Embedded Open Modular Architecture/EOMA68/Tablet
The Tablet Motherboard
Popular by decree, but only successfully-sold when the price is stunningly low yet the feature-set rich, tablets are the "must-have" for all ODMs and OEMs who aspire to a chunk of the large apple pie. Key goals for this motherboard are therefore to be small, slim, low BOM and low-risk development. Thanks also to the modular design, the board is sufficiently simple that it may even be possible to do as a 2-layer PCB, thus reducing costs even further.
Connectors and Components
The connectors required are:
- 1x USB2
- PCMCIA Connector "inline" (signals conforming to EOMA/PCMCIA Standard)
- 5V Power
- 1x PCI Express "inline" (supporting USB Wifi, not PCI-e Wifi, such as RT2070 and RT3090)
- 1x Stereo Speakers and Microphone
- 1x RGB/TTL LCD Output (with LED Backlight)
- 2x Battery Connectors
Major components are:
- An STM32F106RB Embedded Controller (same as in the Micro Engineering Board
- A 4-port USB-2 High-speed Hub (e.g. GL850G)
- 12.5Mhz XTAL (for the GL850G)
- Power Management ICs (Buck Converters for 3.8v Lithium to 5.0v; 3.3v LDOs)
- An I2C EEPROM
- An RT2070 or RT3090 USB-compliant MiniPCIe WIFI Module
- An Antennae for the WIFI Module
Diagram of Tablet Motherboard Layout
From this diagram, it can be seen that there is very little involved. Like the Odroid, it's possible to have a product where the connectors and buttons define the size of the PCB more than the ICs and discrete components. In this case, many of the major connectors (such as USB-OTG, HDMI, Micro-SD and Headphones) will already be on the EOMA/PCMCIA-compliant CPU Card, leaving nothing left for the motherboard than to provide USB2 and Power connectors! An alternative revision is also shown which takes a USB 3G Modem, in PCI-e form-factor.
Diagram of Tablet Construction
This diagram shows the physical construction of the tablet's components. Critical to achieving a thin tablet, even when allowing for a 5.5mm height PCMCIA CPU Card, is to use an inline PCMCIA header as well as an inline PCI-e connector. If one is used at all (rather than having the PCMCIA CPU card factory-installed) the PCMCIA assembly is shown being attached directly to the tablet's outer casing, rather than being attached to a PCB. Additionally, two batteries are used (in parallel) rather than one, in order to prove a balanced weight distribution to the device. The larger battery sizes, which could even be up to 6mm thickness, potentially allows for cheaper Lithium Polymer batteries to be used - again, reducing the overall cost of the device.