I would like to announce a project that I have been working on for a long time now. This is a MID or mobile internet device in the same vein, with the same unending promise, as the pocket computers of old. Cellular-connected and running a full desktop operating system, this device can enable you in a way that current hand-held mobile platforms will not.
The era of commercial user-customizable personal computers is coming to an end. This inevitably leads to security risks due to increasing proprietization of software, loss of user choice, and the switching of control from the typical user or administrator to a company with profit-driven or surveillance motives.
Fortunately, single board computers, like the Raspberry Pi and products based on it, are leading the way in allowing the return of the kind of computer liberties we’ve enjoyed in the past. These liberties include the ability to build your own mobile device free from corporate and government interests.
With some free time and support from hobbyist touch-screen manufacturers, it is now possible to assemble a somewhat pocketable device using a single board computer (SBC).
When compared to a typical mobile device, these devices are less attractive, have less battery life, and lack access to Google Play or the App Store. However, they also lack user-hostile software and are fully customizable and have true multitasking capabilities.
Model 16 could be described as powerful and raw. It is faster, easier to build, highly compatible, and has more potential for expansion and modification. It is also thick, heavy, hot, inefficient, and rough around the edges.
Model 17 could be described as sleek and refined. It is smart, thin, cool running, and efficient like a modern mobile device. It is also purpose built with little room in the design for error or elaboration.
Review the necessary prerequisites before moving forward:
- GSM Provider: With the current software arrangement and recommended hardware, only North American GSM cellular providers are supported. Specifically ATT, ATT Prepaid, and T-Mobile.
- Latest Supported Hardware: The project typically only supports a narrow range of devices for resource reasons. The coming pages will go over the required hardware in detail.
- Connectivity (Optional): SIP Account for phone calls, email account with external access, and a XMPP provider for private group communication
If you or your organization meets the system requirements then please choose a direction here:
- Work on building a device for yourself or your organization. This link directs the DIY builder/maker to a series of pages such as diagrams, build notes, component reviews and software images.
- Commission Software Freedom Solutions to build a device for you. Choice of model number and custom options. For instance, Would you like a webcam, a different battery, or a more radical custom option? This link reaches out to the SFS email for a quote.
- Free support. It is important that most issues make their way to the bugtracker and are not kept private. Individuals and organizations can feel free to post here for help of any kind.
- Paid Support. If you or your organization requires timely, specific or private support then please contact Software Freedom Solutions directly. This link contacts SFS via email.
- Work on the code directly for reasons such as improvement or study.
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 you prefer not to build one. Experimentation has shown that Kapton traps much less heat than electrical tape.
- 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 all other components 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 ribbon cable.
- Waveshare 5" 800x480 HDMI screen (B). This uses USB input instead of SPI like screen A. This can use FPV HDMI cable for a flat connection on both sides. Acts as a generic mouse making it optimal for alternative OS and SBC. Does not work with evdev third button emulation.
- Waveshare 5" 800x480 HDMI screen (H):
- USB input
- capacitive screen
- button controls with brightness and on/off
- hardware scaling - not used
- speaker amplifier/headphone port for HDMI audio - not used
- PWM backlight control - not used
- displayport/VGA input - not used
- 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.
- Waveshare 4" 800x480 HDMI screen. The hardware core of Model 6, it also serves as the "frame" of the device as the component all others are mounted to. The screen is IPS and is extremely sharp. Uses a power switch for the display backlight like the other screens.
- 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.
- 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.
- Sierra Wireless 313U USB cellular adapter. This 4G LTE device has a wide and thin profile with two indicator lights. Has support for two 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.
- 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.
- 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 than 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
- 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
- Philmore (18AWG) DC Extension Cable Cord. When this cable is cut in half, one side can be used for the device side connector and the other side used for the charger side connector.
- Icstation 1W oval shaped laptop speaker. This very small speaker can be heard across a room. The leads are so small they should be melted with a soldering iron to expose the copper.
- Uxcell mini snap rocker switch. This switch is thin and rectangular and can fit easily within a device shell. It was previously sold with pre-soldered 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.
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 use 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.
Recommended power supplies
- Yeeco DC to DC boost converter "small" power board (https://amzn.to/2GRlc71).
- 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. Two LED indicators with low voltage warning.
Onboard charging and alternate untested power boards
- Drok 3A power supply (https://amzn.to/2GMpRrH)
For comments, questions, and suggestions, please visit the original thread at https://forum.odroid.com/viewtopic.php?f=116&t=31662.