Edinburgh Waverley Hot Box Detectors - 1979

When I started in 1979 a project to provide Hot Axle Box Detector (HABD) indications on Edinburgh Waverley Control Panels was nearing completion. Traditionally the HABD Locators (indication and Alarm units) were stacked at the one end of the control panels but for Edinburgh these indications were being placed geographically on the panel.

This was achieved by using the Train Describer (TD) to display the information of wheel count and alarms for Hot left, right and both on two four character TD displays. To provide the TD with the data a new propriety transmission and receiver system was designed. The kit comprised of a small FSK transmitter and a receiver card, the receiver card which decoded the data plugged directly into a TD cubicle slot where the TD computer, an HP2100 took care of reading the data and displaying it on the control panel. Alarm acknowledge and selection switches were hardwired directly back to the cubicle and card.

Being the junior in the team my job was to draw the circuit diagram and by the time I had completed it I was expected to know how it worked! A good lesson there! Unfortunately only some of the design has survived ,the full transmitter design and the artworks for the PCB. From memory the receiver card had eight LED's on the front for axle count (in binary) and three for the alarms Hot Left, Right and Both. Other than that I can't provide much more detail. In addition there was a portable Test Set provided in a fairly large 2U 19" rack case and proved very useful when testing the TD interface.

The receiver PCB was manufactured externally with artworks produced for a double sided board but costs did not permit plated through lots of through pins were required to be soldered on both sided then all the components. Guess who got the job of assembling the boards!

The Transmitter board was photo etched in house as costs did not permit sending out to a PCB manufacturer however they proved very reliable with only one being returned for replair in 2008 after nearly 30 years of service. I understand that a few years later the HABD systems were replaced with modern equivalents.

Motherwell Hot Box Detectors - 1981

Christmas 1981 is when we installed the new HABD interface for Auchengray, a temporary 19" rack with a Coutant PSU attached to the side was placed in the back of the HABD panel. Newly designed four character RED LED displays were mounted on the panel next to its location along with a selection switch and Alarm Ack button & sounder. It was our intention to return in the new year with a nice new 19" rack which would replace all the existing Locators but for some reason it didn't happen. The rack and cards were built and ready to go! The temporary installation remained until the box closed in 2019.

The temporary installation, the aluminium rack is in the lower left of the picture, clearly just thrown in there.

Unfortunately the card design is lost but I remember it was designed on a scroll on the must have been a couple of meters long! The Transmitter design from the Edinburgh project the year before was re-used.
A battery operated hand held Test Set was built using this card, an additional hand wired interface card and an LCD display - HABD card was designed with the portable locator in mind as it could be guillotined to single Eurocard size - it can be seen on the card there is a gap of comonents along the 3U height mark.

During 2021 I spend some time refurbishing some TD display modules to make this short video: