Hello all,
After working on the idea of driving LEDs from track power and reducing or eliminating flicker, I posted an idea using small diodes and a capacitor. I had another think and in my obsessive way to follow up an idea ,I wanted to make the device as small as possible so it could be used in the tightest space.
Hence the following. Use a small surface mount bridge rectifier, add the capacitor and heat shrink. To make it easier to work on I decided to use some paired flexible copper strip I have had for a while. It solders easily and is quite strong. It is not possible to cut the copper strip without damaging it so I used the following idea. Some photos :

This was one piece which I cut with scissors.

A small edge was turned back on itself and squashed flat. This piece is then lightly glued to the end of the other piece. The turned up edge prevents any possible short circuit.

This shows where the bridge will sit when soldered across the join.

Soldered and wires attached, compared to an earlier version.

Final product. 20mm x 6mm at widest point.

Previous versions with diodes. Smallest about 32mm.

The capacitor is strictly not necessary as the LED will not flicker without it but a flashing LED requires it . My friend with a Marklin show layout uses flashing LEDs embedded in track to attract attention to particular areas.
NOTE the capacitor in this instance is connected directly across the output of the bridge and on my ECOS digital layout the DC voltage reads 21.6 unloaded which is RMS (root mean squared) voltage. The peak voltage from rectified AC or digital power will be 1.4142 times that and that is what the capacitor will be exposed to. Hence a voltage rating of at least 35 Volts is required. As a small value (1 µF in this case) is ample for a couple of LEDs in series, the capacitor will still be very small.
Thanks,
Howard.

Hello Tom,
I agree. I understand the digital voltage is a high frequency square wave but on my CRO it seemed offset, i.e. asymmetrical. I wasn't sure if the usual formula applied to this , so I opted for the safe bet of 1.4142 for the post, especially after our recent discussion. I am interested in the track voltage, frequency and waveform and I would appreciate if you could help me out there. ( My background is medical but my interest in electronics arrested at the IC stage !)
Regards,
Howard.

Thanks Tom,
I knew there was a reason I stayed away from computer programming!.
I had a look at the sites and I will now go and take something for my headache.
Best thing from all this for me is that it got my understanding of digital track voltage to a more acceptable level.
Regards,
Howard.

Aha Dale, I see you live on the dark side!

The problem with electrolytics and tag tantalum caps is they are prone to rupture and sometimes do so without warning even with age.
Some cans have a pre-weakened area on the top designed to give way in less spectacular fashion.

Having said that I have a lovely Nixie tube clock in which one of these caps blew up when a 4mm ant got in and shorted an SMD diode. It was totalled , just a brown mark and some scraps of metal left. The designer and maker was kind enough to send me 3 replacement parts I needed for postage only, and I nerved up and soldered them in with success.

I would love to have more electronic theory.

Regards,
Howard.