An Easy To Build DIY Trackside Crossing Signal Flasher Module, with Gerbers

Rod: Nice work! Where's the video?

Rod, I know this little board will be very useful for a lot of members.  Thanks very much for all your time and effort.  And, squeaked under a dollar per unit from off shore.  👍😏

Rod

Great work! You put a lot of work into both the circuit and the instructions making it simple to build.  There is a huge cost savings in building your own circuit.  Two model train circuit manufacturers supply similar circuits retailing at $14.95 and $19.95.

One comment on hooking up LEDs to your circuit.  If you want to use 2 LEDs on each leg of the circuit (e.g. a pair of crossing flashers, one on each side if the track), you have 2 options.  You can run them parallel, but if the LEDs are not perfectly matched, one LED may steal all of the current and its partner may not light. You can run them in parallel, each with its own R1/R2, but that messes with your neat circuit board design. The better option is to run the 2 LEDs in series with R1/R2.  This will change the value of R1/R2 to 100 ohms with 5-6v DC supply or 430 ohms with 12v DC supply. For other supply voltages use an online LED calculator for the resistor value.

Bob

OOPS!  I found a small error in the original attachments in my first post. The R3/R4 resistors were shown as 200K; they should be 150K for a 1 Hz flash rate. I attached the modified schematic scan and the BOM in the original post; the only two files affected. The gerbers are not affected. Sorry for the confusion.

FWIW here are the approx. flash rates you should get with various R3/R4 values (with C2/C3 of 22uF):

240K; 0.8 Hz

200K; 0.9 Hz

150K; 1.0 Hz

100K; 1.1 Hz

68K; 1.25 Hz

47K; 1.67 Hz

Bob; thanks for adding the comments on multiple parallel and series LEDs. Good to have that documented here also.

Rod

Rod, did you give any thought on adjusting the component values so this can drive a PW 154 crossing signal that uses incandescent bulbs?  This is NOT the modern 154 that has the alternating circuit built-in.

The S8050 appears to be a fairly beefy transistor that can drive over 1/2 Amp so that should work for incandescent bulbs.  But I'd think you need to adjust all the R's and C's to account for the much higher current flows.  That is, R1/R2 MUCH lower - like 0 Ohms (a jumper wire), R3/R4 MUCH lower and C1/C2 MUCH higher.

Rod,

Thanks for the added values for blink rates, I might try them all and see what happens. Always good to learn more.

Also, thanks for the kind words above, I learned a lot too. Very nice to have a fellow DT'er to learn and consult with. Maybe we will get DT figured out yet! Glad you are getting some interest in the project here too. 

stan2004 posted:

Rod, did you give any thought on adjusting the component values so this can drive a PW 154 crossing signal that uses incandescent bulbs?  This is NOT the modern 154 that has the alternating circuit built-in.

The S8050 appears to be a fairly beefy transistor that can drive over 1/2 Amp so that should work for incandescent bulbs.  But I'd think you need to adjust all the R's and C's to account for the much higher current flows.  That is, R1/R2 MUCH lower - like 0 Ohms (a jumper wire), R3/R4 MUCH lower and C1/C2 MUCH higher.

Stan, actually I did not consider that, but good idea. I am thinking the mosfet 1 amp led version would be able to easily drive these directly without any mods at all, given the fact that the mosfets I used are good for 20 amps. The only limitations would be the traces on the circuit board, but I don't think a couple of small incandescent bulbs such as 53's or 1445's would be a stretch. Not real sure just what bulbs the PW 154 uses,. I may have a couple around here somewhere, but exactly where is the question.

Just waiting for my first batch of mosfet LED boards to arrive so I can do a test build and try things out. If all goes well I will try running a couple of 432 bulbs with it and see how it fairs. After some checks and undoubtedly some tweaks, I can put the gerbers up here for anyone else to try out. Even though the breadboard mosfet circuit works well I don't like rolling out an untested board in case there are problems.

Rod

rtr12 posted:

Rod,

Thanks for the added values for blink rates, I might try them all and see what happens. Always good to learn more.

Also, thanks for the kind words above, I learned a lot too. Very nice to have a fellow DT'er to learn and consult with. Maybe we will get DT figured out yet! Glad you are getting some interest in the project here too. 

Hey thanks for the comments RTR. One thing I can't seem to figure out with DipTrace is how to print the board layout in full page size (schematic printouts are no problem). Mine always come out about the size of a postage stamp in the middle of the page. I am sure there is a way to do it, but darned if I can figure it out.

Rod

Stan, since my mosfet breadboard circuit is still set up I just tried a pair of #432 bulbs running at 12 volts. No problem, works like a charm, and the flash rate is the same at about 1 Hz as it was with the 600 ma LED bulbs. The 432's only draw about 160 ma at this voltage since they are rated for 18 volts. So this circuit would run a PW 154 or two just fine. I have not done costing the mosfet version yet but it would be about $1.50 more than the $4.75 of the low power led version, simply because of the addition of the mosfets and 1N4002 diodes, and the board is slightly bigger. Well worth the cost of admission though IMO!

Rod

From the file menu use 'Preview' just above the Print selection. There is a box up at the top toward the middle that allows you to adjust the 'Print Scale', I adjust that to get the size I want. It only goes to 400%, but that is much better than the default, sometimes even too large to fit the page depending on PCB size.

If you want to change the 'Portrait/Landscape' setting I had to go to File menu, then Titles & Sheet Setup and from the window select 'Print Settings' right side toward below the top of the of the window a bit. That was the only way I could change that setting here. 

This is all from within the PCB design program part.

OK thanks Tom; that seems to work, especially after you find the toggle to allow you to move or center your board on the sheet! Thanks for that help!

Rod

Rod Stewart posted:

Stan, since my mosfet breadboard circuit is still set up I just tried a pair of #432 bulbs running at 12 volts. No problem, works like a charm, and the flash rate is the same at about 1 Hz as it was with the 600 ma LED bulbs...

Nice.  I like your thinking - FET version is the way to go for driving incandescent bulbs.  Can easily handle multiple flashers in parallel.

I'm with Stan, a decent FET will handle amps with little heating, maybe you can automate some real track crossing signals.

You are most welcome. 

Attached is an Excel SS that can be used for finding more exact values for the R1/R2 ballast resistors for the board in this topic. The variables are AC or DC, bridge D1 in or out (for DC only!), supply voltage, target current per LED, Vf, and the number of parallel LEDs; 1,2,3,4,or 6. You should be able to open this with any version of Excel from 2007 on, or Open Office, and others I am sure.

For those who don't care for spreadsheets there is also a PDF version attached with fixed LED current of 15 ma, and Vf of 2.5 volts; pretty common values. You can simply print it out directly.

Hope this helps, 

Rod