Assembly Howto - bobbybudnick/SFS-Mobile-Internet-Device GitHub Wiki

Device build instructions

Model 42 Bill of Materials
5" screen
pc stick
cellular device
speaker
speaker connector
fpv hdmi
hdmi coupler
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step down
sacrificial female usb-c charge connector
2s battery
battery switch
device micro usb to type a
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1 passive 2 port hub
switch
screen micro usb to type a

Model 38 Bill of Materials
VIM 3
4.3" screen
Screen factory micro usb with strain reliefs removed
Right angle hub with trimmed device connectors
Slim 6" HDMI
Long thin cellular device with trimmed housing
Custom 2s battery pack with voltmeter/power switch/charge connector/USB-C or VIN
Speaker with connector cable

Model 38
This is one of the more complicated devices to build with the small size
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VIM 3 and screen
Add thick copper heatsinks to VIM 3
Bond VIM 3 and screen such that both rows of buttons are in alignment
Attach stock screen USB with trimmed strain reliefs to VIM 3 and screen touch port
Trimmed cellular device mounts alongside VIM 3 on GPIO side
Attach slim 6" HDMI between screen and VIM 3
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Hub
Must be located between VIM 3 and battery
This is because it must be left angle to clear USB-C
There is only enough cord length for this location
Lengthening the cord or otherwise breaking the EMI integrity is ill advised
Needs housing removed and internals wrapped with kapton tape
Route input wire past CPU and out beside buttons
Trim accessory connector on top and mount against side of batteries
Trim cellular connector all around to clear screen
Attach cellular device to hub cellular connector and pivot inward to save space
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2s battery
Connect positive of battery 1 to negative of battery 2
Connect switch to positive of battery 2
Voltmeter/charge connector/VIN/USB-C between negative of battery 1 and switch
Leave battery slightly above buttons to allow room for protruding hub wire to fold down
Mount voltmeter on bottom of screen and power button on top of screen
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Model 38 alternate improvements
Use USB-C charge connector instead of barrel
Use Cable Matters left angle micro USB instead of stock USB
Mount voltmeter on top of screen flipped on back to save space
(Optional) use side mounted 40x40x10 5v fan attached to GPIO pins

Model 17
screen volume to max
solder secondary power supply to battery wires
solder charge connector to battery wires
solder mini jst connector to battery wires
attach battery to screen with thermal tape
remove rtc connector from board
solder micro usb or pin header to board usb 1
remove micro usb connector from tiny hub
solder tiny hub or pin header to board usb 2
attach mini jst to board battery connector
attach board to battery with thermal tape
attach hub to battery
attach right angle micro usb from board to screen touch
attach power supply to battery
attach right angle type a usb to power supply
attach right angle micro usb from power supply to screen power
solder speaker wires to normal jst connector
attach speaker jst connector to screen innermost pins
attach speaker to screen micro usb cable

Model 16
screen volume to max
ethernet/usb mounting ears cut so board will lie more flat on screen
thermal tape attached to screen
board aligned 2cm from screen bottom left and just off left edge
mini zip ties between board and screen mounting holes
3d printed platform taped above screen buttons for battery
3 x 18650 batteries soldered to power supply and charge connector
3 x 18650 batteries attached to platform
2 x power supply taped to board away from main heatsink
main power cable plugged into power supply and attached to power pins
charge connector zip tied to upper left screen ear
cellular device on top of battery flush with screen edge
screen audio connector trimmed to fit standard jst connector
connect jst connector on inside pins with red inside
jst connector lightly superglued in place
mini speaker soldered to jst connector
switched micro usb to right angle connected to screen and upper usb2
tape screen switch on top of type a connector at top of device
right angle to straight type a connected to microphone/hub and lower usb2
right angle to right angle type a connected to cellular device on usb3
mini speaker taped to screen microusb connector

Model Zero
Tools:
pliers, micro cutting pliers, micro drill bits, soldering gun, zip ties, duct tape, putty knife, silicone, superglue, mounting tape, tweezers Notes:
screen:
use 4 inch SPI screen
shorten header screen edge by 0.5mm and pi edge by 1.0mm
carefully separate touchscreen from board with putty knife
duct tape two parallel zip ties to table edge
attach screen to zip ties with holes hanging over edge
disassemble header top by pulling plastic top
disassemble header bottom by pulling clamps while heating from bottom
fix holes with micro drill bits
solder shortened header on long side to touchscreen
solder pi zero standard with tape supports to combined assembly
protect pins on touchscreen with tape
rebond touchscreen and board with silicone
attach hdmi adapter and trim top flush with E303 and side flush with amplifier
cellular:
use Huawei E303
trim length, sides, side opposite sim as short as possible
remove entire case of cellular device
tape sim card to cellular device
place cellular device wherever possible
audio:
pi zero lacks analog audio but has i2s audio
pi i2s audio lacks digital to analog conversion
must use i2s amplifier
use adafruit MAX98357
use right angle gpio
solder speaker directly to amplifier
must use 5v power for amplifier because 3.3v is quiet and has static
must use a 100k resistor between gain and ground for max volume
volume is still noticeably less than the 3w drok analog micro amplifier
i2s-mmap-overlay.dts must be compiled and added
to compile overlays dtc must be patched
comment out snd_bcm2835 in /etc/modules
add device tree entries for hifiberry-dac and i2s-mmap in config.txt
comment out dtparam entry for audio in config.txt
add custom /etc/asound.conf
place amplifier wherever possible
hub:
use 2 port OTG hub
remove hub case
remove strain reliefs
strip hub input to bare connector
strip port 1 to bare connector
strip port 2 to bare connector or replace with 90 degree female
if using original ports trim underside of hdmi adapter for more space
place port 1 directly on top of hub to save space
place hub wherever possible
power:
use single battery
use Adafruit Powerboost 1000C
does not charge properly thus an external charge connector is needed
can be used for output and is the only board to come without built in connector
directly wire power board to microusb and female dupont
superglue instead of tape for better clearance
place power board wherever possible

