NIK

Hi, Some DCC decoders offer a shuttle facility triggered by Asymmetric DCC. This has the advantage that if you ever want in future to connect your shuttle line to the rest of the layout you can. Also it can be easier to swap from one shuttle loco to another. Some DCC shuttle modules have limited current capacity so may not be suitable for all locos. Regards Nick

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Hi, What would the circuit breaker do and how long would it take to operate?. Regards Nik

Hi, There will probably a small circuit that connects before the rectifier and the stay alive capacitor that takes the DCC signal and converts it to a logic level signal connected to one of the decoders microcontroller input pins. Most stay-alives are sensitive to being overvolted and also normally have a medium resistance path back to the rectifier output so the stay alive will probably not be able to protect the decoder from voltage spikes. Regards Nik

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Hi, I don't know if the following is relevant to problems some folks have been having downloading sounds to the decoders. I've just been testing a DCC loco that's been sitting in a closed box for six months since the last club open day. I found to check its DCC address I had to hold the loco quite firmly down on the test track a number of times before I could read or write CVs. I guess its down to the wheel/track interface or the axle pickups not providing a good enough electrical path. Once I'd checked what address was right it gradually started to move until it was 'normal'. Might be worth putting something soft but not conductive over a loco to weigh it down on to the track (heavy cushion?) during downloading to the HM7000 sound decoder. Regards Nick

Hi, The scenic boards of Beggarwood are back and running in time for our clubs next open day in Basingstoke on Sunday the 23rd April (search for BNHMRS). The DCC points decoders accidently got reprogrammed with the wrong addresses and it took a while to sort things out again. A number of point servo mounts which failed after the hot weather in the summer have been replaced with Dingo servo mounts, some from Santa's Globetrotting Vacation from the Channel 5 competition - we couldn't get a buyer for it so its been dismantled for parts. More scenic details have been added to the layout and the drop on section with the housing estate screwed down. The club's exhibition in March did amazingly well despite the food for catering going up in price - we should have enough to pay the electric heating bill. Nick Murphy (on behalf of the Basingstoke and North Hants Model Railway Society - still looking for members)

Hi, I hoped they were just out of stock temporarily due to chipaggedon. Maybe demand will go up now that Hornby are doing more non Railcom decoders. Regards Nick

Hi, You should be able to add a Railcom transmitter module to a HM7000 fitted loco as you can to any non Railcom fitted DCC loco. However its extra cost and space. Regards Nik

Hi, Just managed to change the sim in time - with full wave rectified 12 volts the resistance mat needed to be about three quarters of the way to max before a 3.3V MCU would get the full 3.3V. I'm not sure what would happen with PWM DC controllers when the loco has bad pickups - the MCU might be overvolted many times a second. Regards Nik

Hi Keith, I will try some time, that I'm about to join a MERG Zoom meeting on RFID for model railways. Regards Nick

Hi Spamcan61, I've just changed my simulation to a smoothed DC supply with a resistance mat as the 'control' element. It depends on the resistance of the loco motor but for a motor drawing 0.5A at 12V the resistance mat needed to be about halfway to minimum resistance before the microcontroller got enough volts to function fully (assuming 3.3 volts). No sign of overvolting as the voltage regulator is getting more or less what it expected. It would be worse for a 5V microcontroller as used in many DCC decoders (providing it needed 5V to operate). I don't know if microcontrollers do much when the DC voltage is low - perhaps the H bridge drive circuits are wired to default to DC drive at low voltages or at all DC voltages. Regards Nick

