Sorry, Brian.  I've been watching Morse.  I'll have a look under the magnifier.




Please excuse the rough drawing, but I thought it would be the easiest way to show you.

Interesting that there are two versions of this LB101 board. I think Max has the older one, as the other photos I have found look as if they have less components - more integration?

Anyway, it is clear that they DO use voltage dropping diodes in series with the power feed to the tracks. Both J & K are fed into the longer connection block, but only K (K1 and K2) go on to the block rails via a pair of back to back diodes for each. The J connection is direct for the J rails. The reason both J & K are fed into the LB101 is that there is circuitry, which I think includes the Sand coloured chips which detects power loss to ensure that the latest state of occupancy is remembered until power returns - seems to be a common feature with most proprietary occupancy detectors.

The pairs of back to back Schottky are very impressive. They "switch" very rapidly which means that they will pass the DCC digital waveform at high current loads with little deterioration of the signal. Using ordinary power diodes like the 1N series causes the leading edges of the DCC pulses to rise more slowly so could, potentially, cause errors at the decoders.

However, this means that there IS a voltage drop. Albeit less than 1 volt, it is still there, so why there is not a problem during the loco pushing test, I don't know. Clearly the optoisolators - which is what I think the two 8 pin black chips are - are very sensitive as they must be turning on with less than one volt across their emitters - but it is still more or less, the established basic circuit of current detection through the voltage drop across a diode.

I do note this from page 2 of the LB101 manual:-

[user=422]Geoff R[/user] wrote:

Ok here is my contribuition to this trans global experiment

Pushing a loco from an undetected point to an unoccupied detected block turns the block pink immediately the front collecting wheel bridges the insulated gap

Pushing a loco from an undetected point to an occupied detected (pink) block turns the block white immediately the front wheel bridges the insulated gap…….it remains white until the rear collecting wheel clears the gap when it reverts to Pink.

You can check the status of occupancy detectors on the Lenz Throttle. Not surprisingly exactly the same result was mirrored on the throttle.

You guys probably know this already but this doesnt happen if, rather than push, you drive the loco, however slowly, using either the Lenz or TC Throttles. The occupied block remains pink when the front collecting wheels bridge the gap. So I am not clear how I can put this phenomena to practical use.

 Interesting that there are two versions of this LB101 board. I think Max has the older one, as the other photos I have found look as if they have less components - more integration?

I think it is the other way round……I received some yesterday and they are identical to Max's. I have used a lot over the past 3 years and they have been like this for a while. The first few I installed were slightly different. I am guessing the V2 stands for version 2.

Anyway, it is clear that they DO use voltage dropping diodes in series with the power feed to the tracks. Both J & K are fed into the longer connection block, but only K (K1 and K2) go on to the block rails via a pair of back to back diodes for each. The J connection is direct for the J rails. The reason both J & K are fed into the LB101 is that there is circuitry, which I think includes the Sand coloured chips which detects power loss to ensure that the latest state of occupancy is remembered until power returns - seems to be a common feature with most proprietary occupancy detectors.

The J connection from the LB 101 to the rails is optional. For easy access I mount my LB 101s in clusters at the very front of the baseboard and have longish (24") feeds from K1 and K 2 to the rail. I feed the negative J with short droppers direct from the DCC bus for that sector that runs down the centre of the baseboard

However, this means that there IS a voltage drop. Albeit less than 1 volt, it is still there, so why there is not a problem during the loco pushing test, I don't know. Clearly the optoisolators - which is what I think the two 8 pin black chips are - are very sensitive as they must be turning on with less than one volt across their emitters - but it is still more or less, the established basic circuit of current detection through the voltage drop across a diode.

Looks like it does what you expected in Canada at least……………now back to do more wiring and with a clearer understanding of what I am doing:cheers 

[user=434]John Dew[/user] wrote:

Pushing a loco from an undetected point to an occupied detected (pink) block turns the block white immediately the front wheel bridges the insulated gap…….it remains white until the rear collecting wheel clears the gap when it reverts to Pink.

You can check the status of occupancy detectors on the Lenz Throttle. Not surprisingly exactly the same result was mirrored on the throttle.

You guys probably know this already but this doesnt happen if, rather than push, you drive the loco, however slowly, using either the Lenz or TC Throttles. The occupied block remains pink when the front collecting wheels bridge the gap. So I am not clear how I can put this phenomena to practical use.

I need to go lie down in a darkened room to think about that one! I cannot understand why the occupancy detector would act differently with the throttle off or on? There will be more current flowing, but why that makes a difference, I don't know right now?