View source for Upgrading a Web based DCC control station

[[Category:Electronics]]  <!-- include this page in the "Electronics" Category! -->

[[Category:Works In Progress]] <span style="color:red;"><br>Under construction/modification by [[User:EricTimberlake|Eric Timberlake]] ([[User talk:EricTimberlake|talk]]) 02:56, 1 May 2023 (PDT)<br>Do not trust anything as "real" just yet!<br></span>

At the April RCGRS MRT SIG meeting, Dr. Geoff Bunza gave a presentation on a '''[https://forum.mrhmag.com/post/an-operating-steam-throttle-you-can-customize-12548356?highlight=steam%20throttle&trail=25 steam locomotive throttle]''' he and others have developed. It requires actual input from the operator to run the locomotive. It is packaged in a clever 3D enclosure with levers for the Johnson bar, speed control, and braking, and a lot of other controls needed for a real steam locomotive.
{{rtoc}}

Dr. Bunza's work leverages the work of '''[http://udelmas.e-monsite.com/pages/centrale-dcc-wifi-d17.html Ulysse Delmas]'''.  The Petite Command Station. 

The concept is this - a DCC command station with a built in web server.  Using ANY tool with a browser and a WiFi connection, you load the control page(s) and can from there control any DCC decoder (locomotive or accessory) attached to the DCC output.  Dr. Bunza uses HTTP post commands from his Steam Throttle to this web server enabled DCC control station.

In Dr. Bunza's presentation to us, the DCC output was attached to a short section of HO track and DCC locomotive control was demonstrated.  The locomotives shown were configured with off the shelf HO scale DCC decoders.

Everyone was quite impressed with all work Dr. Bunza had done..  The G-Scale attendees at the April 2023 MRT SIG meeting were all very excited about the project and the idea of adapting it to G-Scale use.

== Applying to G-Scale ==

For G-Scale applications, we need 3-6 amps of DCC modulated power to run our big locos and loud sound cards.  '''[https://dccwiki.com/Introduction_to_DCC DCC]''' is a protocol describing how to modulate a non-polarized square wave to encode information, aka '''[https://simple.wikipedia.org/wiki/Binary binary]''', or ones and zeros and ''additionally'' the square wave can be rectified to provide power to the equipment (decoder or accessor) in contact with it.  GENERALLY speaking, this non-polarized square wave is transmitted to the train via the track to provide both instructions ''and'' power to a decoder equipped device.  To create this DCC signal, a micro processor wiggles the control lines of an H-Bridge, which simply flips the signal back and forth, not unlike reversing a motor over and over, but VERY FAST..  The H-Bridge component '''has a finite limit''' in terms of allowing current to flow through it. 

The D17 device combines the "wireless gateway" and "control station" and some of the "booster#1" functionality represented in this '''[https://dccwiki.com/Introduction_to_DCC#Overview_of_Digital_Command_Control_System basic DCC diagram]'''.

I volunteered to see about updating the command station end of all this work by Dr. Bunza and others to support a G-Scale sized load, which mostly just means "upsizing" the H-Bridge for more current capacity.

I should be clear on intent here - this is NOT a device intended to power track, it's designed with existing G-Scale DCC decoders just like you'd use an Airwire Converter device for in terms of a battery conversion.  I suspect it WOULD, however, WORK THAT WAY, it's just not my design criteria at all.  The end result would be a battery powered locomotive using an off the shelf DCC decoder and sound card and accessible via a web browser on the same WiFi network to act as the control interface.

== Research ==
[[File:H-bridge-switches.png|thumb|A mechanical H-Bridge]]
The diagram on the right shows the basic theory of an H-Bridge.  Close S1/S4 or S3/S2 to forward or reverse the motor.  DO NOT close S1/S2 or S3/S4 at the same time!  NOT GOOD.  In place of the motor, put the track rails and switch it back and forth fast with a slight variation of speed to represent ones or zeros.  That's how we create a DCC signal that can also provide power.

