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It would only have a small area to grab with, and a lot of resistance to work against, so I'd be surprised if it would do it. But I didn't think of trying any, I must admit!

lol, yes quite possibly! 🤣

Hi Simon, thank you for your kind words and for taking the time to write-up those suggestions, and for offering future help - I may well need it! I've made a note of the PIC18F27Q43 as a potential thing to look into, thanks 🙂

I don't own any Z myself, but this is half the size.

Thanks for taking the time to write up that extra information, and for reading through the other comments to see what people have said. Interesting about the optocouplers - quite a few people are keen on those. I'll give a few things a go and see what kind of results I get - if the code is successfully getting the instructions I think the controller should be sending, and with enough time to do something with it, then it'll achieve what I'm after 🙂

Thanks for the info. If it did that wouldn't it end up reading the 13V square wave as being around 9V? 13 / (2^0.5)

@@endoorrailway @endoorrailway Vrms = 13V * 0.707 = ~9V, but that would be for a AC sinusoidal wave, not a bipolar square wave .. The cheap DMM can't make sense of it since it also lacks a true zero crossing. The bipolar square wave isn't referenced to a fixed ground, it's floating. So it's not a true AC signal, where the reference (N) is at a fixed potential. Your measurement in DC mode is just the average it sees over some time, it's simply too slow to measure the signal.

OK thanks .

Funny you should say that - in the summer I visited Cadbury World at Bournville - in their museum section they have a model of the factory and surrounding town, which at the edge has a railway line. The track looked very much like T gauge track 🙂

Several other people have mentioned PIO too, thanks 🙂

Yes there's something fascinating about miniatures 🙂 It's definitely a good size for squeezing a bit of railway into a small space.

Thanks 🙂 I found writing the code to use interrupts pretty easy to do, though the polling code is also easy. I think I'll start with an interrupt-driven approach when I move to C. I have no idea what I'll actually be able to achieve with the circuit, but I'll have the freedom to make it a non-standard shape to fit the spaces in my locos, so that might help. I feel a long way off that yet though!

Thanks. The polling wasn't my first approach, but it was the one that worked best in MicroPython. I'll be moving away from MicroPython for this - I was hoping it would do the job, but it doesn't seem to.

@@endoorrailway At least with python you gave it a try and got to know a bit better about whats happening. Thanks for sharing the video

Thanks

Thanks 🙂

Thanks 🙂 With the various different suggestions I've been given I may well have to give in and buy an oscilloscope, just to see how the different approaches compare. Thanks for the component code - when I get a chance I'll need to go back through these comments and make a list of the things people have suggested and do some online shopping!

Ah, yes, not much space for fishing them out! I intend to have a tunnel at the South-West end of the layout (Kennaway tunnel) - I'll have to make sure the side is removable.

It's a trick of the camera - they're actually very happy as they are 🙂

Haha, yes - I hadn't thought of that, but I've got the USA edition of Ticket to Ride which has the smaller vehicles (compared with other editions I've seen), and they're a very similar size!

Thanks 🙂 And thanks for the suggestion. The various helpful comments on this video have served to remind me just how little I know about electronics! Diodes just control which direction current can flow in, if my understanding of them is correct, and so I used them to split the signal - but the signal is at 13V, which is far too high for the Pico's (or other microcontrollers') inputs. Is your suggestion that, essentially, only a large enough resistor is needed in order to reliably reduce the voltage from 13V to 3.3V after the diodes? The Pico has internal pull-up and pull-down resistors, which one to use is configured in code, so at this stage I don't need to add any for that purpose as far as I'm aware.

@@endoorrailway With a diodes mounted the way I suggested, the current should only flow to through the diode and pull the input down to 0V when there's 0V on the rail (suggest using similar diodes as the rectifier to have the same voltage drop). When the rail is at 13V the diode blocks and pin is pulled up to 3.3V either internally or with a resistor. Probably not necessary to monitor both rails, then you can use only one diode and input. But I think a setup with an optocoupler as some already suggested is the most optimal way of harversting the signal.

Ah I see, that's neat, thanks!