Hi, I don't know if this is pertinent to the HM7000 sound decoders failing but in trying to answer Pteremy's question I decided to try and simulate the power supply part of a DCC decoder. Using a program called LTspice which is provided by one of the more established analogue semiconductor manufacturers I found the voltage regulators I tried for supplying the microcontroller malfunctioned when fed with PWM. I tried a challenging case of a 10% duty cycle. The output from the voltage regulator collapsed every cycle at PWM repetition rates from 100Hz to 2kHz. That was to be expected. This could mean the microcontroller would be reset every cycle. However in addition the voltage regulator output went up to 6.6 volts which is over its specification and also over the maximum for a 5V microcontroller. I then tried a voltage regulator rated for 3.3V in order to simulate the supply to a 3.3 volt microcontroller which Hornby might have used in their HM7000 decoders. The output voltage went up to 5.4 volts at 100Hz rep rate, way beyond the rating of a typical 3.3V microcontroller. Going to 2kHz rep rate the output voltage went up to 8V. I started with a 50uF reservoir capacitor and then went up to a 220uF capacitor more typical of a sound fitted decoder. With 100Hz rep rate the output voltage stayed for longer during the cycle but stayed over 3.3V for 50% of the cycle. Things were better with a 2kHz rep rate but still the voltage stayed over 3.3V for 20ms. Going to a 90% duty cycle at a 100Hz rep rate made the overvoltages less but took 180ms before the regulator came back to 3.3V output. Going to 100% duty cycle the voltage regulator behaved impeccably as would be expected. I went for a worst case of a loco motor drawing 1A at 12V. Going to a 0.5A motor the regulator was overvoltage for only 20ms at 10% duty cycle at 100Hz rep rate.. All the above is based on assumptions about how the decoder power supply is designed. Regards Nick

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Hi, I got 450ma @12V DC with one Ist batch Dapol OO 74 and 600ma @12V DC with another. I think my Dapol Class 121 DMU was similar. A long way from the Bachmann LMS Crab with 140ma @12V DC (the lowest current consumption loco @ 12V I've measured so far). All tests on Gaugemaster LT rolling road. Higher currents when switching directly from 0V to 12V. I think all my Ist batch Dapol O 73s had wiring faults (and Lime Green 'yellow' warning ends). Regards Nick

Hi, StaRFIshRail has a number of interfaces including Ethernet which I've used briefly with JMRI. I've used StaRFIshRail with MERG CBUS via a MERG CANUSB4. The tags are 6 x 9mm and the vertical range with the smaller of the two aerials they sell is 30mm. Top speed is 125mph in O. StaRFIshRail is said to have MQTT but I haven't tried that yet. Regards Nik

Hi, You may need to check that your DCC command station will allow the computer software to override operators cabs. Otherwise train protection can be instantly overridden when the operator tries to raise the speed again. Regards Nick

Hi, StaRFIshRail RFID should be reliable enough and works with JMRI. Regards Nick

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Hi, Hornby have only done the launch of HM7000, so just as there are only a few TT:120 locos announced at launch there are only a few HM7000 options at launch plus the decoders are designed to work without a DCC command station. If Hornby stop supplying TTS decoders in the future that is unhelpful, as it would be if the stop supplying them now. Regards Nik

Hi, Possibly 6.5mm birch ply top with 5mm standard ply >=6" deep uprights and 2*6.5mm vertical track ends. Uprights at least every 12 inches in X and Y. The club layout I help with uses these and 12 years on and no sign of warping. There is variation in the level of the baseboard tops but that is due to the accuracy the uprights were originally cut to with a jig saw. Beggarwood Lane = a Basingstoke club OO finescale layout. A four foot by 3 foot board could be lifted with one finger (prior to adding track, wiring and scenery). The layout is stored in a hut that varies from sub dew point to high summer SE UK temperatures. I don't think laser cut baseboards will improve things unless they improve the precision that wood joints align to. Laser cut baseboards tend to use MDF whose long term properties in variable humidity conditions are yet to be determined. Regards Nik

Hi, Yes the DCC80 is relay based and I think the Tam Valley unit is electronic. If a DCC command station has a fast current trip (such as the Bachmann Dynamis) it may trip before the frog juicer. If a loco hesitates over a frog switched by a DCC80 then either the relay is in the process of switching or it hasn't switched and the voltage on the track has collapsed due to an excess current being drawn. Regards Nik

Hi, Hornby are a commercial company. They have had financial difficulties in the past, one of which resulted in 50% of the model range being removed from the catalogue. If they think they can do better for themselves by not publishing their Bluetooth feature's protocol then that is up to them. Maybe as Bluetooth is RF and thus can be intercepted forces them to reduce the risk of loco or layout hijacking then things get more complicated. I've had a large club layout hijacked by a club member after we added a Wifi control option and I didn't find it pleasant. Regards Nik

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