Wednesday, April 27, 2011 the corners of my mind...

Don't recall how I stumbled upon this, but happened to see these in TransGrid's Network Management Plan on the web:
TransGrid owns 137 backup alarm systems that provide a combined alarm service as a secondary service to SCADA SMART alarm [ed: something missing here, TransGrid??]. It is a microprocessor-based system capable of transmitting and receiving 10 simultaneous alarms. SMART alarms currently account for the entire population of backup alarm systems in the network. This system has an expected life of 20 years.
SMART Alarm transceivers have been installed as the backup alarm system. They provide a 10-function alarm service in both transmit and receive directions and have been designed to interface with all of TransGrid’s communications channels. SMART alarms currently account for the entire population of backup alarm systems in the network.
This system has an expected life of 20 years and at present there are no performance issues.

source: TransGrid Network Management Plan 2011_web.pdf  pages 55 and 68

The "SMART Alarm" was a project I completed back in 1997 while working at TransGrid. I don't recall how it came to be called the SMART Alarm...I think it may have been because it was microprocessor controlled, which was a huge leap forward from the op-amp filtered, 5-pulse-rate alarm system designed in 1982 that it was replacing.

The "designed to interface with all of TransGrid’s communications channels" means that originally, it was designed to work with 50 baud E&M signalling channels, over either a power-line carrier or microwave radio link. Yes. Fifty baud. You can almost watch the bits go by.

I still have a copy of the manual I wrote for it, which covered the basic theory of operation, installation and configuration.

From the Hardware Overview section of said manual:
The SMART alarm system is a 10 input, 10 output microprocessor controlled status transmitter and receiver built on a singe 220 millimetre length Eurocard board, designed to operate from a positive earth, 50 volt DC supply. As the system is fully microprocessor controlled, the flexibility of the system is limited only by the hardware constraints of the board, and what can be programmed in software.

I have fond memories of that project; developing the design, the PCB layout with Protel on Windows for Workgroups 3.11, writing the software for the 8051 in assembly language. Good times. PCB auto-routers have improved a lot since then, though. If I recall correctly, it was painfully slow.

So, a device installed in over 130 sites, with an expected lifespan of 20 years. And (to quote from the report) "no performance issues" as of 2011?

I must have done something right!

Thursday, April 14, 2011

Smaller and smaller and smaller

I didn't really appreciate how small these bluetooth modules are, until I got one delivered today.
The one I've got isn't exactly like the MDFLY one (linked above), but it's the same CSR BC417 chipset, mostly the same PCB layout - I'm pretty confident they're equivalent.
Which is lucky, because the ebay seller I bought this from sent no datasheet, and has none linked from their ebay page either. Good thing it was cheap. (about $8 AUD, delivered)

Saturday, April 2, 2011

Together at last

The CNC machine is together and working!
It's actually been together for a few weeks now, but I didn't get around to posting about it (because, what's the point of a post without video, right? )
Also, I wasn't happy with the aluminium slides I was using for the central plate, so I acquired some more 608 bearings, and replaced the slides with these.
Each of the slides are now a pair of bearings on a single bolt, separated by a thin brass washer. The lip of the extrusion on the CNC frame sits in the small V created by the gap and the chamfer on the bearing face. So there are now 16 bearings in 8 pairs bolted to the central plate.
I should have taken a photo. Oh well.

Here's the machine in action this morning...

And a photo of the finished product - just a scrap of chipboard, with "Amalie" now engraved in it. Blue chalk added so that you can see the routed letters.
Outstanding issues:
  1. The x-axis threaded rod must be bent, and it's causing a slight wobble when the x-axis moves. I think I'm just going to have to replace it.
  2. The central plate could be stiffer. You can still twist the x-axis a little. I may be able to increase the pressure of the rollers against the runners, but I think the plate flexing is the problem.