Evaluating low cost USB to Ethernet converters

Image

A13-OLinuXino have no wired Ethernet connection and using WIFI is not always possible so we were looking around for suitable USB to Ethernet converter which to offer.

There are tons of these convertos on ebay starting from as low as $3 including shipment!

The competition between the Chinese factories is enormous, so you can find generally thousands of variations of every product and have to be little cautious as the general Chinese business model is somehow like this: Company A release product on the market and charge let’s say 100 for it, once the product is well accepted and sales are good company B,C and D immediately are seeing business opportunity and copy the product but try to make it at lower cost, usually this comes not from some kind of innovation but just from using lower grade components or removing some components which are for the FCC/CE safety approvals and release product which looks same but sells for 70.
After a while companies E,F,G decide to enter also this market and make new iterration but now the product cost 50 and as you guess right they use even lower grade components.

On first sight all products look same, but when you got them you see that they do not function equally.
Usually there are brands in China which prduce better products and local knows them, so I asked our sourcing agent to take 4 USB to Ethernet adapters which are from brands he trust.

We got them and needless to say they were looking all the same 🙂

Imageso we start our tests:

#1 was not recognized when plugged for a first time, maybe bad USB connector? then after few plugs and unplugs it start working, we copy 60MB tar file and measure 800KB/s transfer which is not bad, opening this dongle and looking at the components it uses AX88772 USB to Ethernet converter which supports 480Mbit mode

#2 was recognized and enumerated correctly from the very first time it works 5 times slower compared to #1 and we achieved only 150KB/s, opening and looking at the components show QF9700 USB to Ethernet converter which supports USB 1.1 only 12Mbit mode (although on the package is written USB 2.0 😉 )

#3 was not recognized at the first time and after a while started working but we didn’t manage to copy file with it, probably lot of packets were lost from time to time this adapter was managing to open web site, but overall it was worst than all we evaluated, inside was QF9700

#4 worked from the first time and achieved 800KB/s same as #1 inside is AX88772 and this definitely is the best perfrming adapter of all 4 so probably this is what we are going to stock and offer as A13-USB-Ethernet adapter

out of couriousity we try LAN9512 which we put on iMX233 and the transfer was similar to AX88772 i.e. about 1MB/s.

Low Cost LCD-TO-VGA adapter

Image

A13 processor have no HDMI and VGA output as his big brother A10, so we had to work out something using the LCD interface it have.

We browsed IC video DACs and there is plenty of them, but they are expensive and didn’t fit well OLinuXino low cost concept, so we decided to give a try and make simple R ladder video DAC.

A13 LCD interface is 18 bit this means we will need 3 channels x 6 bit Video DAC.

All VGA monitors have 75 ohm terminator on their input lines and the video signal is 0.75V for white level and 0V for black. So knowing this we could make resistor ladder DAC with R, 2R, 4R, 8R, 16R, 32R connected in parallel with RGB 0-5 bits. The values are easy to calculate when we know the LCD buffer output voltage 3.3V and the voltage we want to have when all bits are “1” i.e. 0.75V. The resistors using the 1% precission values picked were 549 ohm, 1050 ohm, 2180 ohm, 4370 ohm, 8660 ohm, 17800 ohm.

The adapter was routed and pcb prototypes were run. The assembled adapter was attached to LPC1788 board with 4.3″LCD with tweaking the output to match VGA lock frequency and the result was perfect.

Image

The picture which appears on LCD was color stripes with small ball which you can move by tilting the board (using on-board accelerometer), as you can see from the picture the colors are perfect and image is standing still with no glitches and jitters.

So now we have low cost VGA solution for our A13-OLinuXino and can move forward with the PCB schematic finish and routing. Note that the VGA signals go through buffers which are gated i.e. we can enable and disable the VGA output and A13-OLinuXino will be able to work with both LCDs and VGA.

EDIT: schematic is included here below:

Next Newer Entries