Model 6
cellular device situated to expose antenna to outside (SIM inward)
power supply located between pi and screen with power button exposed on top
amplifier located directly beside power supply and above cellular device

Model 1 Basic
Individually charge lithium ion "cells" to 100% with test leads
Optional - break the plastic side opposite the sim card on the e303 for more room
Cut and strip all wires enough to twist together leaving enough length for errors
Twist all positive "cell" leads together
Twist all negative "cell" leads together
Bond lithium polymer (flat) batteries with silicone base heat sink compound
Twist positive power supply lead together with positive leads
Twist negative power supply lead together with negative leads
Twist female barrel plug positive lead together with positive leads
Twist female barrel plug negative lead together with negative leads
Locate amplifier power wire and twist negative together with negative leads
Locate amplifier power wire and twist positive together with positive leads
Solder and electrical tape all positive leads
Solder and electrical tape all negative leads
Locate amplifier signal wire and twist red and white leads together
Twist amplifier signal wires together with 3.5mm cable red and white leads
Twist amplifier signal black wire with raw or black wire in 3.5mm cable
Locate amplifier speaker wire and twist positive with speaker positive
Locate amplifier speaker wire and twist negative with speaker negative
Solder and electrical tape all signal wires
Solder and electrical tape all speaker wires
Attach pi GPIO to touchscreen GPIO
Attach HDMI jumper to pi and touchscreen
Attach USB microphone
Attach right angle type a to right angle micro USB to right side of power supply
Tape both USB ports on power supply and install tightly to touchscreen
Attach right angle micro USB to pi
Turn power supply off by holding button down for a few seconds
Plug in amplifier to speaker
Plug in amplifier to power supply
Tape amplifier to top of power supply leaving room for micro SD
Electrical tape over side of battery pack to face pi
Tape speaker to opposite side of power supply from amplifier
ttach 4 1cm square double tape stacks at 4 corners roughly from pi CPU
Attach battery pack to pi with double stacked tape
Tape cellular device flat against touchscreen and close to power switch
Attach right angle male type a to female type a to pi
Attach right angle male type a to female type a to cellular device
Secure any excess wiring with tape
Optional - connect small LED with resistor to gp21 and gnd

Model 1 Full-featured
build flashlight module with 2 diode/logic level mosfet/led/3 female jumpers
build specialized usb splice assembly for flashlight/ADC/cellular device/amplifier
build usb camera assembly by remove case/shorten cable/replace with right angle
build notification led assembly with led/resistor/2 female jumpers
build amplifier assembly with speaker/integral right angle signal connector
build power assembly with batteries/connector/ADC sensor/board leads
attach power board to screen flush with top edge and power switch
connect main camera/5 gpio pins/touchscreen/hdmi jumper
attach cellular device/attach adc/attach flashlight module/attach led assembly
connect specialized usb splice assembly/bluetooth/adc power/adc gpio/cellular
attach front camera to specialized and bluetooth usb connectors
connect power assembly to adc sensor/amplifier
attach batteries with heatsink cement/attach connector/attach batteries to pi
connect microusb connector and power assembly board leads to power board
attach amplifier upside down and over top power board/speaker opposite mic

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Wiring notes

Direct battery to amplifier wiring
not optimal because amplifier does not get as much power
not optimal because triggers phantom power on bug
not optimal because may cause hardware failure on medium power board
not optimal because causes drain when powered off
*direct to usb is not optimal either because it uses up an entire port
*one approach is to splice into the existing cable for the cellular device
*another approach is to backfeed power from the screen micro USB connector

Audio without the buzz
(problem is a ground loop)
(this is because the pi and amplifier share a power source)
(this means dc power travels across the ac signal lines)
(transformer based isolators avoid this by changing signal ground potential)
(an optoisolator also works and is likely what real smart devices use)
use "smof" brand slimline isolator
take apart isolator casing
use angled usb cable in direction opposite ethernet
plug angled usb cable in bottom left usb port
attach isolator to bottom of angled usb cable attach right angle audio cable to isolator and pi attach amplifier to isolator with right angle audio cable

Flashlight module wide view

Flashlight module closeup view

Flashlight module wiring diagram

Specialized USB wiring diagram

Power assembly wiring diagram

Parallel 3x18650 battery pack
cut 3x6 inch lengths of 18 gauge speaker wire
crimp .187" female spade connectors to speaker wire ends
electrical tape three 18650 batteries together in middle
attach spade connectors to soldering tabs and tighten with pliers
secure connectors flush with battery sides with tape and glue
attach positive leads together
attach negative leads together

USB stability wiring diagram 1

USB stability wiring diagram 2

USB stability wiring diagram 3