I've never looked at a Nano Pi before, but it looks much more like a computer than a microntroller - what I used here was the Pi Pico. I don't think there's any option of having standard Python on that - MicroPython is all I've seen - but I've got no idea how it implements Python on the Pico. Without an operating system being present it must be quite different, but to work like Python it must still have various inefficiencies. I know that standard Python gets compiled to bytecode at some point (the .pyc files that appear), but is still an interpreted language. The RP2040 sounds like it's one of the computers on a chip - I'll have to assess more options when I get to the stage of making something small enough to go into a locomotive. I've got no fear of programming in C or C++ - I've done that before - but I've got a lot to learn about doing it with microcontrollers and in some cases even just how to get the code flashed onto a chip seems complicated! All good fun learning it though 🙂 Thanks for you ideas and taking the time to write that up 🙂

In what I was reading I didn't come across anything that suggested implementation solutions, it was just specifying what needs to be achieved, but I haven't read through most of the documents - I was just trying to get started somewhere. The various specifications are at www.nmra.org/index-nmra-standards-and-recommended-practices A few other people have suggested optocouplers too - I'll have to take a look at what's available - ultimately I'd like to make something that fits into an N gauge locomotive, so small surface-mount components will be needed. I'm sure there's be optocouplers that fit that constraint though 🙂 There was a nice guide about interrupt programming I read that's part of the MicroPython documentation; I'm not sure what other interrupts would be going on, but it seemed to be saying that all of the same priority would queue up if they overlapped, so I just left them at default. Maybe there are others happening that I don't know about, but I think they'll also be affected by the voltage regulator potentially distorting the timing, so there seem to be a few ways in which I could improve things. Thank you for taking the time to share that useful information 🙂

@@endoorrailway i tried reading the spec, thanks for the link, but it seems they do not concern themselves with the actual interface, and these are proprietary. must first admit my electronics technical degree was a very long time ago, and i am very out of practise, but i think you could use a PC817, with an appropriate current limiting resistor, directly across the track signal, and you could then connect the ouput directly (and safely) to your GPIO pin. if the track voltage changes, though, you would need a different resistor.

It didn't take you long to scan a lot of information there! With a degree like that you'll have forgotten a lot more than I'm likely to learn in this field. Thanks for the suggested component - I'll have to start making a list of the various things that have been suggested.

Also when thinking about capturing bits, think in terms of time rather than voltage. Quick toggles vs slow toggles.... this should be easy for a PIO block.

Thank you very much 🙂 It's getting a lot more views and comments than is typical for my channel, so I think it's ended up appealing more to the general electronics hobby or pros than to just model train-loving folk! Thanks for mentioning PIO - I haven't spent much time to date working with microcontrollers and hadn't come across it before making this video, but others have since mentioned it too. I'm glad you like Picos too, but ultimately for this project I'm aiming to use something physically smaller than the RP2040 (some kind of ATTiny is what I have in mind), so I don't intend to go down the PIO route because it looks like it's specific to the Picos, but if I were sticking with a Pico then it does look like a good way to go. I'm glad you enjoyed it, thanks for letting me know 🙂

@@endoorrailway there are quite a few _really_ small RP2040 and RP2350 boards, magic word is 'stamp'....

A stamp is too big for a lot of N gauge locomotives. For what they have crammed inside these systems on a chip are a real marvel of engineering, and so cheap for all the wonders they perform, but at 6.5-7mm square the RP2040 takes up a decent amount of space that I'll need for other bits and pieces like optocouplers, resistors, some kind of non-volatile storage, motor driver, amplifier etc. - I know there are less capable but much smaller chips around. I really don't know what will work, ultimately - I may well end up with an RP2040.

This is the first time I've tried to work with a digital signal at this level, so it's all "DCC stuff" to me, but it seems likely the engineers who designed it were familiar with other similar things like canbus and took inspiration. That would also help other engineers understand it and work with it easily as there'd be familiarity.

@@endoorrailway yes true, in fact just about all signalling systems have evolved from another before, no matter how complex they make it once it passes through circuitry it all boils down to just 1's and 0's. this one is fairly basic in that theres no error correction just bad packet skipping, you want an headache, look into a cd players data stream thats designed to cope with random flipped bits from noise/dirt of the disc, its amazing how they even came up with it and I'm glad i'll never have to try to code for it....

