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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Hi, How so?. Hattons are also selling the decoders and by phone or shop orders and users don't have to send Hornby their E-mail address to use the decoders on DCC (which they have to use on DCC at the moment if they are Android users). Regards Nik

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Hi, I did notice when I looked at the waveform from my Gaugemaster LT Rolling road that it appeared to be AC full wave rectified to DC and then a resistive divider driving the base of a darlington pair. If so there is the potential for spikes from the mains side of the transformer to reach the controller output albeit reduced by ~ 19V/240V (the 'sinusoidal' 100hz part of the waveform was up to 19V) . When I looked at the output from a 240v to 12V transformer there were a lot of spikes. I'm not saying this is definitely the cause of HM7000 decoders failing with Gaugemaster controllers. Regards Nik

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