![\"Lewis](\"https:\/\/thenscaler.com\/wp-content\/uploads\/2016\/06\/Age-9-2-weeks-after-back-surgery.jpeg\")
<\/a>Lewis the beagle; 2 weeks after back surgery.<\/p><\/div>\n
Little fellow is recovering and doing well with his rehabilitation program–exercises given to us by the specialty vet. Things like stairs are going to be a problem for him for a while, so he won’t be joining me in the layout room, as he usually does, in the near future.<\/p>\n
Even so, I have some L&NC construction news along with updates on on-going projects.<\/p>\n
<\/p>\n
ACS712 – How Low is Low Current<\/h2>\n![\"ACS712](\"https:\/\/thenscaler.com\/wp-content\/uploads\/2015\/11\/ACS712-Board-150x150.jpg\")
<\/a>ACS712 Board<\/p><\/div>\n
I’ve been exploring the limits of low current sensing with ACS712 sensors. Sparkfun markets a sensor board combining an ACS712 with an OP Amp<\/a> that they characterize as a low current sensor. I had no luck calibrating and using that sensor; if someone reading this has used it successfully, please leave a comment explaining how you calibrate and use it.\u00a0 Additional experiments with Op Amps, including creating a fairly stable instrumentation amplifier, have not been encouraging though I haven’t entirely given up and have a few possible circuit designs yet to try.<\/p>\nThe fundamental constraint with ACS712 sensors is that their output noise inhibits current sensing below 20 mA (officially, Allegro says that you can’t detect below 20 mA without a specially designed version of the chip; which they will happily work on for a paying customer). At higher currents, the sensor works pretty much as advertised and can be used with or without filtering. At and below 20 mA it is difficult to tell the signal from the noise without some sort of mathematical filter; the RMS method I use<\/a> can detect down to around 15 mA with an UNO’s 10 bit ADC.\u00a0 With a Mayhew Labs 14 bit ADC, I seem to get a little more sensitivity, around 12 mA, using the RMS algorithm<\/a>.<\/p>\nBelow 12 mA noise takes over, at least so far as short term measurements go. So I’ve been looking at data collected over longer time periods and have a preliminary method that can discern a low current signal down to around 8 mA.\u00a0 In essence, a low current change causes the long term output noise range to shift up or down depending on whether the current is increasing or decreasing. Capturing this range shift should improve practical detection sensitivity considerably. Its promising, but I still have kinks to work out of the system.<\/p>\n
Is 1 mA sensitivity\u2014the holy grail for detecting a single 10k resistor wheelset\u2014possible with an off-the-shelf ACS712 sensor?<\/strong>\u00a0 Probably not, and that may matter to people who want to use off-the-shelf 10k resistor wheelsets.<\/p>\nThat does not make these inexpensive sensors useless. If you don’t mind making your own resistor wheelsets, then a single 1.5k resistor (assuming one resistor wheelset per car; two wheelsets at 3k\u2014in parallel producing a net 1.5k resistance\u2014one at each end of the car, would be a better idea for a bunch of reasons) will be detectable while still drawing under 1\/10 watt (at 11.5 volts DCC n-scale standard; higher voltages allow for more resistance). 100 wheelsets would draw less than one Amp total current. More on that when I get the system operational.<\/p>\n
Nevertheless, I’m curious whether a 16 bit ADC will help further resolve the low current signal. I’ll be giving that a try this summer so we will see.<\/p>\n
Construction Progress<\/h2>\n![\"Laying](\"https:\/\/thenscaler.com\/wp-content\/uploads\/2016\/07\/laying-trackbed-lower-level-1-150x150.jpg\")
<\/a>Laying Track-Bed at the Red Bluff Yard.<\/p><\/div>\n
I finished drawing in the track plan, including some additional yard space, on the lower level modules and started in on laying roadbed and track.<\/p>\n
![\"Roughed](\"https:\/\/thenscaler.com\/wp-content\/uploads\/2016\/07\/laying-trackbed-lower-level-2-300x199.jpg\")
<\/a>Roughed In Turntable<\/p><\/div>\n
Roughing in the turntable was fairly straight forward. After preliminary rough siting, I installed the roundhouse base and drew in the track center-lines. That located the turntable center (the intersection of the track center lines), enabling me to cut out an appropriately sized circle to accommodate a pit I’ve already created using a plywood base and styrene strips.<\/p>\n
![\"Building](\"https:\/\/thenscaler.com\/wp-content\/uploads\/2016\/07\/pit-under-construction-300x199.jpg\")
<\/a>Building the Turntable Pit with Styrene Strips glued to a plywood base.<\/p><\/div>\n