At this stage I'm pleased that the error detection is just skipping and not correction! Yes I've been impressed with how well CDs can play even with a decent amount of scratching on them. I think that's going to be at a complexity beyond what I dabble in during my hobby time 😉

Thanks 🙂

I knew there must be a formula, thanks! With 26μs samples a DCC "one" of 64 could potentially be measured as lasting 78μs, but the shortest a DCC "zero" could be measured at is 104μs. But with a 29μs sampling frequency a similar thing comes out - max One is 87μs, minimum Zero is 116μs. I must admit I keep having thoughts like this, but eventually find a scenario that proves me wrong. So far 29 is the largest I've come up with where (I think) there can't be an overlap in interpreting the longest One and shortest Zero. Thanks for mentioning PIO - it's not something I'd come across before making this video (I've not got a lot of experience with microntrollers), but a few other people have mentioned it since. I think it's specific to the Pico, so I'm not intending to go down that route to start with because there are physically smaller microcontrollers around, so I'm expecting to translate what I learn to another architecture. Thank you for taking the time to explain those things 🙂

Most of my programming experience has been in Java, but I've done C, C++ and some C#. For the most part Python has come out as my favourite in the last few years, though it heavily depends on what it's being used for 🙂 I've been wanting to avoid going down RP2040-specific avenues, like PIO, but so many people are suggesting it I might have to do it just to see how it goes and report back in a future video. Thanks for taking the time to share your thoughts 🙂

@@endoorrailway I imagine IDEs and debuggers make it easier to deal with these days, though I still dislike white space as a syntactic element - you could severely mess with someone by adding a space before one of their tabs in an if block (though I would hope that the compilers would flag that, they didn't 15 years ago). The unit I was programming was a black box hit and hope - you downloaded the program to it and hit reset, then it either did what you expected or not. I did find a compiler for PC that would at least allow me to test out the processing and data structures in a controlled environment but anything to do with the cellular modem was a wing and a prayer since there wasn't a serial port to pass any response codes from the modem back to a PC for debug. I still shudder with that one, it was a pain to get working reliably wherever in the world it was deployed and it should have been a simple case of slap a local data SIM in and off you go. With regard to the PIO I think you will find it worth looking at as it is pretty simple, especially if you are familiar with assembly. The state machine code is severely limited in size but it would still take quite a load off the main program and you could do the pulse measurement down at what is effectively hardware resolution and pass the bits over to an interrupt handler in Python to handle the protocol. I said I would leave the hardware alone but I have to add one thing: I would sample the second rail to be able to filter out any glitches to ensure reliability, I imagine a railway layout is electrically noisy. My own choice would be to use a pair of optos to interface it to the Pico's power; a couple of resistors and some cheap optos would firmly isolate it from the track power and allow a check to ensure that the two signals were truly complementary. Obviously YMMV.

@@TheOwlman Thanks for you further thoughts and taking the time to write them up for me 🙂 Perhaps I'll find that ultimately I want to measure both rails, but with the commands being repeated I suspect it's not going to be necessary, so keeping the componentry and code that little bit simpler is very appealing. I'm also right at the start of this project so although lots of people such as yourself have kindly provided lots of useful and sensible information, it's too much at this stage for me to be trying to incorporate all of it. Thanks 🙂

That would be nice - it would allow you to make big buildings.

I think it would be great if it got popular, but regardless of how detailed or well it runs, unless it somehow becomes dirt cheap I think it's just too small for most people to be interested in buying.

There's no way I'm going to try taking this apart unless I really need to, but I suspect the motor is this one: www.tgauge.com/product/500/motor-with-gearbox

Thanks for you ideas. I haven't, not beyond a quick test immediately after fitting a DCC decoder. I know that on several of them the wheels rub against the underside of the chassis. I guess I could try rolling the bogeys along by themselves - that would show how well or not the wheels roll.

