magnet (2)


SCMES Track Signals – Track Sensors

My intention is to use reed switches for the track sensors, as they fit the needs of ‘non contact’ and ‘cheap’ (ish).

This method only requires a magnet to be fitted to the riding trucks, leaving them electronics (and complication) free. Furthermore, should a guest driver wish to use the track, they can either use one of the club riding trucks, or simply attach a magnet to their own in the appropriate place.

The innards of a riding truck

The riding trucks have this central bracing, providing a nice mount point for our magnets on the underside!

On the subject of the club riding trucks, and the ‘appropriate place’ – mounting the magnets on the trucks should be fairly simple, as they are constructed mainly from mild steel (and thus, magnetic!) so magnets can be stuck anywhere flat on the underside of the truck giving great freedom with regards to fine tuning.

The track sensors themselves will be simple reed switches arranged in parallel such that any switch action will cause an input on the microcontroller to be pulled low.

These ‘sensor bars’ are to be mounted on the inside of the outermost rail (The left-most rail in the image here) as this is where the origonal sensors (microswitches) were mounted by means of bolts through said rail, thus we can re-use the mountings as they were left.

I’m going to write another post covering the design of the `sensor bar’s once I have drawn up the schematics.




SCMES Track Signals

I’m currently designing and building an electronic signalling system for the South Cheshire Model Engineering Society.

A view across the track site

The Track Site

This consists of a set of 10, 3 aspect (red, amber and green) signals to control and 10 track sensors (the nature of which is to be determined) as well as 3 other special-case sensors (two on traverser locking mechanisms, and one station master switch).

The original system was based around a control unit which worked on digital relays and used 36V lamps.
Unfortunately the designer was involved in a car accident and died, leaving the system unfinished, and futhermore, the method of detecting a locomotive passing a signal (microswitches on plates in the track) resulted a far-too-short pulse length to actually trigger the relays.

This left the system in an unfinished state for several years, during which I finished my degree, and now I have time to work on the project.

A development signal's internals

The three high-brightness LEDs inside the head of a signal

The first order of business would be to determine what the control unit is required to drive, in this case high brightness LEDs are used for each aspect, and, although my development unit had a dead red LED, the LEDs could easily be powered by a simple 6v source (in my case, AAA batteries, as can be seen in the larger image).

The LEDs are more than bright enough to be seen far away, so will be acceptable as lamp replacements.

A signal showing all lights on, except red is broken

They're bright (shot taken from an angle to see anything at all!) except for red, in this case!