The turntable project is a major layout item in its own right and will be the subject of multiple future posts.<\/p>\n
![\"Laying](\"https:\/\/thenscaler.com\/wp-content\/uploads\/2016\/07\/Yard-under-construction-300x199.jpg\")
<\/a>Laying Track for the Yard<\/p><\/div>\n
It took a few sessions, but I laid all the lower level track except for the turntable\/roundhouse <\/a>area (which I will do when I install the turntable) and joined it with the helix.<\/p>\n![\"Tracklaying](\"https:\/\/thenscaler.com\/wp-content\/uploads\/2016\/07\/Lower-Level-main-tracklaying-complete-1024x768.jpg\")
<\/a>Track-laying on Lower Level Done.<\/p><\/div>\n
<\/a>ACS712 Board<\/p><\/div>\n
I’ve been exploring the limits of low current sensing with ACS712 sensors. Sparkfun markets a sensor board combining an ACS712 with an OP Amp<\/a> that they characterize as a low current sensor. I had no luck calibrating and using that sensor; if someone reading this has used it successfully, please leave a comment explaining how you calibrate and use it.\u00a0 Additional experiments with Op Amps, including creating a fairly stable instrumentation amplifier, have not been encouraging though I haven’t entirely given up and have a few possible circuit designs yet to try.<\/p>\n The fundamental constraint with ACS712 sensors is that their output noise inhibits current sensing below 20 mA (officially, Allegro says that you can’t detect below 20 mA without a specially designed version of the chip; which they will happily work on for a paying customer). At higher currents, the sensor works pretty much as advertised and can be used with or without filtering. At and below 20 mA it is difficult to tell the signal from the noise without some sort of mathematical filter; the RMS method I use<\/a> can detect down to around 15 mA with an UNO’s 10 bit ADC.\u00a0 With a Mayhew Labs 14 bit ADC, I seem to get a little more sensitivity, around 12 mA, using the RMS algorithm<\/a>.<\/p>\n Below 12 mA noise takes over, at least so far as short term measurements go. So I’ve been looking at data collected over longer time periods and have a preliminary method that can discern a low current signal down to around 8 mA.\u00a0 In essence, a low current change causes the long term output noise range to shift up or down depending on whether the current is increasing or decreasing. Capturing this range shift should improve practical detection sensitivity considerably. Its promising, but I still have kinks to work out of the system.<\/p>\n Is 1 mA sensitivity\u2014the holy grail for detecting a single 10k resistor wheelset\u2014possible with an off-the-shelf ACS712 sensor?<\/strong>\u00a0 Probably not, and that may matter to people who want to use off-the-shelf 10k resistor wheelsets.<\/p>\n That does not make these inexpensive sensors useless. If you don’t mind making your own resistor wheelsets, then a single 1.5k resistor (assuming one resistor wheelset per car; two wheelsets at 3k\u2014in parallel producing a net 1.5k resistance\u2014one at each end of the car, would be a better idea for a bunch of reasons) will be detectable while still drawing under 1\/10 watt (at 11.5 volts DCC n-scale standard; higher voltages allow for more resistance). 100 wheelsets would draw less than one Amp total current. More on that when I get the system operational.<\/p>\n Nevertheless, I’m curious whether a 16 bit ADC will help further resolve the low current signal. I’ll be giving that a try this summer so we will see.<\/p>\n Laying Track-Bed at the Red Bluff Yard.<\/p><\/div>\n I finished drawing in the track plan, including some additional yard space, on the lower level modules and started in on laying roadbed and track.<\/p>\n Roughed In Turntable<\/p><\/div>\n Roughing in the turntable was fairly straight forward. After preliminary rough siting, I installed the roundhouse base and drew in the track center-lines. That located the turntable center (the intersection of the track center lines), enabling me to cut out an appropriately sized circle to accommodate a pit I’ve already created using a plywood base and styrene strips.<\/p>\n Building the Turntable Pit with Styrene Strips glued to a plywood base.<\/p><\/div>\n The turntable project is a major layout item in its own right and will be the subject of multiple future posts.<\/p>\n Laying Track for the Yard<\/p><\/div>\n It took a few sessions, but I laid all the lower level track except for the turntable\/roundhouse <\/a>area (which I will do when I install the turntable) and joined it with the helix.<\/p>\n Track-laying on Lower Level Done.<\/p><\/div>\nConstruction Progress<\/h2>\n
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