Wifi MyShield based on Atheros AR9331

Hello Community, I'm starting to create my own shield based on Atheros AR9331 with SPI Flash memory 32Mbit CMOS 3.0 and 256Mb DDR SDRAM, the interface that I've foreseen are 1 Ethernet LAN and 1 WAN, UART (RX via pin B68/TX via PIN A79) without USB.

When I receive the PCB from the factory and I power on the shield for the first time, what happen?

Is there inside the AR9331 already a firmware and bootloader or it is completely empty?

Can I install OpenWRT or before I need to do something?

Are useful the only interface UART and/or Ethernet for to do the install/update etc etc activities?


Yun configuration:

RAM 64 MB DDR2 Flash Memory 16 MB


RAM 32 MB DDR2 Flash Memory 4 MB

The price difference:

Flash Memory:

Winbond W25Q32 32Mb/4MB $0.2 Winbond W25Q128 128Mb/16MB $0.5


Zentel A3S56D40FTP 256Mb/32MB $1.0 Zentel A3S12D40ETP 512Mb/64MB $1.8

Upgrade your configuration by cost $1.1 is good deal.

Since AR9331 hsa USB port build in ( host and device mode ), plus a lot of application could be benefit from USB port. It is wise to have USB port.

Hello sonnyyu, many thanks for your feedback.

I take in account your advice, regarding the USB I would like to connect with 3G module not usb doungle.

After surfing on internet more night I've understand that buy the three components above and create a PCB from scratch is possible to install a bootloader and openwrt via UART serial console and/or Jtag interface.

Other to create a bootstrap action with some pullup and/or pulldown some pins of the AR9331-

Could someone confirm?

I would like to have a breakout that host AR9331 for use it on the breadboard, someone know if exist?


DIY friendly AR9331 module (has firmware/bootloader and openwrt build in) list:




Hi sonnyyu, thanks exactly I would like to create my own like yellow Carambola2 module above.

I'm working on and I've a doubt if UART,JTAG and Eth LAN is useful for install bootloader and openwrt on the my module, consider the AR9331, Flash memory and DDR2 that you've advice above.

Could you help me to clear my doubt?

I experience problem to create route for AR9331 package (dual-row LPCC) in eagle cadsoft, could you advice some trick&tips? I would create a breakout board for using on the breadboard.

Many thank sincerely


Both dragino and carambola-2 are opensource hardwares:



mafer: ... I experience problem to create route for AR9331 package (dual-row LPCC) in eagle cadsoft, could you advice some trick&tips? I would create a breakout board for using on the breadboard. ...

Post dual-row LPCC support at eagle forum?


You need sign NDA with Qualcomm to get support.

sonnyyu: B.T.W.

You need sign NDA with Qualcomm to get support.

And will probably need some sophisticated (and expensive) RF instruments to test and calibrate the radio portion of the circuit.

I would think it would just be a whole lot easier and more practical to just get one of the ready-to-run modules and drop it on your own interface board. It sidesteps all of the critical connections, the RF calibration issues, and the initial bootloader issues.

This is NOT going to be anywhere near the same level of effort as plopping a '328P and a few support parts onto a board and burning the initial bootloader image into it. Duplicating most Arduino boards is trivial compared to what it will take to build a custom version of a Yun.

In my mind, building such a board from scratch only makes sense if you are planning on mass producing these boards where every penny counts and where you will sell enough thousands of them to pay for the non-recurring engineering costs which are bound to be be high (I think you will spend a lot of time getting the design right, getting the software built, and figuring out the start-up sequence to get the board booted.)

hello sonnyyu and ShapeShifter, sure that you are right. Thanks for wise word.

Following your advice, I would ask some question on carambola e dragino.

If I embedded one of these module and on my board is also foreseen a 3G module that work via USB+ and USB- , which is best solution to choice between carambola e dragino?

If I foreseen that my board can stackble onto Arduino Mega 2560, which is board more indicated?

Which is the board that has more features in term of Wifi Router mode? At the end my board must be work like a 3G wifi router and it must have the capability for voice/video streaming coming from 3 or 4 webcam ip, send sensor information, send/receive remotly command.

I'm waiting your feedback

Best Regards //Mafer

I don't have any personal experience with either board. But I would think that everything you are questioning (USB, Mega 2560, router features) would be the same between any of them. They both use the same processor/radio, have the same amount of memory, and both run OpenWRT.

I would think that the Dragino HE or the Carambola-2 would be pretty much interchangeable. The biggest difference I see between them is their size/shape, and they have different types of antenna connectors. The difference between the Dragino HE and Dragino Yun Shield is even less - they are functionally identical, the only difference being that one is a bare module, and the other is the same module already mounted on a shield. Minor differences aside, I guess it comes down to price, availability, and support -- I don't have any experience with those aspects.

A final distinguishing feature, and potentially the most significant, is the software. In the case of the Arduino Yun, Arduino has put in a lot of effort to add the Bridge library that makes it easy to talk between the AR3391 and the Arduino sketch. They have also made some significant customizations to the Linux side to improve ease of use and configuration. Have the other vendors put in a similar amount of effort to provide a customized version of OpenWRT? Or do they just use a generic AR3391 build? (Or do they expect you to use Arduino's version and freeload on their software efforts?)

@mafer, why not get both modules ( even boards ) to test them yourself?

If I were you, I will test at Yun first place.