Necromancer's notes

Just received this thingie. I was attracted by the price, avaliability of kernel sources and the fact I really needed an embedded PC for my needs. Once I got it, the dongle with usb and ethernet caught my attention so I disassembled it. And… what do I see?

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I got quite a bunch of these thingies some time ago, so it was just the time to get the fun started. At least I needed a car charger for my tablet badly. The wall plug is said to provide 9 volts up to 2,5 Amps. So GS6300 3 Amp thing was just what I needed.
The datasheet for the chip sucked: really little detail and only one application circuit. Luckily, the application circuit was quite simple to understand, so with minor modifications I made a small power adaptor for my flytouch II tablet.

Hints: Make sure you use the right core for the inductance: if you pick the wrong core, you’ll get GS6300 to heat up pretty fast at some 500-600mA consumption.
If you get the diode with the wrong trr (reverse recovery time), you’ll get it to overheat and won’t get enough current.
At first I used a 10k POT to adjust the output voltage and got it to be VERY unstable. 1k POT solved the problem.
Tab is connected to the GND pin, so make sure you have some nice’n’big ground polygons do dissipate all the heat, unless you want to attach a heatsink. At big currents it heats up. (a charging tablet + max brightness screen + a 3g modem plugged into the tablet).
There is the photo of the assembled thingie:

Since I didn’t have the car’s smoke’o’plug around, I wired the raw voltage from a 5v dc-dc stepdown I had around.

Well, It relly rocks when you have an access to a laser cutter and have some spare acrylic. Some time ago I’ve done this test-tube holder I use in my lab.

Instead of the actual test-tubes I use bottles from ‘bifidum bacterinum’ I used to take whenever I got my stomach screwed by antibiotics. Therefore, I have a sh*tload of ’em. So there goes a photo of the thing:

The source code for the OpenSCAD project is below, licensed under the beer-ware license.

rows=2;
cols=5;
spacing=2;
borderspace_w = 4;
borderspace_l   =  20;
radius=8.5;
drill_via=1.6;
delta=0.1;

TARGET=2;
//////////////////////////

length  =  borderspace_l*2 +  spacing + (radius*2+spacing) * cols;
width   =  borderspace_w*2 + spacing + (radius*2+spacing) * rows;

module vials(rows,cols,spacing,radius, borderspace_l, borderspace_w, shift)
{
length  =  borderspace_l*2 +  spacing + (radius*2+spacing) * cols;
width   =  borderspace_w*2 + spacing + (radius*2+spacing) * rows;
echo("Vial holder: length: ",length, "width:", width);
difference(){
	for (j=[0:rows-1])
	{

	for (i=[0:cols-1+ ( j % 2)])
		{
		#translate(
			[
			borderspace_w +radius+spacing + (radius*2+spacing)*j,
			-shift * (j %2 )  + borderspace_l  +radius+spacing + (radius*2+spacing)*i
			]
			) circle(radius);

		}
	}
}
}

difference()
{
	square([width,length]);
	# translate ([width/4,borderspace_l/3])circle(drill_via);
	# translate ([3*width/4,borderspace_l/3])circle(drill_via);
	# translate ([width/4,length-borderspace_l/3])circle(drill_via);
	# translate ([3*width/4,length-borderspace_l/3])circle(drill_via);

	# translate ([2*width/20,length/2-radius-spacing/2])circle(drill_via);
	# translate ([2*width/20,length/2+radius+spacing/2])circle(drill_via);
	# translate ([18*width/20,length/2])circle(drill_via);
}

if ( TARGET==1 )
{
	translate([width+delta,0]) difference(){
	square([width,length]);
	# vials(rows,cols,spacing,radius, borderspace_l, borderspace_w, radius);
	# translate ([width/4,borderspace_l/3])circle(drill_via);
	# translate ([3*width/4,borderspace_l/3])circle(drill_via);
	# translate ([width/4,length-borderspace_l/3])circle(drill_via);
	# translate ([3*width/4,length-borderspace_l/3])circle(drill_via);

	# translate ([2*width/20,length/2-radius-spacing/2])circle(drill_via);
	# translate ([2*width/20,length/2+radius+spacing/2])circle(drill_via);
	# translate ([18*width/20,length/2])circle(drill_via);

	}
}
else
{
	translate([0,0,15]) difference(){
	square([width,length]);
	# vials(rows,cols,spacing,radius, borderspace_l, borderspace_w, radius);
	# translate ([width/4,borderspace_l/3])circle(drill_via);
	# translate ([3*width/4,borderspace_l/3])circle(drill_via);
	# translate ([width/4,length-borderspace_l/3])circle(drill_via);

	# translate ([2*width/20,length/2-radius-spacing/2])circle(drill_via);
	# translate ([2*width/20,length/2+radius+spacing/2])circle(drill_via);
	# translate ([18*width/20,length/2])circle(drill_via);
}
}

The good thing of my little Rigol DSO is the USB port, where I can pop the flash and dump data in CSV. However, when you have thrown in some bash/python script to analyze the data, or just want do download the pics, you have to remove the usb flash. In the first case, you get bored popping flash in and out pretty soon.
At least I am, sine I’m a still a lazy programmer.
So, what’s the deal?
I took a look at the junk around, and found a nice switch. The I etched a small PCB, and fixed the whole thing to the shelf. I will still have to cover the pcb with urethane, though. Pics follow:



Basically, it’s dumb. Really dumb. You connect the flash to the slot, you connect one cord to your rigol, the other one to some PC. It just switches the 2 data lines from one device to another. So, when I want to connect it to my tablet, instead of rigol… I just flip the switch. Later, after some testing I added 30k pulldown resistors on the data lines, to eliminate some false device detections, when the device is switched off, or not present. (Conductive flux?)
There’s also a known bug with some devices: since power doesn’t get switched, the usb device doen’t get a cold-reset. And they do not get resetted properly. In my case popping another card reader fixed the issue. Making the switch disable the power for a short time will also allow these broken devices to work.