My first step was to research what this electronic "'''[https://en.wikipedia.org/wiki/H-bridge H-Bridge]'''" thing is and some design theories behind it.  I learned that when using '''[https://en.wikipedia.org/wiki/MOSFET MOSFET]''' transistors as a switch, a thing called "'''[https://en.wikipedia.org/wiki/Gate_capacitance Gate Capacitance]'''" is your enemy..   This isn't a deep electronics lesson, but what I learned is that Gate Capacitance affects the time required to '''TURN OFF''' a typical '''[https://en.wikipedia.org/wiki/MOSFET MOSFET]''' and how if you're not careful with your design process it's easy to turn on BOTH SIDES of the bridge for very brief periods which will lead to overheating and eventual failure of the output stages despite it appearing logically impossible based on the schematic.  This is referred to as "shoot through" and is undesirable.  All this boiled down to this.   ''I'm not smart enough of an electronics guy to solve this problem and create a reliable device.''

Fortunately, I don't have to be.

== Using an existing product for inspiration ==
To advance Dr. Bunza's design to G-Scale, we need to increase the amount of current supplied by the DCC 'control station', which in our case is an ESP32 or ESP8266 WiFi capable micro controller that drives a full H-Bridge to create the non-polarized square wave and encode the DCC commands via the square wave period or frequency..  This means re-designing his very small board designed for HO scale locomotives and layouts into something a LITTLE larger and capable of supporting more current.

I spent ''LOTS'' of time digging through various component SPEC sheets, but then I realized I had an actual example of what I want to do sitting right on my bench..  An '''[http://www.cvpusa.com/airwire_convrtr_series.php#convrtrinfo Airwire 900 CONVERTER-60]''' - the '''EXACT THING''' I want to duplicate, except it's receiving a signal via 900MHz radios vs. WiFi frequencies at 2.4GHz.  It uses a Texas Instruments microprocessor, but that's effectively the only difference.

They use a device called a '''[https://www.digikey.com/en/products/detail/infineon-technologies/BTN8982TAAUMA1/4772017?s=N4IgTCBcDaIEYBcB2AOAnCiBdAvkA BTN8982TA]''' half H-Bridge.  Using two of these devices creates a fully functional H-Bridge like the mechanical diagram above..  More on this device from the '''[https://www.infineon.com/cms/en/product/power/motor-control-ics/brushed-dc-motor-control-ics/single-half-bridge-ics/btn8982ta/ manufacturer, Infineon]'''

Airwire uses a Texas Instruments micro-controller and an off the shelf 900MHz receiver module connected to two BTN8982TA Half Bridge devices together creating a full H-Bridge. so there's not really much to reverse engineer here.  All we're going to do is swap out the Texas Instruments microprocessor with a ESP microprocessor running '''[http://udelmas.e-monsite.com/pages/centrale-dcc-wifi-d17.html Ulysse Delmas]'''' ESP8266 code base that is the web server part I mentioned earlier.

== Sample Application ==
Reading the SPEC sheet for the BTN8982TA, I found this device has built in circuitry to prevent the overlap condition mentioned above, aka "shoot through".   Further reading showed Infineon had done almost all the work for me in terms of a "sample application circuit"!  Talk about helpful!  No shoot through, and a ready made example to leverage!

Here's their '''sample''' schematic intended to teach folks how to apply their device:
*You are NOT expected to understand this - it's just an example of how typical "Application Notes" inform design decisions by people like me who almost know what they are doing..  ;-)

[[File:BTN8982 sample circuit.png|Application Circuit example from Infineon|800px]]

== Adapting to the D17 ESP8266 code ==
So, now I can take all these concepts and start working on a schematic that integrates a '''[https://www.wemos.cc/en/latest/d1/d1_mini.html everyday ESP8266 "Wemos D1 Mini"]''' into a "wifi" web server that outputs DCC capable of up to 6-10 amps or so..  This example application lines up VERY nicely with '''[http://udelmas.e-monsite.com/pages/centrale-dcc-wifi-d17.html Ulysse Delmas]'''' ESP8266 code base for a '''[https://www.ti.com/product/SN754410 754410 half bridge chip]'''..  The inputs of the two BTN8982TA parts is essentially identical.  The 754410 "EN" (enable) input is the same logic as the BTN8982TA "INH" (inhibit) input and the individual H-Bridge halves are identical, it's just the BTN8982TA is capable of (IN THEORY!) 50 amps of current.  Now, we're not getting ANYWHERE near that kind of power capacity here - keep in mind that Airwire uses the SAME PART, but is only rated at 6 Amps continuous.  That's the cost of simple no-heatsink air cooled parts slapped on a very small circuit board like ours. Nowhere for the heat to go, so we're seriously de-rating as a result.

The '''[https://www.digikey.com/en/products/detail/infineon-technologies/BTN8982TAAUMA1/4772017?s=N4IgTCBcDaIEYBcB2AOAnCiBdAvkA BTN8982TA]''' half H-Bridge features an "IS" output or Current (I) Sense (S) ,but we can't really use it:
*No provision for it in the D17 code, and I'm not about to change it...
*The '''[https://www.wemos.cc/en/latest/d1/d1_mini.html Wemos D1 Mini]''' only has one Analog input, and we'd need two, so...

We'll just leave the IS outputs open and forget about that feature for now.

I also skipped the reverse polarity protection in the example like many mfgs, including Airwire - just be careful how you hook it up!

Here's my upgraded D17 schematic.  The '''[https://www.wemos.cc/en/latest/d1/d1_mini.html Wemos D1 Mini]''' runs the web server and handles WiFi as well as having three output pins that control the H-Bridge.  Swiftly switching the H-Bridge back and forth creates our DCC signal.  Using beefy components means the decoder end can rectify that wave form and provide up to six amps of DC power for motion, lights and sound without over heating the control station switch components.  (The H-Bridge part.)

[[File:Proposed D17 upgrade.jpg|Proposed schematic|800px]]

= Make a circuit board =
[[File:Topofheavydutyd17board.png|thumb|alt=Top view of "heavy duty" D17 circuit board|Top view of "heavy duty" D17 circuit board]]
[[File:Bottomofheavydutyd17board.png|thumb|alt=Bottom view of "heavy duty" D17 circuit board|Bottom view of "heavy duty" D17 circuit board]]

Now that we have selected the parts list, or Bill Of Materials, designed a schematic and assigned what is known as a "footprint" to all the parts we can consider trying to craft a circuit board to hold it all...

I use a tool called "'''[https://www.kicad.org/ KiCad]'''" (pronounced "Key-Cad") to first produce the schematic, then using the various inputs, the shape of a device, etc, you can also create a circuit board to hold it all.

I don't do this very often, so it's often a routine of searching the University of You-Tube for how to's that refresh my memory about how to make all this work.

After generating a circuit board, the next step is submitting it to a board fabrication house for actual manufacture.  In my case I prefer to use our own locally owned and operated "'''[https://oshpark.com/ OSH Park]'''", who has made many fine circuit boards for me in the past.

The board ends up being 88.0 mm x 34.0 mm in size and for a run of three each, cost roughly $7.75 each.

Here's a couple of views of the board as it will look after being manufactured to the right of this section.

I ALSO have ordered a few '''[https://www.amazon.com/gp/product/B09SPYY61L/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&th=1 "Wemos D1 Mini" ESP8266 micro controllers]''' from Amazon so I can begin testing the code from '''[http://udelmas.e-monsite.com/pages/centrale-dcc-wifi-d17.html Ulysse's]''' web site on the work bench before final assembly takes place..

= Testing the Code =


TBC - To Be Continued...  Check back soon-ish - or not..  ;-)

--[[User:EricTimberlake|Eric Timberlake]] ([[User talk:EricTimberlake|talk]])