Pretty interesting!

I'm so new to all of this that my question is a very basic one ... but not easy to put into simple words ...  

Your circuit board looks very convenient, neat even.  I do wonder though if the exact components listed are not available, what happens if the "footprint" is different; i.e., I am having a very difficult time locating the small rectifier bridges ... the ones available to me are physically larger that what is used by you and Dr. Geoff (higher voltage rating and 2 Amps).  I am hoping that they will work as I have not found a "cheap" source (i.e., free shipping) online for them ... and shipping from the US would pretty much double the cost of the entire project (as they all want to ship US Priority which seems to run $38 for the smallest package size).

Any how, thanks for posting and lots of good information on your web page.  Anxiously awaiting two more deliveries (the perf boards arrived a couple days ago).  

Interesting

I would be interested in one of these boards.  I have handful of arduino minis on order.  I'm surprised you didn't create just a board with the DCC circuitry and the arduino only, more compact, and just use the pns off the arduino for the servos/led/relay/etc.  Maybe a antidrone air defence system is needed here in Canada ( a little humour ).

Where can I find more info on these DCC libraries and their functionalities.  Is it Railstars or is there any conection to it???

What kind of waveform does pin 21 receive. 

Is it +5V when DCC square wave is high and 0V when DCC Voltage < = 0V + diode Voltage.

Make your own Bridge Rectifier

Dave - Just about any bridge rectifier should work.  You can even make your own from 4 diodes  - I added a section on the web page that shows how.

http://www.trainelectronics.com/DCC_Arduino/Decoder_board/#make_your_own

dave

Arduino DCC info

The work that Geoff and I have been doing is based on both the Railstars web page:

http://railstars.com/software/cmdrarduino/

and information found here:

http://mrrwa.org/

Pin 21 as it connects to 5 volts DC, shouldn't be any waveform there at all!  The DCC signal is applied to pin 5.

Your confusion may be due to my leaving a connection off of the original schematic - it has been corrected.

FYI, DCC looks like this at pin 5 on the Arduino.

dave

Power problem with 3 servos resolved

You may have noted that I used a source of external power (a cell phone battery) to power the servos in the video.  I did that as the system was shutting down when I tried to operate two or three servos.  It turns out that the problem was not with the circuit or the servos but with the DCC system that I was using for testing.  It is composed of a laptop running JMRI and a SPROG II controller. 

The SPROG II was the problem.  It must have a very sensitive shutdown circuit that detected too much power being drawn.  When I tried 3 servos using the board's power supply with another DCC system and with the SPROG II and a 3 amp DCC booster it worked perfectly.

dave

PS I just found this note in the user manual:
 SPROG II will remove track power if output current exceeds 250mA as measured 100ms after applying power.

PCB Design

Great work Dave.

Would you be willing to share the PCB layout file as I would really love to try the design out?

Steve

PCB files for Decoder Project

Sure thing, Steve-  here is a link to the files:

http://www.trainelectronics.com/DCC_Arduino/Decoder_board/#The_Gerber_files_for_this_board_are_here:

The ZIP file includes the Gerber files and the source file (ends in ".fpc") for FreePCB, the program I used to design it.

A few things I would change include making the holes for resistors smaller and the holes for the transistor a bit larger.

Enjoy.

dave

Bridge Rectifiers ...

Thanks for that bit of information, dave.  I am able to get bridge rectifiers, just not the ones specified.  I figured anything with a higher rating would work, so have several to try out ... main issue is the "footprint/packaging" are a bit different.

For the cost of the parts I figure that the learning experience alone is well worth it.  Thanks so much to all of you who have contributed your ideas, codes, and schematics.