and the size means it is good for 1/4 watt. You can also use as small as an 0805 size with the same board pattern, but it will be only 1/8 watt. Note that depending on the circumstances you could install the leds through from the other side of the board just as easily. The three smd parts though have to stay on this side of the board because, well, they are surface mount.

This board would eliminate any potential AC flicker, real or imagined,  and also would help with any center rail voltage dropouts. I wish I had other boards to order right now so I could add a few of these to it. But my latest board order just shipped today already. Drat, bad timing. Might look at getting a batch of assembled boards done with a load resistor sized for 18vac track power. It can easily be changed if needed.

Rod

@Pingman posted:

Ditto what @Rppoind said.  I also have some projects where these could be used.

Also, I highly recommend reading @Rod Stewart's attached notes in his first post; they are loaded with great information and details about the applications and installations for this board--a trove of useful info.

THANK YOU, Rod.

NOTE:  Just ordered your board from OSH Park  priced at $2.40 for 3 with free shipping; ordered 6 for $4.80.

Thanks for that recommendation.  I ordered 6 as well and thanks Rod for posting it.

John

FWIW, I built up a test board using a 1N4148 diode and a 620R resistor with two green 2mm post leds. It works just fine at 18VAC track power, and I don't notice any flicker whatsoever. So I think the half wave diode rectification is really all you need. And it would be cheaper and easier to build than the smd variant I posted above. But for those who are worried the smd board should alleviate all issues.

As a matter of interest various manufacturers including K-Line used to connect engine marker leds directly to 18VAC track power, using a 1K resistor in series with two opposed 1.8mm leds (cathode to cathode). Worked just fine. Each led would be operating at 30 Hz, one on the positive voltage swing and the other on the negative swing, each at about 13ma.

Rod

Nice work!

@Rod Stewart, just received email today from OSH Park that the six boards I ordered were shipped.

Thanks, again.

I had a request from a gentleman wanting the bridge rectifier version, so I decided to add the files needed for anyone who wants to go this route. I had to update the rectifier  because the original I used is now out of stock, with no expected re-stocking date. The new part is a little bigger so the board width had to increase slightly to just under 10mm. No big deal.

Note that the 1210 smd resistor will  need to be selected for the AC voltage you will be using, and should be about 1.4 times the value of the part shown in the original user notes in the OP. So for instance, if you are using 18VAC (instead of DC) and green leds @13ma, the value should be 1.2K x 1.4 = 1.68K; rounded up to 1.8K. Purchase this value in lieu of the 330 ohm shown in the BOM below.

The circuit is the same as shown five posts above. The board layout, 3D view, Digikey BOM and the gerbers are included below.

Note that the Digikey prices shown in the BOM are for lots of 10 each of the parts, and are Canadian dollars. US prices will be about 75% of these. Hope this helps for anyone wanting to go the rectifed AC route.

Rod

Got my boards from OSH Park yesterday.   The original one shown in this thread.

Thanks,

John

@Rod Stewart posted:

As a matter of interest various manufacturers including K-Line used to connect engine marker leds directly to 18VAC track power, using a 1K resistor in series with two opposed 1.8mm leds (cathode to cathode). Worked just fine. Each led would be operating at 30 Hz, one on the positive voltage swing and the other on the negative swing, each at about 13ma.

Rod

I am surprised no one caught this. I got to thinking about it and suddenly realized that if two leds were wired in this manner, they would effectively block each other, and no current would flow. I tested this on the breadboard and sure enough! Reversing either one of course instantly set things right and all was well. I must have misinterpreted the circuit years ago when examining one of these in a K-Line Mikado or whatever it was. And I assumed it was correct all this time. Sorry about that!

Rod

Well, actually connecting them in parallel with anode to cathode on each side would do what you describe, and is a recognized way of allowing the one LED to protect the other one from excess reverse voltage.  After all, they are Light Emitting Diodes!  The emphasis is on diode, the conducting diode prevents the reverse voltage from rising above the fairly low reverse voltage specification of the LED, typically from 5 to 7 volts.

@Rod Stewart posted:

I am surprised no one caught this. I got to thinking about it and suddenly realized that if two leds were wired in this manner, they would effectively block each other, and no current would flow. I tested this on the breadboard and sure enough! Reversing either one of course instantly set things right and all was well. I must have misinterpreted the circuit years ago when examining one of these in a K-Line Mikado or whatever it was. And I assumed it was correct all this time. Sorry about that!

Rod

Hi Rod,

I have six of these circuit boards.  Can you be a little more specific as to what I should wire to what to use them?  I am not following the exception.

Thanks,

John

John, you can wire the board to any onboard AC or DC source that you wish. Just select the appropriate load resistor value from the user notes table and you should be good. If you are using AC you should probably install a blocking diode D1 on the board where shown, and use a lower value resistor as suggested in the notes.

If you can tell us more about your supply source, I can give you more specific info.

Rod

@Rod Stewart posted:

John, you can wire the board to any onboard AC or DC source that you wish. Just select the appropriate load resistor value from the user notes table and you should be good. If you are using AC you should probably install a blocking diode D1 on the board where shown, and use a lower value resistor as suggested in the notes.

If you can tell us more about your supply source, I can give you more specific info.

Rod

My supply source is a Lionel KW transformer running conventional.

Thanks Rod,

John

Ok so assuming that the board will be wired directly to the track rollers, and in conventional you are not liable to exceed perhaps 12VAC to the track, you should use the blocker diode D1 as discussed, and R1 should be about 280 ohms for led currents in the range of 10-13 ma.

Hopefully that helps?

Rod

The blocker diode can be a 1N4148 or 1N4002/1N4003 or anything similar. No magic to it.

Rod

That's extremely helpful Rod.

Thank you so much.

John

Just bumping this topic to the front page so that rtr12 can add it to the electronic projects master list file.

Given that the boards are $.80 each at OSHPark, total cost shouldn't be more than $2.00 each, to as low as $1.00 for all offshore components.

Rod

Take a look, got it added. Let me know if I need to fix anything and I'll get it corrected.

Looks good rtr12. There is actually two boards in the thread. The first one is simple designed for dc power, and the later smd version which is good for ac track power.

Rod

Did some editing to account for the R2.1 board (fixed the picture too). Hopefully I didn't butcher the description too badly.

Should have read the thread a bit closer, I was thinking the R2 version had evolved and replaced the R1 version. Pays to read the whole thread instead of just skimming the text and looking at the pictures! 

Looks good rtr12!

Rod

@Rod Stewart posted:

A bridge diode would be better of course, but larger; as would a 47uF cap or similar, as suggested by grj. But to me an led flickering at 30 Hz is not noticable at all.Maybe it's just my tired old eyeballs? And the more jewellery you add the bigger the board becomes; I wanted something simple and compact. You often don't have a lot of room to work with.

Rod

The flickering is why your eyeballs are tired.            j