# BeagleBone releasing soon (finally) Rev A3 production



## VictorSpear (Oct 19, 2011)

About the size of an Altoid Mint box*, **Beaglebone *from beagleboard.org should be releasing the production Rev A3 version about the same time as the Raspberry Pi is expected. Isn't this *coincidental *or what ? Hobbyists, trains, robots and planes clubs should be excited that the Linux based MCU with support for both Linux (Angstrom) and Android is finally making its long awaited appearance. With Radio Shack promising delivery of Arduino Uno 3 kits, there should be plenty of interest in comparing this with the Bone and with all the other MCU offerings out there. 

The Bone contains the 720 Mhz Cortex A8 AM3359 with 256 Mb of memory and should be retailing around $89 compared to the 128 Mb $25 Pi. You do get what you pay for. There are 2 Enhanced Hi Res PWM, 2GB microSD included, Industry standard 3.3V I/Os on the expansion headers with easy-to-use 0.1" spacing, on-Chip Ethernet ..I2C, UART, SPI, 12-bit ADC and CAN..Worth taking a solid look at for those contemplating OBCs and computational intelligence in their engines. Short Video Clip Here.



Cheers,
Victor


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## Scottychaos (Jan 2, 2008)

Could someone please translate Victors post into English?  
im curious what this is about..but right now I haven't a clue..even after watching the video.. 
what are we talking about? 

thanks, 
Scot


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## VictorSpear (Oct 19, 2011)

In English ? Perhaps this might help....Just kidding of course









We are discussing here possible candidates for embedding something more intelligent than a $100 decoder into a model train. This really would usually interest only those seeking alternative (and perhaps higher) forms of Command & Control/Command with Control like the Napoleonic or Eisenhower methods.....versus DCC....JMRI+DCC..etc..


Cheers,
Victor


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## TonyWalsham (Jan 2, 2008)

I think I can smell a DCC - v - ? war coming on.









Thankfully there won't be regular battery R/C involved.


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## Greg Elmassian (Jan 3, 2008)

Nice development tool for the TI chip. 

Could not find the PWM power specs, probably not enough to drive our loco motors. 

Could not find easy wireless, but I suppose someone will interface something though USB 

Pretty big. 

The part I keep missing is the sound part, the remote control of a motor and a couple of lights is easy. 

Greg


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## VictorSpear (Oct 19, 2011)

Finally a 'Made in USA' product with profuse and readable technical documentation (the TI Sitara chip, I mean, which is a Sanskrit word for 'evening star'). The ePWM subs-system documentation is certainly interesting (Pgs 1918-2079) along with the eCAP module capability (Pg 2062). The fine grain modulation control for brushless motors with pre-scaler event triggers are intriguing. There's a visible difference now in terms of what open-source hardware means. I really can't get anything like this info on the Raspberry Pi chip ( Broadcom BCM2835 Soc).

With many 'capes' (like the Arduino Shields) expected out 'shortly', Adafruit has prepped a board for the experimenter to build their own *capes*. Yes, one would need a separate motor controller with high current handling - It would be great to see a cape arrive shortly with something like the low-cost DRV8814 (2.5A peak, 1.75 A RMS Dual brushed motors) all pluggable and ready to go.

The sound interface should be handled by another pluggable cape with the ALSA open architecture, opening up several sound cards. This way upgrades are matched to needs. A low cost USB stereo one is sighted in this list. The Pi has built-in sound but I don't want to be stuck with just that. I'm hoping the Bone will eventually sell under $49 if it is going to attract the masses of experimenters.

Cheers
Victor


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## Greg Elmassian (Jan 3, 2008)

To keep up with state of the art, you want BEMF sensing, and you need an algorithm that allows decoding more than one motor in parallel. It's not trivial. 

Then once you have this data, you have load information that can be used for the obvious motor control, and the load-dependent sounds (and if you are really smart you can tell that one motor is slipping or taking too much of the load, i.e. something is wrong). 

Sound is still the really tricky part, having a number of loops stored, and a nice algorithm that does not just simply increase the volume, but does things like switch sounds for different loads, and/or can add pre-programmed equalization. 

Think of how the sound of a chuff changes from low to high speed, and from light to heavy load... it's not trivial. 