Kicad project files are here. (Schematics are messy – I was in a hurry)
NB: remember to grab eagle converted libraries for kicad, since they have that nice miniusb jack module I used here.

Ok, not porting, but more like adding support for the board, ’cause the chip is already quite known.
I got this thing from my favourite place to waste money – DX. It has RTL3050F inside, 32MB RAM, 4MB FLASH, and runs at 320Mhz. A good bonus is a usb host and a usual uart, well hidden in a small case.
Obligatory photo follows:

Ok, so what next? As usual, the first thing I do, once I get a router… Turn on the soldering iron, take it apart and solder the 2,54 header to connect to the uart. Hehe.
UART is here, the usual 4 pins. GND, RX, TX and Vcc. Logic levels are 3,3 volts (As if I expected anything else), so I just soldered the pins and hooked the bus pirate.

The board is shipped with u-boot, has no jtag whatsoever (careful not to brick – or else you’ll have some bad time desoldering the flash chip, programming it and soldering back!).
Next I got the latest OpenWRT trunk… To just find that this thing doesn’t boot with any of the images generated.
the MOFI3500-3GN image kind of worked, but complained about incorrect mtd patitioning schema.
Time to get some coffee and start hacking OpenWRT to get things right.

As the result, I:

• Created a new mach-type called ‘mach-unbranded-3gn’
• Altered the scripts to correctly pack the firmware for this new supported router.
• Figured out the correct GPIOS for LEDs, so that all 5+1 leds that can be controlled are avaliable from /sys/class/leds
• Figured out the GPIOS for both buttons at the back to work
• Altered some scripts to correctly extract firmware for wireless chip
• Sent the patches to openwrt-devel.

Well, I really wanted to make my own version of a locket with leds, as seen on HaD some time ago. So I ordered some lockets as soon as I could.
However, the seller did include a smaller locket as a gift…. And I couldn’t think of a use to it… Well, until I gave it a thought.
Meet the ee-locket! A locket with 64k of eeprom embedded in it on a tiny PCB.

P.S. Still needs some ultrasonic washing…

I work with a lot of different embedded boards. Most of them have linux istalled. And what do these have in common? Yep. UART. The thing you use to debug them, send uboot parameters and etc. When there are a plenty of boards around, you tend to have a pile of usb<-->uart chips around, your /dev/ becomes a mess (Is that ttyUSB0 or ttyUSB1?) that even udev cannot sort out (Damn, I’ve swapped that out, so it’s not /dev/armboard1)…
And the worst is the difference in logic levels. I have a couple of exotic boards that require 2.5 volts. Something few uart bridges can handle out of the box.
So I had a quick look at what I had around. Since I mostly work with one board at a time…
1. I grabbed an ft232rl
2. Some buffers and shift registers
3. Some POTs and ams1117 voltage regulators
4. Lottsa coffee

The idea was simple as hell. MUX the UART and select the channel you want to work with a small command line utility. FT232RL has the CBUS pins that can be used in bitbang mode. e.g. You can use them as GPIO. 4 GPIO are quite enough for 2 shift registers.
Each shift register has clk and data pins, which you can use to serially input the data, and 8 pins of parallel output, which are used to actually cotrol hardware.
So, my FT232RL got 2 shift registers.
One selects the power channel, the other selects the adress of the UART outlet to use.
Forthe power circuit, I had no mosfets around (huge 10 Amps thingies do not count), so I made use of some PNP transistors in digital switch mode. After the switch there goes a linear stabilizer – AMS1117, adjustable version, which is adjusted by a POT. And after that through a Schottky diode (Is it really required?) it goes to VCCIO power net.
So we have 7 power channels. 3.3, 5 volts and 5 adjustable channels. The voltage can be anything fro 2 to 5 volts so that gives us some freedom of choice
The baseboard has 2 pin arrays that will be used to connect arduino-like shields with buffers and outputs. One has the address selection shift register outputs, that will be connected to ‘/inhibit’ pins of the buffers on the shields, one has the actual outputs of FT232RL serial port.
So I set off to work and after one wasted day of my life I got a baseboard ready. There it is, my little thingie:

.
There were a few bugs though. I had a wrong kicad footprint that resulted in the need of turning all the sot-23 transistors over. And the Schottkey diodes were a bit smaller, so I had to bend the contacts a bit. I also made a small mistake: Since the shift registers are powered via the VCCIO voltage, disabling all power to this net results in inability to supply any voltage again unless you short VCCIO to some voltage and then turn on the correct transistor. So I sacrificed one adjustable channel and made it always output 2 volts of ‘standby’ to the VCCIO net.
Next weekend I’m gonna make some shields and finally publish all the fixed circuits and layouts.
Btw, that’s plain press’n’peel method I used to make the board.