Note: All design, source and PCB files are located on GitHub. Please see that site for all design details.Railroad Grade Crossing Signal Controller (GCSC) I built sometime back in 2009. The original circuit was quite a mess. In fact I can honestly say I had no idea what I was thinking. Transformers? Power Transistors? A 555 timer? Very difficult to build and get working the first time and consistently, let alone make another.
So like most projects having a chance to rethink it is always very enlightening. This time I built a PCB and used a Microchip PIC12 microcontroller. Probably overkill, but the flexibility a microcontroller offers is unparalleled to discrete hardware with resistors and capacitors. Although the controller only has 25 bytes of RAM and 768-bytes of ROM it is still way over powered; but at the low end of the product line, it is perfect for this application. In addition the new MCU based controller, I also built in a small switching power supply. The lamps and bell are now both driven by MOSFETs. No bulky transformers and no moving parts. The controller does pretty much what the old one did. In response to a button press it turns on the lights (alternating) and strikes the bell about every 2/3 second for about 30 seconds or until cancelled with another button press. A long press keeps the signal on till pressed again.
Another thing about this board is you will notice is that there are plenty of breakout pins available for the microcontroller and output MOSFETs and input trigger. The addition of an ICSP header also allows this board to be directly programmed with a Microchip PicKit3. This along with the on-board power supply makes this board a nice development system for future projects as well. The board will accomodate any 8-pin Microchip PIC MCU.
I also am trying to give GitHub a try. GitHub provides a free collaborative development environment for open source projects. I have posted to the repository a complete set of design files. This includes my design documents, source code and hardware files to build the controller. A link to the project site can be found here. All project files for the controller are available and maintained on that site. All further updates will also be on that site. Please feel free to use and improve on my design.
One of the tools I found very helpful in creating the new design is Google (now Trimble) Sketchup. What a great tool. The tool is free and you can view the board in 3D, allowing you to spin and rotate the board in any direction. You can find my model online here.
I plan on writing a detailed project build on the Make:Projects site on how to build this controller as a kit. I will post an update when that happens. Hopefully for now these photos and the link to downloads below will suffice. As always please feel free to contact me if you require any specific details. I am happy to help where I can.
You can order the blank PCB from the folks at BatchPCB by clicking here. Cost of the board is about $11 plus $5 shipping and $10 handling. A bit steep for just one board. You might try others board houses such as iTeadStudio which tends to be a little cheaper as they will send you 10 boards for around the same price. Delivery times are usually on the order of 2-3 weeks in my experience.
Feel free to contact me with any questions or help you might need.
Thanks for looking!