+When cover is closed, it blocks PCB movement:
+
+[[file:body%20and%20covers/cover.png]]
+
+There is still some empty space inside, so why not add dummy cover on
+top that can be replaced later with add-on functionality/expansion
+board/terminal :)
+
+[[file:body%20and%20covers/cover%20cover.png]]
+
+Download:
++ [[file:body%20and%20covers/body.stl][Body STL file]]
++ [[file:body%20and%20covers/cover.stl][Big cover STL file]]
++ [[file:body%20and%20covers/cover%20cover.stl][Small dummy cover on top, STL file]]
++ [[file:body%20and%20covers/body%20and%20covers.FCStd][Body and covers FreeCAD project]]
+
+* Transformer and AC to DC converter
+
+This is where high voltage from mains electricity enters the system.
+
+Schematic:
+[[file:transformer%20and%20AC%20DC%20converter%20board/schematic.png]]
+
+For safety I kept high voltage section as minimal as possible. That
+is, wall plug runs straight into transformer. Also I used [[https://www.amazon.de/gp/product/B07VGQKM3G/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1][UV hardening
+glue]] for extra safety and isolation on PCB.
+
+Power on/off switch operates on already reduced voltage of about 30
+volts. Power switch is located on [[id:c9a69490-f920-4a31-b32e-b101bfc3d01b][indicator panel]].
+
+[[file:transformer%20and%20AC%20DC%20converter%20board/make,%201.png]]
+
+DC current of about 30 volts is then routed to [[id:65d68227-4bf2-4c4f-b4d3-c390bc6a9c34][Main board]].
+
+[[file:transformer%20and%20AC%20DC%20converter%20board/make,%202.png]]
+
+[[https://www.amazon.de/gp/product/B07RLQH5TR/ref=ppx_yo_dt_b_asin_title_o07_s00?ie=UTF8&psc=1][Single sided prototype PCB is used]].
+
+* Main board
+:PROPERTIES:
+:ID: 65d68227-4bf2-4c4f-b4d3-c390bc6a9c34
+:END:
+
+This is logically main board because it appears to be central hub that
+connects all components. It also houses 2 [[https://www.amazon.de/gp/product/B072MQYJ93/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1][adjustable DC-DC Step Down
+voltage converters]].
+
+[[file:main%20board/main%20board,%201.png]]
+
+High-level schematic of entire device:
+[[file:main%20board/schematic.png]]
+
+As seen from schematic, ~30 volts DC from transformer board is routed
+into first step-down converter that reduces it to about 15V. Reduced
+voltage is then directed to [[id:afc22d23-9bc4-421c-9cac-e0ce34bd36bc][Current limiter circuit]]. Current limiter
+loses about 2 volts. Now we have current and voltage limited power at
+about 13 volts. This power is used to charge connected 12V Lead-Acid
+battery. Also the same power is routed to [[id:e33940bd-652f-4ec0-b53b-1c03e16941c8][connector terminal]] to be
+consumed by connected devices.
+
+As seen from this schematic, device is not meant to provide high
+current for long periods of time. Instead it gets comparatively
+limited current to charge the battery and feed devices with low
+current requirements. Occasional current spikes are backed up by
+battery that stays in use-changing mode.
+
+Also about 13V output voltage is approximate and depends on connected
+battery charge level.
+
+Second Step-Down converter reduces voltage even further to quite
+precisely 5V DC. This resulting voltage is also routed to [[id:e33940bd-652f-4ec0-b53b-1c03e16941c8][connector
+terminal]].
+
+Both 13V and 5V lines are also routed to [[id:c9a69490-f920-4a31-b32e-b101bfc3d01b][indicator panel]] for
+monitoring.
+
+There is single on/off switch. In off position, it disconnects battery
+and transformer from the system effectively powering everything down.
+
+On schematic above, some wires are annotated with numbers from 1
+to 13. This corresponds to output pins on the board.
+
+[[file:main%20board/main%20board,%202.png]]
+* Current limiter
+:PROPERTIES:
+:ID: afc22d23-9bc4-421c-9cac-e0ce34bd36bc
+:END:
+
+Schematic:
+[[file:current%20limiter/schematic.png]]
+
+Simple LM317 based current limiter is used. I used 4.7 ohm
+resistor. It provides about 265 milliamps of current. See [[http://www.reuk.co.uk/wordpress/electric-circuit/lm317-current-calculator/][calculator]].
+
+[[file:current%20limiter/current%20limiter,%201.png]]
+
+Thermal paste below and UV hardening glue on top is used to attach
+LM317 to the heatsink. There is also jumper-like solution on top
+right. This is handy to attach multimeter tap to verify/monitor
+current during initial device calibration.
+
+If attached battery is really empty, significant voltage drop can
+occur in LM317. Heatsink is needed to dissipate that power.
+
+[[file:current%20limiter/current%20limiter,%202.png]]
+
+Note: resistor gets hot too.
+
+* Indicator panel
+:PROPERTIES:
+:ID: c9a69490-f920-4a31-b32e-b101bfc3d01b
+:END:
+
+[[file:indicator%20panel/indicator%20panel,%201.png]]
+
+Basically 2 digital DC voltmeters and main on/off switch.
+
+[[file:indicator%20panel/indicator%20panel,%202.png]]
+
+Download:
+
+[[file:indicator%20panel/indicator%20panel.png]]
+
++ [[file:indicator%20panel/indicator%20panel.stl][STL file]]
++ [[file:indicator%20panel/indicator%20panel.FCStd][FreeCAD project]]
+
+* Connector terminal
+:PROPERTIES:
+:ID: e33940bd-652f-4ec0-b53b-1c03e16941c8
+:END:
+
+Schematic:
+[[file:connector%20terminal/schematic.png]]
+
+As seen above, most of the USB connectors are used to deliver dual
+power output and 1-wire data connectivity, except one on the bottom
+right. This is used to attach 12V battery. Some capacitors are thrown
+in as well to stabilize against smaller current spikes.
+
+Electrically schematic is realized using smaller prototype PCBs.
+
+[[file:connector%20terminal/make,%201.png]]
+
projects / physical.git / blobdiff