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MK808B Android Stick PC + RFD900 Radio

This is a 2nd generation prototype intended to address the physical size and slowness issues of the 1st generation. It is also hoped that power consumption may be similar or lower than on the 1st generation through more integration in the Android stick PC.

It would be really nice if we discovered some spare GPIOs on the 808B that could be used to control the RFD900.

Pros:

  1. Much faster CPU and lots of internal storage for Rhizome
  2. Much smaller size than equivalent components in 1st generation
  3. Android based, so power management is probably pretty good (but remains to be tests)
    1. Rooted ROMs are available, and it is easy to replace ROMs:

Cons:

  1. Wi-Fi probably can't do ad-hoc at the same time as AP mode, so:
    1. no ad-hoc meshing when in close range with another Mesh Extender
    2. no connection by ad-hoc mode phones
  2. It runs Android instead of a bare Linux OS, making life a bit more complicated and development slower.
  3. It might end up using a lot of power, since the 808B isn't intended to be battery powered.

Flashing ROMs on the MK808b

The default flashing tool runs on Windows, which is not convenient for us on Linux/Mac. But it is apparently possible to install ClockworkMod Recovery, and flash ROMs using that:

http://blog.geekbuying.com/index.php/2013/03/22/how-to-upgrade-your-mk808b-to-android-4-2-os-with-cwm-recovery/

The actual Clockwork Recovery installation is as easy as copying the CWM zip to a microSD card, renaming it update.zip and rebooting your MK808b.

There after you can reboot into recovery when needed to flash ROMs from the microSD card. To be confirmed is whether you need to press the reset button to reboot into recovery, whether it boots into recovery by default and other such fine points.

This looks like an interesting ROM for the RK903 based versions of the MK808B, which is what I have. This ROM comes with ftdi and cp210x usb-serial drivers included:

http://www.armtvtech.com/armtvtechforum/viewtopic.php?f=111&t=1402

But Wi-Fi/Bluetooth support uncertain.

Also, it is rumoured the RK903-based version of the MK808B has terrible Wi-Fi performance due to poor ground separation from USB. That would be very annoying.

MK802ii

This is the older generation of the same device. It runs @ 1GHz with an older core, lacks Bluetooth and depending on the version has either 512MB or 1GB RAM. Certainly enough for what we need.

Putting a Debian image on is easy: http://romanrm.ru/en/a10/debian I didn't get that one to work, so instead grabbed lubuntu 12.04 from: https://www.miniand.com/forums/forums/2/topics/1 lubuntu is much bigger than I wanted, but for testing will be fine.

Basically this device will boot from an OS put on a microSD card, making life very easy.

It also comes stock with a rooted Android 4, which if it can be made to see a USB2serial adaptor would be sufficient for our needs. Alternatively, we could even try using the onboard serial port on the device. The complication there is that it is already used for boot/console, so we would need to get a bit creative. Also it lacks hardware flow control.

Nonetheless, we will try the on-board serial port as an easier option than finding the usb serial drivers for the Android installation that comes with the unit.

Onboard Serial Port

Serial port wiring for the MK802ii can be found at:

http://www.rikomagic.co.uk/forum/viewtopic.php?f=6&t=2488

The pads are very tiny.

To connect the serial port to an RFD900 radio:

RFD900 | MK802ii
1 GND  | GND
3 CTS (joined to RTS on pin 11) | Not connected
5 +5V  | Not connected
7 RX   | TX
9 TX   | RX
11 RTS (joined to CTS on pin 3) | Not connected

The serial console defaults to 115200bps.

With a cable like that and the RFD900 set to 115200 serial rate, I was able to watch the serial console on boot. Then my serial port leads broke because the glue holding the serial connector on the MK802ii broke.

Anyway, it looks like it should work (not counting the untested power consumption and Wi-Fi performance).

USB Serial (FTDI or CP210x)

Both of these work with the lubuntu 12.04 distribution out of the box.

To connect the RFD900 to a CP210x, you just need GND, +5V, TX and RX lines – there is no hardware flow control by default on the RFD900 or CP210x, so no need to hook up the extra lines.

With this we were able to talk to the RFD900 easily from our MK802ii.

Radio Modules & Antennae

RFD900 radios are AUD$62 wholesale (orders above 20 or so units).

Of the antenna options that rfdesign stock, the dipoles have much better performance due to ground-independence (less local noise induced on the receiver) and reduced transmission losses through reflection. The flexible PCB dipoles (http://store.rfdesign.com.au/rfdflex1-900mhz-flexible-pcb-antenna-no-cable/) are probably the best. These are $7.95 each, plus coax cable and connectors, cost to be determined.

A coax cable solution is probably to buy one of these cables (http://store.rfdesign.com.au/rf-cable-sma-m-srflex-sma-m-30cm/), and chop it in approximate halves. That is a cost of $6.45.

That makes total radio cost $62 + $7.95 + $7.95 + $6.45 = about AUD$85 in quantity.

content/meshextender/prototyping_on_mk808.1366369947.txt.gz · Last modified: 19/04/2013 04:12 by Paul Gardner-Stephen