chopperaddict Posted January 23, 2017 Share Posted January 23, 2017 Hi Everyone I hope this information might be useful for other modellers out there. I asked about this problem on the Forum, but the only real answers were to be able to send DCC control signals to slow the locos down, a very difficult task. All I want is to be able to "force" a train entering any one of the 7 roads to slow down gently, and then go nearly to the end of the storage road, finally stopping at a given position until released by the operator, using an Arduino to control it all. After quite a bit of experimentation, I discovered that the use of a decent power DIODE would slow the loco/consist down quite considerably. So I decided that all I needed to do was have an Arduino program/Sketch that used 2 IR sensors to identify when the loco entered the storage road, and again when it reached the optimum stopping point. When the loco passes the first sensor, the sketch switches the normal DCC feed sent via one of the relays to a second one containing the above mentioned diode added to the DCC power wire, and then removes the full DCC power from the road. The loco slows nice and gently, and then, when it crosses the second sensor, the relays are switched so that the power sent via the diode feed is also removed from the road, causing the train to stop at the right place. When the operator hits a switch of some type, the sketch reads the input pin for that action and reconnects FULL DCC power to the road, so that the train will return to its previous speed settings using the CV configured acceleration rate as it exits the storage road. The only possible downside of this system is that once the diode feed is in place, the loco will not respond to any more commands you may send to the loco, because the track is only seeing a half wave rectified signal, but I have never found any need to have the loco respond to me while it is doing it's slow down/stop process. Whatever settings you may put into the hand control during this slow down process,at least until the loco enters the STOP position will still be used automatically once power is returned to that road. I welcome comments on this system ? Ian Link to post Share on other sites More sharing options...
Suzie Posted January 23, 2017 Share Posted January 23, 2017 There are few little things that might trip you up. Good decoders will often not notice the effect of the diode. Decoders such as Zimo that have been configured for constant speed regardless of track voltage will just compensate for the apparent lower voltage. Decoders that have a comparator input (most decent decoders) will still see the DCC data on the track, and decoders that use a simple resistor input will see the data when put on the track one way, but not when turned around. Decoders with 'Brake on DC' may well see it as a braking section and slow down according to the configured braking settings and ignore your other arrangements. Decoders with 'DC Analogue' enabled may well see just DC and hurtle off at full speed. If there is no pre-switching section of track long enough to hold the whole train, stock with power pickups may well bridge between your stopping section and the normal DCC track bypassing the diode. Apart from that it may well work. The diode is similar to the method used on analogue layouts to stop trains from hitting the end, but allowing them to reverse out. Your implementation could be extended with a bit of smoothing and protection to properly create a 'Brake on DC' solution but that is a bit old hat now. The modern equivalent is Asymmetric Braking which uses a slightly different arrangement of diodes to achieve a similar result while maintaining full control of the train from DCC. In practice you will probably find it easier to use asymmetric braking (easiest), or possibly Brake on DC (supported on some usually older decoders that don't have asymmetric braking) or a brake signal inserter (works on all decoders) but even then you will still have to take account of some of the above. Link to post Share on other sites More sharing options...
Junctionmad Posted January 29, 2017 Share Posted January 29, 2017 Asymmetric Braking is a Lenz offering , not available on any other decoders as far as Im aware fundamentally and this is a huge failing of the now geriatric NMRA DCC spec, is that there is no cross-decoder method of slowing and then stoping DCC controlled locos . There are various hacks, fiddles and kludges to try and get something to work and everyone of them has drawbacks The only real system is a railcom based ( or other way of discovering the trains DCC address ) and then commanding the speed , based on detecting the trains progress through track section detection . by the way , Im very suprised you are getting a significant change in speed as a result of one diode drop , I wonder have you lenz decoders with the Asymmetric braking feature turned on . ????, what you have done is actually simulated the signalling sequence that triggers the Braking function on Lenz decoders Link to post Share on other sites More sharing options...
RMweb Gold MarshLane Posted January 29, 2017 RMweb Gold Share Posted January 29, 2017 I welcome comments on this system ? Ian Hi Ian, What DCC system and decoders are you actually using for this? Rich Link to post Share on other sites More sharing options...
Suzie Posted January 30, 2017 Share Posted January 30, 2017 Asymmetric Braking is a Lenz offering , not available on any other decoders as far as I'm aware... Asymmetric braking is available on decoders from Lenz, Zimo, Hornby and even ESU now. I am sure there must be more. ...Fundamentally and this is a huge failing of the now geriatric NMRA DCC spec, is that there is no cross-decoder method of slowing and then stopping DCC controlled locos... Not sure about it being defined by the NMRA, but brake on DC is quite widely supported on decoders that do not have asymmetric braking. Link to post Share on other sites More sharing options...
Crosland Posted January 30, 2017 Share Posted January 30, 2017 by the way , Im very suprised you are getting a significant change in speed as a result of one diode drop , I wonder have you lenz decoders with the Asymmetric braking feature turned on . ????, what you have done is actually simulated the signalling sequence that triggers the Braking function on Lenz decoders This is not DC, so it's not "one diode drop". DCC is AC and the diode blocks conduction in one direction completely. The DCC is being half-wave rectified with the effect that the loco sees only half the track voltage. As Suzie says, exactly what happens will depend on the design of the decoder. Link to post Share on other sites More sharing options...
Talltim Posted January 30, 2017 Share Posted January 30, 2017 I'm not fully conversant with the way DCC control signals are sent and how long they are in comparison to AC wavelength . Is it possible that if you lose half of the AC wave parts of the control signals get dropped and thus you lose control? Obviously I understand that you probably wouldn't be controlling a train into an auto slowdown/stop section, but presumably you'd still want the emergency 'stop everything' function to work? Link to post Share on other sites More sharing options...
Suzie Posted January 30, 2017 Share Posted January 30, 2017 DCC signal is aroung 10000Hz compared to industrial frequency mains AC which is 50Hz or 60Hz. Each bit of data is sent as either as a '1' bit with a short pulse of positive then negative, or a '0' bit with a long pulse of positive then negative. If the train is on the track the other way round it will see the half bits in the reverse order. NMRA spec is quite loose on how decoders recieve the data, and a lot of older and cheaper (especially American) decoders only look at either the positive or the negative half bits and ignore the others (depending on which way the train is facing). If you are going to slow or stop a train it is best to send a recognised stop/slow signal using one of the recognised methods to ensure that the train will either stop or remain under control. If using diodes it is important to use diodes that will work at 10KHz Link to post Share on other sites More sharing options...
Crosland Posted January 31, 2017 Share Posted January 31, 2017 Is it possible that if you lose half of the AC wave parts of the control signals get dropped and thus you lose control? As has been stated twice before, it depends on the design of the decoder. It is possible to decode the data from a half wave rectified DCC. Link to post Share on other sites More sharing options...
chopperaddict Posted February 4, 2017 Author Share Posted February 4, 2017 Thanks for your feedback Suzie. I agree with you, it is less than optimum, but works with my Fleischman and Roco locos, many using gaugemaster decoders, but others are in use as well. So far none have not behaved as per my description. I did not know about the Brake on DC option, so will certainly check that out by going through all of my decoders documentation ! (RTFM still rules eh ?) Cheers Ian Link to post Share on other sites More sharing options...
chopperaddict Posted February 4, 2017 Author Share Posted February 4, 2017 There is: the general brake command. Speed 0 on the general address. It was the only method prior to 'brake on DC' and the ATLplus system (Lenz nicked the ATLplus system and renamed it ABC, but in essence is the same. I can prove this!) What is the actual "name" of this general brake command exactly, it sounds like that might solve my problem ? Link to post Share on other sites More sharing options...
chopperaddict Posted February 4, 2017 Author Share Posted February 4, 2017 As has been stated twice before, it depends on the design of the decoder. It is possible to decode the data from a half wave rectified DCC. I did try putting the diode on either track t see if that had any effect on control, but both ways I loose control of the train. Can you explain how I could get my locos to decode data from my half waves ? Link to post Share on other sites More sharing options...
chopperaddict Posted February 4, 2017 Author Share Posted February 4, 2017 DCC signal is aroung 10000Hz compared to industrial frequency mains AC which is 50Hz or 60Hz. Each bit of data is sent as either as a '1' bit with a short pulse of positive then negative, or a '0' bit with a long pulse of positive then negative. If the train is on the track the other way round it will see the half bits in the reverse order. NMRA spec is quite loose on how decoders recieve the data, and a lot of older and cheaper (especially American) decoders only look at either the positive or the negative half bits and ignore the others (depending on which way the train is facing). If you are going to slow or stop a train it is best to send a recognised stop/slow signal using one of the recognised methods to ensure that the train will either stop or remain under control. If using diodes it is important to use diodes that will work at 10KHz You mention "the recognised methods to ensure that the train will either stop or remain under control.". Can you expand on that as to exactly what they are, and how to implement them ? Link to post Share on other sites More sharing options...
chopperaddict Posted February 4, 2017 Author Share Posted February 4, 2017 I'm not fully conversant with the way DCC control signals are sent and how long they are in comparison to AC wavelength . Is it possible that if you lose half of the AC wave parts of the control signals get dropped and thus you lose control? Obviously I understand that you probably wouldn't be controlling a train into an auto slowdown/stop section, but presumably you'd still want the emergency 'stop everything' function to work? I would agree, but I do have a very easy to access "big red switch", that kills all DCC power to the entire layout - JIC Link to post Share on other sites More sharing options...
chopperaddict Posted February 4, 2017 Author Share Posted February 4, 2017 Hi Ian, What DCC system and decoders are you actually using for this? Rich I am using the Gaugemaster Prodigy Advanced system, with various different, but all reasonable quality decoders. I wanted to experiment a bit with different types of decoders to be able to decide which one I will eventually settle on for all locos.after testing each of them. Link to post Share on other sites More sharing options...
chopperaddict Posted February 4, 2017 Author Share Posted February 4, 2017 ... by the way , Im very suprised you are getting a significant change in speed as a result of one diode drop , I wonder have you lenz decoders with the Asymmetric braking feature turned on . ????, what you have done is actually simulated the signalling sequence that triggers the Braking function on Lenz decoders Strangely, So am I, but I initially tried several isolated sections, adding more diodes to each one to get progressive slow down. However, the extra diodes seemed to do very little in terms of changing the slowed down speed. Even with a total of 5 identical diodes (in series) there was little difference. Maybe putting them in parallel would work ???? Link to post Share on other sites More sharing options...
chopperaddict Posted February 4, 2017 Author Share Posted February 4, 2017 .....what you have done is actually simulated the signalling sequence that triggers the Braking function on Lenz decoders Interesting comment, except that the locos do not slow down to stop in the diode fed section, they only slow down, but carry on at the slower speed until I trigger the power cut to bring them to a halt ? Not ideal at all, as I would like the lighting etc to continue functioning, but then again,for this particular purpose, the trains are hidden underneath the station boards. Link to post Share on other sites More sharing options...
Suzie Posted February 4, 2017 Share Posted February 4, 2017 You mention "the recognised methods to ensure that the train will either stop or remain under control.". Can you expand on that as to exactly what they are, and how to implement them ? The three general methods are: Brake signal insertion (sending speed step zero as a broadcast to all locos) using a brake signal inserter on an isolated section of track. Typical example is the Lenz LG100 module. Brake on DC where nominal 12VDC in the reverse of the direction of travel is applied to an isolated section of track. Asymmetric braking where the amplitude of one half of the DCC waveform is reduced. Typically by a Lenz BM1 module. With the brake signal insertion care has to be made to ensure that there is no bridging between the braking section and the rest of the layout. Brake on DC is similar. Link to post Share on other sites More sharing options...
Nigelcliffe Posted February 5, 2017 Share Posted February 5, 2017 The three general methods are: Brake signal insertion (sending speed step zero as a broadcast to all locos) using a brake signal inserter on an isolated section of track. Typical example is the Lenz LG100 module. Brake on DC where nominal 12VDC in the reverse of the direction of travel is applied to an isolated section of track. Asymmetric braking where the amplitude of one half of the DCC waveform is reduced. Typically by a Lenz BM1 module. With the brake signal insertion care has to be made to ensure that there is no bridging between the braking section and the rest of the layout. Brake on DC is similar. mostly agree. With brake signal insertion, yes extreme care on bridging. With brake-on-DC, it depends on where the source of DC comes from. With independently powered DC (typical use) yes, bridging of DC to DCC needs to be avoided. But there are brake-on-DC solutions which use the DCC as the power source, see "bogobit.de" for example. Link to post Share on other sites More sharing options...
chopperaddict Posted February 6, 2017 Author Share Posted February 6, 2017 Brake signal insertion (sending speed step zero as a broadcast to all locos) using a brake signal inserter on an isolated section of track. Typical example is the Lenz LG100 module. Thanks for the suggestions Suzie, but around £51 per storage track will total £400 for my needs - far to much cash I fear... :-((((( Link to post Share on other sites More sharing options...
Suzie Posted February 6, 2017 Share Posted February 6, 2017 You only need one LG100, you just feed it into all the areas that require braking. Link to post Share on other sites More sharing options...
Crosland Posted February 6, 2017 Share Posted February 6, 2017 I did try putting the diode on either track t see if that had any effect on control, but both ways I loose control of the train. Can you explain how I could get my locos to decode data from my half waves ? How many times does it need saying? ***It depends on the design of the decoder*** If it doesn't work with your decoder, then it doesn't work with your decoder. Link to post Share on other sites More sharing options...
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