Greg


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## VictorSpear (Oct 19, 2011)

I was a huge fan of sensor less Back EMF measurement for *velocity *sensing but recently I've been having better results for position+*velocity*+direction+coasting sensing with dual channel Quadrature Optical Encoders assembled under $11 when wheel slip is apparently occurring as compared to imputing it from the electromotive-force measurements. I just need to outperform Bernd Lenz's Gold decoder now 

When coupled with current feedback and velocity feedback sensing, Chuff synchronization (as well as screech/braking sounds and other hisses) should definitely be on the top of any modeler's list !

Cheers
Victor


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## VictorSpear (Oct 19, 2011)

Tony,

Your sense of smell (olfactory) is more advanced than the Beagle looking for his Bone even with his cape  But if you used your peripheral 'vision' sensor occasionally when the blazing sunlight Down Under permits, you might notice that the power draw of the device we are discussing here is *under 2W*. So why then would you not use a battery ? 

Cheers
Victor


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## TonyWalsham (Jan 2, 2008)

I would use a battery. 
Just that any discussions that become, how shall we say, heated, are usually between DCC and R/C battery power. 
I cannot see that being the case here. Rather it will be DCC - v - ?


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## Greg Elmassian (Jan 3, 2008)

Victor, how are you using velocity to determine actual load? 

I'm also confused about your comment on wheel slip... how can you tell wheel slip other than a sudden rise in speed, or comparing two different axles? 

Greg


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## Del Tapparo (Jan 4, 2008)

BS is often confusing.







@import url(/providers/htmleditorproviders/cehtmleditorprovider/dnngeneral.css);


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## TonyWalsham (Jan 2, 2008)

Wouldn't wheel slip give you a sudden (but maybe only slight) drop in speed?


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## Greg Elmassian (Jan 3, 2008)

Hard to determine the difference between wheel slip, momentary change in mechanical resistance, etc. 

Wheel slip is not something that most designs care about, normally only happens in overload condition and the operator usually knows what is going on. 

Greg


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## VictorSpear (Oct 19, 2011)

I'm using a high side current sensing filter for actual load fluctuation, not velocity. For wheel slip detection I'm using two E4P Mini Optical Kit Encoders on two shaft Buehlers (GG211). When there is a momentary difference of more than 2% in any of the velocity reading, I'm attributing it to wheel slip. What else can it be ?


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## Greg Elmassian (Jan 3, 2008)

Umm... it could be what I already said... but I'm not really interested in wheel slip, I'm more basic, low speed control and load sensing... 

Why would you want to use high side control? Even in large scale physical size and thermal considerations are important, as well as current drain, realize the very low impedance of most G scale motors. 

Greg


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## VictorSpear (Oct 19, 2011)

Yes, very interesting debates can be had on high-side versus low-side load sensing. The characteristics are naturally different for both use cases. On the high side, you can use a difference amplifier or a current-sense amplifier. Most decoder suppliers (if not all) are sensing the low-side as they expect the command station to perform the overload reactions.
During high torque conditions approach stall/near stall torque (particularly in high payload at slow speed approaching to dead stop then re-start) and in conjunction with the velocity signal, the high side current sense amplifier during high load pulses is my best indicator. 
When a ground short occurs, it is invaluable. 
When you have an on board battery (or intelligent on-board track/battery) and need to react and protect the embedded components *and *the motors during bus-to-ground shorts or high stall current, it is also more than necessary. While the low side current sensing is okay, its characteristics also don't scale when temperature increases.
So if you look at 1 through 5, I'd be interested in knowing how you would combine short circuit, overcurrent, low speed, temporary wheel slip *and *high temperature feedback on the low side ? I'm using Analog's AD8217 or TI's INA2312 for different conditions - one where the payload is unknown from remotely - as my friends have a fascination with attaching the maximum number of cars to see 'what happens' when I'm not looking.
Also, please take a look specifically at *Maxim's MAX4372F* (under $5) characteristics with Voltage Output 
Cheers
Victor


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## Greg Elmassian (Jan 3, 2008)

Hmm.. you contrast high side vs. low using a difference amp (by which you must mean voltage?) or a current sense amp.... 

I don't get it, you have to current sense, via a load resistor, and you measure the voltage. What is a "current sense" amp? Aren't you still measuring the voltage drop across a low value resistor? 

Isn't this the definition of high side load sensing? (I'm looking for a yes or no answer here) 

I see a completely different comparison between high side and low side.... 

