Archive for March, 2008

Camera train

March 31, 2008

I like model railways so a model railway does not have to be too exciting to keep my interest, but for the general viewing public at a railway exhibition the level of interest has to be much higher. Keeping trains running all the time (unlike on the real railway) helps, but any novelty that you can add is a bonus.

One thing often seen nowadays that miniature television cameras are available is the camera train, where you get to see the drivers eye view as the train is driven around the layout. Most modern locos do not have much room to install the camera, and no convienient central window, so I have decided to put the camera in a driving trailer.

The pictures show all of the bits (including the tiny TV camera). I started with an ordinary Mk3 brake coach and purchased the Hurst whitemetal conversion kit for it. It is not yet finished, still need some filling and painting, but I will keep you posted.

I took the photos and wanted to post this on Flikr tranny photo day ( http://www.flickr.com/groups/ftd/ ) but by the time I had sorted it there was not much tranny content left! Should I post it?

Suzie x

Pin multiplexing on microcontrollers

March 30, 2008

When using microcontrollers there is a lot of benefit to be gained by using the smaller ones in 8-pin-20-pin packages due to lower cost and availability in easy to use DIP packages rather than surface mount, so there is a constant striving for more efficient use of the I/O pins to minimise the need to go to a larger package.

A popular technique when driving LEDs for instance is to multiplex the outputs into columns and rows which can be very effective for a large array (for example an 8×8 array of 64 LEDs only needs 16 pins) and is well understood and easy to implement, but for a smaller array such as 2×4, the reduction in I/O from 8 pins to 6 pins is not usually worth the effort. With a bit of extra programming (which is free once you have done it) you can operate a 2×4 array of LEDs with only 5 I/O pins, which might get you out of a sticky situation and enable you to use an 8-pin device rather than have to go up to a 14-pin device.

The trick involves wiring half of the LEDs in inverse parallel with the other half and driving each set of LEDs on alternate phases of a single strobe line. This can be extended still further by driving the outputs by switching the microcontroller’s tristate output buffers on and off, allowing the I/O pins to be read when the buffers (and the LEDs) are off so that each of the LEDs can have an associated momentary switch to Vss or Vdd (which makes the LED light when pressed). With 5 I/O pins this gives 8 LEDs and 8 switches.

Rant

March 28, 2008

If your website is not sized correctly for the normal day to day traffic it receives and spends a considerable amount of time unavailable anyway, is it a good idea to hold a 24-hour web only sale where all prices are reduced but only if ordering via the web?

Best ask Rapid Electronics that one.

As much as I like them for having a trade counter just around the corner with a huge stock of components off the shelf, I do get frustrated at having to refer to the (free) paper catalogue when the web is unavailable, and now the cataologue is so big I am having trouble finding somewhere to keep it.

The beginning

March 27, 2008

Hi

Probably a bit late to be starting a blog since the bandwagon has long passed by,  but it will be better than talking to myself (I think!).

Is this the beginning? No. I have been dressing up at every available opportunity for twenty five years and electronics is a way of life. I intend to use this blog to document my thoughts, on trannying and on the more technical side.

So, do I have something to blog about today? Well yes. There has to be a  first time for everything, and even someone of my advanced 
years can have a new experience.  Today was the first opportunity in a while to dress up and 
the first time to try putting on makup properly since I got my TV stick, and so I thought a good 
opportunity for a DIY photoshoot in the garden. Not everything goes to plan of course, having 
a new camera does not suddenly make me an accomplished photographer, so do not expect to 
see any more photos than the ones I have uploaded to my profile – and they had to be cropped.

Suzie x
TechnoTranny