First, become familiar with the hardware components and the reasons they are used.

3M sticky mounting tape
It is not the revolutions in SBCs, touchscreen or battery technology that made this project possible. Instead, long lasting, heavy duty tape has become widely available that holds most components together.

Kapton tape
If it is good enough for the most reliable machines ever built (Voyager 1 and 2) it is good enough for this project. The exterior shell can consist entirely of Kapton tape if it is preferred not to build one. Experimentation has shown that Kapton traps much less heat than electrical tape. See the shell development page if you want a more conventional covering.

Weboost Home 4G
This cellular signal amplifier is essential to receiving a reliable GSM data signal, which does not penetrate structures well. Typical smartphones do not have the kind of absolute reliance on data as these devices do so a weak connection is unacceptable. Testing has shown that this device makes the difference between a nearly unusable SIP call and a nearly perfect one. Signal strength testing does not show the full picture of the capabilities of this device. The real advantage is in improved data packet loss. Vertical and horizontal separation of the antennas is recommended.

Tiny USB microphone
This is a good performing, inexpensive, compact, convenient, extremely low power microphone. By simply plugging this in and building your device such that this is on the bottom it works well for voice calls and may even have enough sensitivity for "speakerphone" use.

Waveshare 5" 800x480 HDMI screen (H)
TN design
USB input
capacitive screen
on screen button controls with brightness and on/off
hardware scaler
amplifier/headphone port for HDMI audio
displayport/VGA input - not used

Waveshare 5" 960x544 HDMI screen
OLED design
USB input
capacitive screen
no button controls but good defaults
no hardware scaler
no amplifier but has a headphone port for HDMI audio
no displayport/VGA input

Waveshare 4.3" 800x480 HDMI screen
IPS design
USB input
capacitive screen
on screen button controls with brightness and on/off
hardware scaler
speaker amplifier/headphone port for HDMI audio
displayport/VGA input - not used

Philmore (18AWG) DC Extension Cable Cord
this can be chopped up to be used in 2 ways
one side can be used for the device side connector
the other side used for the charger side connector

Icstation 1W oval shaped laptop speaker
loud enough to be heard across a room
leads should be melted with a soldering iron to expose the copper

Adafruit 1092 on/off switch
little voltage drop
very compact

Makerfocus mini voltmeter
uses very small amount of power and is intended to stay running while sleeping
bright enough to light a keyhole

Iuniker USB-C power switch for Raspberry Pi 4
this can be chopped up for use in various ways
the male side used for a charger plug on the charger side or a sbc power plug
the female side can be used for a charger plug on the device side

VSVABEFV 4G LTE cellular device
CDC ethernet type device
built in wifi hotspot for 10 users
high speed with multiple us bands

ZTE MF861 (ATT Velocity) cellular device
CDC ethernet type device
4G LTE
ATT branded and recommended
data sim cards only
folding USB connector
external antenna ports

Tongxiang 4 pin JST PH male connectors with wiring leads
for Lattepanda power wiring
for screen speaker wiring

Kework USB splitter (hub) left or right angle
this is a very small 2 port passive USB 2.0 hub
can be taken apart and housing removed to become even smaller

Cable Matters right (left?) angle micro USB 6 inch
the size of the wiring inside is a medium level of thickness
for screen power
straight at type a and right angle at micro usb

Mxtechnic left (right?) angle micro USB 6 inch
the size of the wiring inside is a heavy level of thickness
for screen power
right angle at type a and micro usb

Monoprice ultra slim HDMI
fpv HDMI cables are even smaller but are fragile and not really needed anymore
these are smaller and more flexible than the typical HDMI connector however

Chargers:

Take care using any charger this way because by default they lack a temperature sensor connection to the battery which is an important extra safety feature. In a typical usage scenario of 1.3A max draw on the batteries, setting the charger to 1.8a will charge the batteries up while continuing to power the device. You should only set the charger to charge slowly on "top" of the power needed to run the device. Charging Lithium ion batteries too fast is dangerous. This may not charge the batteries in an optimal way but avoids a tremendous amount of extra charger design work. A charger/power supply must be used that will be safe to use by implementing auto switching between CC and CV modes, also known as current and voltage limiting.

Tenergy TB6B (charger)
+fanless
-clumsy external power supply
-one digit decimal readout with backlit lcd (1990s)
-terminates charge when it thinks battery is charged
-no pb trickle charge mode
-no pb desulfation
-slow to interact with
-5A

Haitronic HPS305D (power supply)
+efficient power usage
+two digit decimal readout with basic lcd (1980s)
-dangerous and unreliable analog controls
-no way to switch output on and off
-no memory settings
-5A
Initial calibration steps:
turn on
turn coarse amps one quarter turn until mode changes
set coarse volts to desired setting - exactly 4.2V
turn off
short out terminals
turn on
set coarse amps to desired setting - about 1.5A
set fine amps to desired setting - about 1.5A
turn off
un short out terminals
connect load
turn on
set fine volts to desired setting - exactly 4.2V
Post calibration charge steps:
connect load
turn on

HTRC HT100 (charger)
+10A
+pb trickle charge mode
+two digit decimal readout with color touch lcd (2010s)
*unused for lion charging
-slow to interact with

Korad KA3005P (power supply)
+lock mode
+multiple memory settings
+three digit decimal readout with basic lcd (1980s)
+digital controls with hybrid style jog dial
-linear supply with high power usage
-5A

Tekpower TP3010HB (power supply/charger)
+10A
+two digit decimal readout with large backlit lcd (2000s)

Failed/unavailable power supplies:

Drok mini "small" power board
fitment
difficult soldering/only a simple battery indicator
fatal flaw: poor power output - brownout indicator always