So, items 2, 3, 4 are the support for high side over low side (looking for a yes or no here) 

I'm not even getting past the first couple of sentences of your posts before what you say stops making sense to me. 

It's almost like the post is an amalgam of googled references... 

Greg


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## rmcintir (Apr 24, 2009)

I was too lazy to reinvent the "Back EMF current sense" wheel and just took advantage of what the vendor's circuitry in the LMD18200T, VNH2SP30 and VNH5019 H bridges provide for current sense. The vendor's built-in circuitry is; integrated, reliable, and accurate. Actually I still need to fully test the VNH5019 to make sure it completely works but haven't encountered any problems yet. It is amazingly simple to configure all of them to read Back EMF current instead of supplied current at any given instance. It is quite accurate, assuming you set up a routine on power up to take a baseline for each individual chip. The same routine configures all three chips. Heck, I even got "cruise control" to work but didn't have enough room in the 16F88 for the additional code (nor the desire to actually use it, even if it is WAY COOL!). Using a faster, dedicated processor with a faster A/D circuit will give even better results. The 16F88 isn't exactly fast nowadays, but it is cheap and very easy to work with.


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## VictorSpear (Oct 19, 2011)

Greg,

Ok, if you prefer Boolean responses 

_What is a current sense amp ?_
Operational Amplifier with matched resistors = Difference amplifier whereas Current sense amplifier => Specialized Difference amplifier (Integrated circuit with precision matched shunt resistors)
A current sense amplifier can be used with very small voltage differentials (typically in the order of microvolts)

_ "Hmm.. you contrast high side vs. low using a difference amp (by which you must mean voltage?) or a current sense amp...."_
Hmm ...No. You can use *both *amplifiers on the high side itself. My sentence reads: *On the high side*, you can use a difference amplifier *or* a current-sense amplifier.

Isn't this the definition of high side load sensing? - No. I'd be happy to elaborate. 

So, items 2, 3, 4 are the support for high side over low side - Yes.

"I'm not even getting past the first couple of sentences of your posts before what you say stops making sense to me"

I can understand this. The topic (Current sensing implementations on high versus low side) is non-trivial. (Some manufacturers do not understand or want to understand this. They provide meltable cartridge fuses in their offerings with a 1 year warranty ! They are the first to dismiss anything that doesn't fit their offering. Whilst, others are offering a 10 year warranty on their product - no questions asked, no answers given - simply a full replacement. 


"It's almost like the post is an amalgam of googled references...
"When 'we' diverted into the Back EMF siding from the 'Beaglebone characteristics' - the subject of the post, I find the best way to return while still discussing other things is with precise real-world references to the actual electronics that support the argument from practice and experimentation. The best way to stay on the topic is to link to the real-world usage reference and let the reader decide whether they want to read that. 

So here is the traversal that happened in the post: From 'Beaglebone arrives' ->Back EMF sensing -> Velocity sensing -> Load sensing -> High side current sensing + Velocity sensing .......return to Beaglebone ?

Yes. It can be confusing at times.

Cheers
Victor


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## VictorSpear (Oct 19, 2011)

rmcintir,

If I remember the LMD18200 series from National came out in 1997 ? It had built-in thermal sensing and current sensing and was
considered very futuristic. The other two are quite popular but recently in the last two years there have been significant improvements
in cost/performance/function. The voltage offset can be of the order of 5 micro V today.

If you remember in the eighties, many computer labs used high speed matrix printers where the stepper motor would jam with the paper and overheat,
and you had a smoke fire in the lab. I see some parallels where model trains are on combustible track (leaves, debris) along with water, snow
and other ground-short enablers. Wires do get burnt, devices overheat. At slow speed some decoder manufacturers expect the Back EMF function turned off, others cannot handle it during a consist.

Interpreting back EMF alone by itself for corrective action has its risks in harsh environments where faults to ground can occur at any time. As in model train layouts.


Cheers
Victor


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## rmcintir (Apr 24, 2009)

The chips I chose can all be used to safely measure Back EMF with no external circuitry. They also all have varying degrees of thermal, short, and over voltage protection. So far it has worked well, for very slow speed, on locos configured for track or battery and 1-4 motors. One day I may get a wild hair and add a cruise control function but I haven't had time. I do like pulling a long string of heavy cars at extremely slow speeds.


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## VictorSpear (Oct 19, 2011)

...Arrived last week. Rev A4


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