dbrb2

Thanks @crossland - the interference was when on a short length of track with other trains. Yes, I can see that the recovery time of "normal" diodes might mess with the comms - I will try to remake the circuit with these diodes: https://docs.rs-online.com/a661/0900766b809285fd.pdf Which claim to have an ~50nS recovery time. The 2W10 I was using didn't have a published recovery time - but I suspect it was higher than this. Presumably the charging current should only affect the DCC signal if the cap is almost empty - and a high ciurrent causes the supply voltage to drop, confusing the DCC decoders? Either way, worth doing Weekend job i think!

Ok. It's working... I think it was dodgy wiring. So my next job is to check absolutely everything :-) It does however seem to much up the DCC signal for all my other devices when running!

Tested with a bench supply - still working with input at either polarity, 12v However, the output measured from the rectifier, measured across a cap, is only showing as 4mV when connected to DCC To rule out wheel pickup issues, I have wired the DCC cables directly into the rectifier input, with no change in behaviour

I've run the buck fine from a DC bench supply, so I don't think it is overloaded....but perhaps it could be the diode speeds The DC PSU into the sprog is 12v, 3A so should be sufficient

Hi, See below for a quick sketch. Currently the diode ring is a 2W10: https://www.tme.eu/Document/7e56b3ff02696edf1da0b6fc01e74154/2W005-2W10.pdf I have some of these available though if needed: https://uk.rs-online.com/web/p/schottky-diodes-rectifiers/6289984 The 5v is being used (or not) to charge a backup battery for a piZero - which will draw very little current in normal use. However, when testing on a bench supply, with the batteries dead, the unit sourced almost 15w - so about 1.5A from the track supply at ~12v. This should be within the rating of the 3A supply I am using though.

Thanks. I think the circuit I have then should now be working - it is a boost circuit with a small electrolytic across the bridge rectifier outputs. The bridge is not using high speed diodes currently - I can rebuild it at the weekend if needed. Certainly from a DC supply this works fine - though I haven't been able to test it with a high frequency signal other than with the DCC system. I have the SPROG3 set up and connected via USB to a laptop, with a 12v 3A DC supply. The PanelPro UI shows "track power ON", and throttle 100% - does this mean that there should be a DCC signal on the rails from which I can draw power? If so, then that is a worry, as I am not seeing my expected 5v output. If I have missed a step though then perhaps all is still OK :-)

It did appear to be working with the track power wired directly into my rectifier circuit. Then at some point whilst transfering it to the actual train something stopped working terminally on the buck - perhaps I shorted something... I will try again! DCC track power to general purpose 5v supply is what I hope to end up with - since so much runs gadgetry from 5vdc now. Cheers for all the advice :-)

A function-only decoder is an interesting idea. The project involves powering a pi-zero. To avoid brief drop-outs in power, I have linked this with a piSugar battery. Power pickups are from copper bushes on the axles of the unit. Most of the time this battery will hardly draw anything, as it will be full...but when empty it can draw up to 1.5A @5v as it charges. That would only be about 0.7A at 12v though, so maybe a DCC decoder would do the trick - with the output fed into a buck converter to give me my 5v charging supply. As you say, the ability to turn on/off remotely is tempting. It looks though like many would not provide this current on a single output, so I might need to combine multiple output channels...?

Thanks - my use case puts this inside a carriage, so I suspect your very neat package may not fit? I will see if adding a capacitor this evening helps. It feels like it might....a perfect square wave shouldn't need one.....but maybe in the real world I do! If that doesn't work, I'll have to think again!

Thanks. I will try a cap this evening, and faster diodes later this week if needed :-)

Ok thanks. I'll have a look this evening. At present I am using one of these bridge recttifiers: https://www.tme.eu/Document/7e56b3ff02696edf1da0b6fc01e74154/2W005-2W10.pdf Feeding into a buck converter to give me a 5v supply. I have no smoothing capacitor at the rectofoer output currently - since the DCC signal is differential square waves, it seemed that one would not be needed - since the voltage at the rectifier input should always be +-12ish volts...however it is a matter of moments to try one and see the effect. Changing the rectifier diodes is not quite so easy...but is doable

Ah Ok - so the tracks have a differential signal on them, which provides enough power to locomotives to run, whilst also carrying data? Looking at this page: https://dccwiki.com/DCC_Power It looks like the signal is differential - so the voltage across the rails should always be ~12v, but the frequency will change at high frequency? Perhaps that is why a multimeter has trouble making sense of it....? My setup today is: Rails > bridge Rectifier > buck converter > 5vDC, which works when the rails are powered from a DC PSU, but not when wired up for DCC If the above is correct - voltage across the rails always 12v but with polarity changing at high frequency, then the output from the bridge rectifier would have no "dips" to be filled by a capacitor would it....but I will certainly give it a go.

Morning I apologise if this is a very basic query: I have a DCC controller - SPROG3, connected to a laptop and a 12vdc PSU It can detect and control a DCC enabled locomotive on a short length of track I have been testing with I also have a basic carriage, designed to take 12v from the tracks, rectify it to deal with whichever polarity is present, regulate it, then power some onboard electronics (lights, camera etc) However, when I check the voltage across the two rails with a multimeter, I measure only ~4mv DC My hope was that the DCC signal was overlaid on the DC supply - so that I would still be able to access 12v for "dumb" power - is this not in fact the case...or is there some command that I am missing to tell SPROG3 to provide 12vdc to the running rails Cheers!