Geri Dual USB "medium" power board
fitment/enough power/multistage battery indicator/secondary charge/no rundown bug
requires soldering/fairly large/requires right angle usb
has killed 2 pis under mysterious circumstances
one at startup and one when starting a charge
in addition it is difficult to solder correctly
fatal flaw: random voltage fluctuations - dangerous

Smakn Dual USB LCD "large" power board
fitment/enough power/secondary charge
inaccurate lcd battery indicator/rundown bug/fairly large
fatal flaw: random failures

Adafruit powerboost power board
fitment/small/good power output/secondary charge
difficult soldering/basic battery indicator/no switching/poor output/charge instability
fatal flaw: poor output causes instability

Geri dual USB with LCD display "large" power board https://www.amazon.com/gp/product/B00VDP94QM/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1
fatal flaw: 2 shutdowns within days, failures with similar design, 2 boards at once exhibiting brownouts

Drok "large 2" power board
https://www.amazon.com/Digital-Converter-Adjustable-Regulator-Transformer/dp/B00J03PBW0/ref=cm_cr_arp_d_product_top?ie=UTF8
fitment/enough power/led battery indicator
fairly large/no low voltage protection
Voltage adjustment can be inaccurate but it is easy to connect with screw terminals, should have enough power and has a built in voltmeter.
fatal flaw: sporadic large drops in voltage

Recommended power supplies:

Yeeco DC to DC boost converter "small" power board https://www.amazon.com/gp/product/B010NEG6GE/ref=oh_aui_detailpage_o05_s01?ie=UTF8&psc=1
fatal flaw: Fails with voltage drops at large loads after heating up. Only really good for 1 amp over time.
Recommended anyway as it can be easily put in parallel with an identical supply.

Yeeco ultra-small 3A high efficiency "medium" power board
(no longer commonly available)
Reliable. No power switch. The king of all power supplies. Onboard charging works at 500ma by default but appears to have an option for 1000ma. Onboard charging never interrupts the output. 2 LED indicators with low voltage warning.

Onboard charging and alternate untested power boards:

Drok 3A power supply
https://www.amazon.com/Converter-DROK-Voltage-Regulator-Transformer/dp/B00C92Y1G6/ref=sr_1_19_sspa?keywords=3a+5v+step+up+-adjustable&qid=1550868132&s=gateway&sr=8-19-spons&psc=1

Retired components:

Waveshare 5" 800x480 HDMI screen (A)
The hardware core of the project. Several designs are based on it. It also serves as the "frame" of the device as the component all others are mounted to. The HDMI "jumper" device allows a simple, sturdy, and compact connection that physically locates one side of the screen to the PI and is the key that keeps the entire device together. Any higher resolution would be frustrating to use. In addition the HDMI approach is much less fragile than a ribbbon cable.

Waveshare 5" 800x480 HDMI screen (B)
This uses USB input instead of SPI like screen A. Can use FPV HDMI cable for a flat connection on both sides. Acts as a generic mouse so is optimal for alternative OS and SBC. Does not work with evdev third button emulation.

Waveshare 7" 1024x600 HDMI screen
The hardware core of Model 4. It also serves as the "frame" of the device as the component all others are mounted to. A "borrowed" HDMI jumper from a broken 5" screen combined with a 90 degree HDMI adapter allows a direct connection from screen to PI with no wires.

Huawei E303 USB cellular adapter
This 3.5G device has a thin profile and can be carefully slimmed with a dremel tool even further. May use less power than 308U.

Sierra Wireless 308U USB cellular adapter
This 3G device has small profile similar to the E303 with two indicator lights. Has support for a single external antenna. May use more power than E303.

Drok micro 3w amplifier
This analog board is stereo but only one channel is used for this project. Proper stereo sound requires more spatial separation than a smartphone sized device allows anyway. At full volume is as loud as a midrange smartphone speaker. The board itself is also very small for the available power. It can also directly run off of 3.7v battery power without using up a USB port. The defining feature however is the entirely solderless design. Testing has shown it is not capable of bridging left and right audio channels into a single more powerful mono channel.

Adafruit MAX98357 digital i2s amplifier
Has proven to be a very reliable and clear amplifier. No ground loop issues like an analog amplifier can have. Inexpensive. Adjustable gain pin.

Logitech c525 camera
less trouble then csi
camera/microphone will pick up facing front or rear
will be failure prone when pocketed/bulky
testing - with repeated tests it always works

Adafruit ads1015 adc
reliable
significant wiring/power boards and charger contain a monitoring feature
testing - with repeated tests it always works

Arducam spy camera
small
3 failures-required reseating of both connectors/required rma/reseating required
testing - impractical to use because of failures - alternate csi camera needed

Flashlight module
reliable
significant wiring/large power board contains a flashlight feature
testing - with repeated tests it always works

Notification light
reliable
no negatives
testing - with repeated tests it always works

Uxcell mini snap rocker switch
This switch is thin and rectangular and can fit easily within a device shell. It previously was sold with presoldered leads but now only the switch itself can be found.

Tanbin 4 in 1 micro USB hub
This tiny hub can be used with any USB host with cable modification. The USB connectors can be easily popped off for use in tight situations. Watch for shorts and crossed wires and test the hub with a USB OTG tablet before using.

Sierra Wireless 313U USB cellular adapter
This 4G LTE device has a wide and thin profile with two indicator lights. Has support for 2 external antennas. More care must be taken to locate audio components away from it's powerful transmitters. May use more power than 340U.

Sierra Wireless 340U USB cellular adapter
This 4G LTE device has a wide and thin profile with a generous sized LCD indicator screen. Has support for 2 external antennas. More care must be taken to locate audio components away from it's powerful transmitters. May use less power than 313U.

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