Thank you for your thoughts. I'll definitely be moving away from the voltage regulator between the signal and microcontroller inputs! Execution time will always be relevant - even in an efficient language and triggered by interrupts, instructions must still be executed for anything useful to be done. But knowing that C is a lot more efficient, and from what others have commented, I'm expecting switching to that make a big difference. Thanks 🙂

@@endoorrailway Also, get yourself a Pico 2.

@bexhillbob I probably will at some point, partly because I'm interested in trying Rust, but I don't think I need the RP2350 for this project.

My dad used to engage but then he's got h for a Christmas tree train

Thanks for the encouragement and for taking the time to write up that information for me! I've been a bit baffled by ground coupling for a while - often things I buy seem to require it, and the common ground on the electrics of this layout seem to link lots of things. I would much prefer things to have more isolation, so if optocouplers are small enough then I'm in favour of trying them 🙂 I did actually start off with interrupt-driven code, but I couldn't get good results and switched to the polling, which worked better. However, the interrupts will be directly linked to what the voltage regulator is doing, so that could well be a source of issues from what you and others have explained to me. I did actually read through a detailed interrupts tutorial from the MicroPython documentation before writing any code - it gives lots of useful information. I don't think there are other projects I'm going to want an oscilloscope for, so I'll see how far I can get without one - I'm pretty sure the signal at the tracks is going to be good because I've got plenty of trains receiving instructions correctly, but I admit it would help with diagnosing the issues I've had! Based on all the helpful comments like this one, I think a combination of switching to C and for now using a voltage divider (both things I should be able to do soon without doing shopping), are likely to bring much better results 🙂

@@endoorrailway optocouplers can be extremely small. Definitely give it a go. One side behaves exactly like an LED, though you never see the light; the other side is often a PNP or NPN transistor with exposed collector & emitter. There are many, many example circuits on the net.

Great, thanks 🙂

I played around with all this a couple of years ago (for Scalextric Digital, which also uses DCC)... I can wholeheartedly recommend all these suggestions. I know a scope is an investment, but you're doing everything blind without one. I went for a Hantek standalone unit for under £200, but USB ones which use your PC to do a lot of the work are £50 or less.

I had a bit of a look at oscilloscopes today - it looks like they'd need to have megahertz bandwidth, and then it was unclear to me if ones that said they're 1 or 10 MHz can handle square waves at that speed. I'll see how far I can get without one - I can be confident that the signal at the track is OK because 30+ locomotives all respond to commands just fine, and I know from the NMRA specs what the signal for the commands should be, so I'll only need to get an oscilloscope if I get stuck. Thanks for the comment 🙂

Thanks for your thoughts 🙂 I think a regulator from rectified power for the microcontroller would be sensible, and actually the DCC specifications say decoders should be able to work with up to 20V from the track, so I imagine it would help with that. I actually started out using interrupts but got worse results that the polling; however, from what others have said it seems that could be at least partly to do with using the voltage regulator for the signal.

Thanks for the theory; in AC mode it does measure the DCC track voltage (without any of my diodes in place) as the expected 13V, so it must be taking a proper average to get that. The readings where it was 2/3 of full voltage were when it was in DC mode - I don't think it should be doing any kind of RMS (or an approximation) for DC, if nothing else because it would never produce a negative value. In DC mode it does correctly measure normal DC signals, like the supply for my LEDs, or the terminals of a 9V battery, as being at the expected voltages. Maybe I need to put it into AC mode and see what it makes of a single track's signal through the diodes - I didn't do that because the current isn't alternating. This multimeter was about £7, so it's not going to be a fancy one.

​@@endoorrailway If you were to give your multimeter on AC a 13V sine wave, the peak voltage is going to be 1.4 times the RMS value, and the meter is calibrated to tell you that the RMS is 13V. This is the cause of your 2/3 and 3/2 values, though they sound like the average, rather than the RMS. Try that AC read on a 9V battery and see what you get, compare the DC and AC readings, that should calibrate the reading in your mind. Most multimeters measure AC by rectifying the AC to DC and then dividing by 1.414, the square root of 2 (or multiply by 0.707, the inverse, it's the same result). This matches the definition for measuring an AC value, that it should come out the same as the DC voltage that would deliver the same POWER. (if you have root 2 times the voltage, you get root 2 times the current, and volts x amps = power.) For most multimeters, your AC range will read 13V RMS AC as being 13V and it will usually do the same for 13V DC, though it may say 18.3V... A smart multimeter will recognise DC and scale itself accordingly, though most simple multimeters are not that smart. You could try this and it will be informative. It would seem that when no instructions are being delivered to the track, it rests at 13V DC. You could tell by putting a DC-only engine on, it should go like Mallard... Multimeters are a black art that I mastered in 1973, but now can't explain very competently. It's been a while...

