CTC Machine Build


Rick -

I see that Mouser stocks a C&K 3 position switch that might be useful. I haven’t checked the distance from the panel to the bottom of the switch to see if it is the same as the 2 position Taiwan Alpha, but it is probably close.


Bob, Thanks for putting this info on the forum, the panel looks fantastic. I hope to build one soon.
With regards to the 3 position switch, have a look at mouser part number 105-SR2611F-25-18NS. There is a tabbed washer that controls how many switch positions you can have. I will be setting mine to 3 position. The angle of the throw is correct.


Chris -

That switch would be perfect for the 3-position. Unfortunately, Mouser shows it to be non-stocked with a minimum order quantity of 1000. :disappointed:

Ten years ago something prompted me to stock up on both the 30deg-3 and 60deg-2, long before the A&O track plan was finalized. Fortunately my guess was pretty good, as there are now only a couple spares left over.


Chris -

I don’t know if it is too late, but Mouser now shows stock of both Taiwan Alpha rotary switches suitable for US&S CTC machines. I haven’t ordered any, but from a catalog search it appears that they have both:

60 degree 2 position: SR2616F-0202-18F5B-D8-N

30 degree 3 position: SR2612F-0304-21R0B-D8-N

The latter is actually 4 position, but it comes with a washer with a pin on it that serves as a rotation limiter, so it should convert to 3 positions without any difficulty.

At the moment less than 25 quantity price is $4.24 each.


Bob, thanks of keeping an eye out for switches. Fortunately, like you, I stocked up on switches a few years ago in anticipation/ preparation of building a CTC machine. I’m not sure how many I bought but it was a lot.


Yesterday I finally set up the PC etch tank, which afterwords went in the trash due to extreme cracking. Anyway a prototype replacement for the SMINI PIC processor has been assembled. The firmware is about half complete.

As a refresher, the goal is to enrich the SMINI communications protocol to add a CRC for error detection, inquire error statistics, and read-back output data that was written. Since the processor has EEPROM, it can be made to remember the last-known output state and return switches to their former position (i.e., pre-lunch time.) The normal SMINI powers up with random output states. That might be bad if a lunch call was issued and a train was left straddling an OS switch. (How do I know? That happened when I was a pre-opening volunteer at the Greeley Model Train Museum.)

There is also a micro SD slot for data logging. I’m thinking of swapping out the current Teensy 3.1 processor that runs the CTC machine for one of these, so that log files of train movements and dispatcher movements can be logged. That would assist in debugging and adding new features.

Edit: For electrical geeks, all the parts that Bruce selected for this board have a minimum high level input voltage (Vih) of 2V. The Teensy will output at least 3V given its 3.3V on-board power supply. All the Teensy digital inputs are 5V tolerant. So it should play well with 5V children. External level-shifting circuitry is not needed.


Watching all this thread, and some others, make me think I should go to narrow gauge where none of this is needed… If you only have one trains you don;t need signals. Or orders.