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Tiny, $13 IoT SBC runs OpenWrt on MediaTek MIPS SoC

Dec 4, 2015 — by Eric Brown 20,748 views

The IoT-focused “LinkIt Smart 7688” SBC from MediaTek Labs and Seeed runs OpenWrt on a WiFi-enabled, MediaTek MT7688AN SoC.

MediaTek Labs and hardware partner Seeed Studio have unveiled a LinkIt Smart 7688 development platform aimed at Internet of Things (IoT) applications and with an aim to “extend the LinkIt family of development platforms to the open-source and web developer communities.” The platform offers a choice of Seeed’s LinkIt Smart 7688 ($12.90) or LinkIt Smart 7688 Duo ($15.90) development boards, both of which run OpenWrt Linux on MediaTek’s 580MHz MediaTek MT7688AN system-on-chip. Like Qualcomm’s popular Atheros AR9331, the MT7688AN has a MIPS architecture and integrates 802.11n WiFi (see farther below).

LinkIt Smart 7688 (left) and Duo
(click image to enlarge)

Both LinkIt Smart 7688 boards include a MT7688AN SoC, 128MB RAM, 32MB flash, and WiFi. The Duo adds an Atmel ATmega32U4 MPU for Arduino compatibility. The platform is designed for advanced WiFi-based devices such as IP cameras, surveillance devices, smart appliances, and WiFi gateways that make use of cloud services, says MediaTek.

Reverse view of LinkIt Smart 7688 (left) and Duo
(click image to enlarge)

The COM-like SBCs are each equipped with a microSD slot, a micro-USB host port, and a micro-USB port for 5V power input. On the Duo, this second micro-USB port can also handle data signals.

Detail views of LinkIt Smart 7688 (left) and Duo
(click images to enlarge)

There’s also a pin-out for GPIO, I2C, SPI, UART, PWM, and Fast Ethernet interfaces. The standard Linux-based model, which measures 56 x 26mm, also offers I2S for audio. The MCU-based, 61 x 26mm Duo model instead adds ADC and SPIS.

Reverse detail view of LinkIt Smart 7688
(click image to enlarge)

Taiwanese chipmaker MediaTek announced the formation of its Silicon Valley based MediaTek Labs development portal in Sep. 2014 along with its first two offerings: a MediaTek SDK for Android designed for typical ARM Cortex-A MediaTek ARM SoCs, as well as a LinkIt RTOS that runs on an MPU-like, ARMv7-based, Aster (MT2502) SoC. In October of this year, MediaTek joined with Seeed to announce “MediaTek Linkit One and Grove,” one of 10 Starter Kits for Amazon’s AWS IoT platform. Enhanced with Grove sensors, the kit runs the LinkIt RTOS on the Aster SoC built into the LinkIt One. Linux-based AWS kits include products built around the BeagleBone Green, DragonBoard 410c, and Intel Edison.

LinkIt Smart 7688 breakout (far left), and Duo options (left to right): Arduino and Grove breakouts and Grove Starter Kit
(click image to enlarge)

Seeed offers an optional breakout board for the standard LinkIt Smart 7688, and provides three options for the Duo. The latter include an Arduino breakout, a Grove accessory breakout, and a Grove Starter Kit with a variety of sensors and I/O modules.


Smart WiFi Audio

There’s also a Smart WiFi Audio demo project, which lets your smartphone tap into the LinkIt Smart over WiFi and play music. “If you connect the Linklt Smart 7688 to your Router, the Audio [Smart WiFi Audio Demo] will show the IP on the Grove RGB Backlight LCD, and also the music names,” says Seeed.

Developers can use the OpenWrt SDK to create native C applications for the target IoT device, taking advantage of over 2000 software packages, says MediaTek Labs. Web and mobile app developers can use Node.js and Python. As noted, the Duo versions can also be programmed with the Arduino IDE for real-time control of peripherals.

LinkIt Smart 7688 with microSD connected (left) and Duo with populated pins
(click images to enlarge)

LinkIt Smart 7688 developers can also take advantage of the MediaTek Cloud Sandbox platform for IoT data collection, visualization, and analytics. The boards ship with open specs, including schematic layouts, and pin details. A fully open source version of the WiFi driver should be available in the coming months, says MediaTek Labs.

MediaTek MT7688

MediaTek announced the Linux-ready MT7688 SoC in June 2014 along with a lower-end, RTOS-only MT7681 SoC. Like the Atheros AR9331, the home automation focused MT7688 has a tiny 12 x 12mm package, offers built-in WiFi (2.4GHz “1T1R” 802.11n), and a MIPS24 core. In this case, it’s a MIPS 24KEc design clocked to 580MHz instead of the AR9331’s 400MHz.

MT7688 block diagrams for IoT Device Mode (left) and IoT Gateway Mode
(click images to enlarge)

Although it’s loaded only with 128MB of RAM on the LinkIt Smart 7688 boards, the MT7688 supports twice that amount. The SoC is further equipped with an AES128/256 encryption chip, 64KB I-Cache, 32KB D-Cache, and either a 5p FE switch or a 10/100 Ethernet PHY.

The LinkIt Smart 7688 model uses the MT7688AN, model, which is differentiated from the similar MT7688KN model with its additional support for SD-XC memory, as well as its support for DDR2 memory, in addition to DDR1. The KN model is also slightly smaller at 10 x 10mm.

The SoCs include SPI flash, supporting 3B (max. 128Mbit) and 4B address modes (max. 512Mbit), says MediaTek. Both MT7688 models have 8MB DRAM, which stores eCos turnkey for compact router, repeater, IoT bridge, storage, and audio applications. In addition to these gateway operations, the MT7688AN can also operate it in IoT device mode, which supports more peripherals, like eMMC, SD-XC, SPI slave, 3x UARTs, PWM, and more GPIOs.

Video overview of LinkIt Smart 7688

Further information

The MediaTek LinkIt Smart 7688 and 7688 Duo development boards are available globally from Seeed Studio for $12.90 or $15.90 (Duo). More information may be found at the MediaTek Labs LinkIt Smart 7688 product page, as well as Seeed’s LinkIt Smart 7688 and LinkIt Smart 7688 Duo shopping pages. The voluminous documentation also includes this Seeed LinkIt Smart 7688 wiki page.


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