@neilbarnett3046 thanks for the information. The 9V battery test is odd - in DC it measures 8.5 or -8.5 swapping the leads, so that seems about right. In AC it measures 18.8V with the leads one way, and 0V the other way. I expected about 12V or 13V regardless of which way around the cables were, if it were applying the scaling to get equivalent DC power. I think I'll need to do some proper reading up on multimeters, or maybe buy one that comes with detailed documentation - I'm going around in circles with what I'm understanding of what people are telling me vs what I measured, but thank you for taking the time to try and help me with it!

When I compared with N gauge for controller, track and 7-coach HST, T gauge came out cheaper, and I find N gauge is usually cheaper than OO, and when I've looked at O and Z they've been a lot more expensive. But in real terms T gauge isn't much less expensive even though it's a lot smaller, as you've seen. I don't know the details of the economics of model railways, but I'd certainly have a lot more trains if it was a lot less expensive. Presumably the market demand for toy trains or low-detail models just isn't high enough these days to be viable business for the manufacturers.

@@endoorrailway These companies do not even give young potential hobbyists a chance anymore, there should be a reasonable quality starter set with a bit of everything, scenery some length of track flock, train , trees ect all for under 100 pounds and it , If they were smart would also contain a small catalogue of next steps and teasing pictures of the good stuff to inspire, sure the margins would be tight but this is basic marketing often referred to as a foot in the door. thanks for the reply

It does seem to make logical sense - get people interested when they're young in order to get their business later when they can probably afford more. I have no idea about the economics or how companies measure that eventual pay back, or even if it's possible to measure properly, so I'm neither defending them nor blaming them. As a customer and as a father I do agree it would be good if there were more low-cost options available though, so there was something for everyone. Thanks for the comment 🙂

Thanks for your suggestions - they're helpful 🙂 A comparator or voltage divider sounds good - I'll be having a go with some resistors soon for the divider, and comparators look low-cost so might be worth trying too. Eventually I'll need to fit everything onto a circuit board that fits into a locomotive, so if I can get away with a couple of resistors that seems like it might take up less space than an integrated circuit package. Yes a simple cut-off sounds good - I think the signal is likely to be good most of the time, and since commands are repeated it shouldn't matter if the odd one gets mangled somehow. A couple of other people have mentioned PIO on the Pico - I hadn't come across that before. It does sound good, but ultimately I'm expecting to move to something physically smaller than the RP2040, so I don't want to develop things with things that are too Pico-specific.

@@endoorrailway Regarding resistor dividers, I’d be wary of voltage spikes causing damage to the Pico. To avoid that look for something called a protection diode and put in across the bottom resistor of the pair (assuming you’re powering the Pico from the rails. Between GND and the Gipson pin if not). This will prevent the voltage going higher than the diodes rating (which should the 3.3v here).

Thanks - that's worth knowing about - the DCC specifications for decoders state they should be able to work up to something quite high - I think it's 20 Volts - so I should consider it possible the controller could output that. Spikes could also happen for various reasons, so they're worth defending against if possible.

Yes, it's surprising it exists and works!

I'm not sure what I'd fill it with - what did you have in mind? Although it stands out in scale terms, it's far too small in real terms to put a tiny slice of rail in. Thanks for the hint about torx 🙂 I'll have to see if I can find suitably tiny ones, and maybe buy some smaller screwdrivers.

@@endoorrailway you could try low melt soldering rod, after shielding the sleepers with tin foil. Or you could use jb steelstik, or any other metal epoxy putty. These work at room temp. Push a tiny bit into the gap and use a craft blade to form it into a shape continuous with the rail. Look at micro electronics (particularly fpv) parts. You'll find tiny torx hardware that will be much less likely to strip.

Awesome pointers, thanks 🙂

The tiny scale of T gauge makes it possible to have models of other things that would otherwise take up too much space in the more popular scales, big ships included 🙂

Ants would be about the same size as people at 1:450, so it's just the right size for them 🙂 Not sure which creatures the other scales are for though.

Thanks! Once I'd had the idea, I just had to do it 🙂

Thanks - it took me a lot more effort to make this video than my usual ones because of the diagrams for the explanations, so I'm glad it's making a difference 🙂 I may make my eventual "production" code public on GitHub, but in a way it's a bit pointless because people like you and I want to do it ourselves from scratch anyway 🤣 I too find this daunting though - I'm comfortable with programming, but there's loads that I don't know about the electronics side. But it looks like there's plenty of community help available - I've been given good advice in comments already 🙂

Same here. I'd LOVE to convert all my locos ( 00 not N , thank goodness! ) to DCC, but the cost of loco modules is SOOO expensive, and then of course, the main controller as well.... I'm definitely looking forward to your solution. One question, is it possible to do it this with Arduino, as I have a spare Nano I can use for test purposes? Cheers.

There are other people who've done it on Arduino - the search phrase "DIY DCC decoder" on Google brings back useful results. I read about some of the things linked from dccwiki.com/Do_It_Yourself#Decoders, but not in depth. I'm a long way off anything that can go into locomotive yet, but it looks like other people have done it already 🙂

@@alanclarke4646 IIRC, for the main controller you can use arduino with "DCC++" Although I've never used it myself

From what I read the Pico is 133 Mhz, so to take 30 microseconds to get a reading of the input means it's executed nearly 4,000 instructions! The fact the Arduinos can do all this reliably makes me think that MicroPython is the issue - before long I'll have a go at this with C, just to see the difference. Several other people have also advised that the voltage regulator isn't the way to go, so I'll also see what resistors I've already got and make a voltage divider instead. It would then be interesting to see how the MicroPython does too after that. I'm not expecting to need an oscilloscope for many things, so I'll see how far I can get along without one, but am open to the possibility I'll need to get one. Thanks for the suggestions 🙂

Python is usually interpreted, whereas C++ (as it roughly is) on the Arduino is compiled. So every Python statement has to be read (often copied to an instruction buffer), taken apart, tokenised, parsed and then starts the execution of a fragment of machine code, and then the next part of the statement has to be... yes, you guessed it. I would normally reckon on interpreted code being 20 times slower than compiled code. Compiled programs tell the processor exactly what to do, at full speed. They are, however, tricky to debug, the Arduino IDE and others have a good go at spotting errors at compile time, but after that, the processor will be on its own. There will be some error trapping, for out of memory access, numbers out of range, trying to put values into an input port and so on, but... A good example, I wrote a fractal program in BASIC (interpreted) in 1988 that took 55 minutes to create the Mandelbrot set on screen. I then found a fractal program that did it using compiled machine code in about a minute. The BASIC was, however, good enough for a printer exerciser that wasn't time-crucial.

@@neilbarnett3046 Yeah, I remember thinking when he said it the budget was 100 instructions per microsecond that it would be fine in C or assembler where I'd expect 10 instructions per bit. But if Python is 10x worse that's 100 instructions and very close to being too slow. Python definitely has its uses in data science type applications but running it in a real time embedded system is not one of them. C is great for that sort of thing and if the C compiler does a bad job on the time critical parts you can just write them in a assembler.

@neilbarnett3046, @user-qf6yt3id3w There's some degree of compiling in Python, but I suppose it's more like caching because it's first done at runtime. But that's normal Python - I've not got any idea how MicroPython is implemented. I fully expect interpreted languages to be slower - really I was just having a go with MicroPython to see how it would turn out, and underestimated just how much work it's needing to do to be like standard Python. Eventually I'll get to trying some C on the Pico. Thanks for your comments 🙂

Thank you for your kind words and this useful information 🙂 A few others have also suggested I should use voltage dividers, or other things besides a voltage regulator, so that message is coming through loud and clear, and I'll be doing some component shopping before the next iteration 🙂

@@endoorrailway A voltage regulator is designed to provide a _stable_ supply voltage, so it's not surprising that it doesn't work that well for an intentionally changing signal.

@mrab4222 - thanks, yes I guess that does make sense because it's going to be trying to counteract fluctuations, so that's likely to add some delay even though the voltage is totally dropping off below what the regulator works with. So far my main limiting factor is that it can take a long time for the MicroPython to take a reading of the input, compare it to one that's in memory, and record the time if there's a flip; none of how long that takes is affected by the voltage regulator. The regulator may well affect what happens in the scenarios where I used interrupts though, since they directly hinge off changes in the signal. I'll be moving to C and, for now at least, some resistors for voltage dividing - it looks like I've already got some at resistances that should work 🙂

@@endoorrailway If you already have a bunch of random resistors laying around, you can connect them in parallels or in series to get the required equivalent resistance. This will be sufficient for a quick prototype.

@barmalini Good point, thanks - putting smaller ones in series could be useful if power through them is too high too, though it looks like that's not going to be an issue in this case.

Thanks for the info 🙂 Ah OK - out of curiosity, what makes the regulator so bad for this? I'll definitely need to scale this down though, and I know it's possible to get small surface-mount resistors, presumably also transistors and optocouplers. But wouldn't the resistor approach rely on the track voltage staying the same? In practice it does, but according to the DCC specifications a base station would be allowed to produce a lower voltage, and decoders should be able to cope with it. Plus locos might get poor pickup on occasions even if the track voltage is consistent.

I came here to say the same 🙂 : Nobody uses voltage regs as level shifters. I have not looked at the signal on a scope, but I don't think their startup time/speed will be reliable enough for proper timing. The pico should be plenty fast (I think) for what you are doing. You can try with a resistor divider if you do not want to isolate the track and pico with an optocoupler.

The voltage regulator is not ideal - a step change on the input will result in a slope change on the output. I recommend you use a high speed optocoupler (6N137 is commonly used). This will also protect your PC from any damage. In your final decoder, you can just use a series resistor to limit the current into your microcontroller and rely on its input protection diodes to clip the signal to 3V3 or 5V.

@@endoorrailway I only add some to what colegues wrote. Those regulators work stable when some substantial current is drawn from output and today's microcontroller inputs are not taking current at all almost. Also they have some kind of regulation loop and may became oscilatiors without decopuling and they are not suited for high freqency signals as one write it may generate substantial slopes, especially when load is almost not existent. It may be mitigated partially by pulldown resistor on 3.3v side and some capacitors but sincerely I'm shocked that it works at all 😉

@@CarstenBe about lower voltage - if you do divider 1:4 for example then if input drops 1v then output drops 0.25v also voltage value accepted as logical 1 is quite wide starting from 2V also most microcontrollers will accept more than 3.3v some even 5v without harm, eventually you can add zener diode to for safety. But optocupuler maybe most safe and small solution.

To follow up, averaging RMS meters assume a sine wave amd multiply their measured value by 1.11 to approximate RMS. ( (sqrt(2)/2) / (2/pi) ) So divide by 1.11 to get the average value of your measured signal. Since average and RMS for square are the same, you're done. Should be measuring less than two thirds though, I cant explain that @ 3:55.

Thanks @kokodin5895 and @electrowizard2000 for the information - this afternoon I looked up what RMS is and came to the same conclusion about the square wave, explaining the track output in AC mode. I don't think the multimeter would need to do RMS to measure DC, though - in fact it can't be, else it would never produce a negative reading, so for now I think the two-thirds thing remains a mystery.

@@electrowizard2000 this is not sine though, it is square wave alternating via h bridge from single positive voltage if a meter has small bandwidth even if it is averaging it would measure much less than normal ac, most cheap meters is bandwidth limited to less than 1khz because ac they are ment to measure usually is 50-60 hz, the best way to measure this kind of voltahe is to put full bridge on it and measure dc and better yet use something like texas instruments active bridge rectifier and it would spit out 1/10 of rms voltage as a dc, i made meter like that to measue 14khz pulse voltage used in crt tv's as a heater voltage for the crt