Raspberry Pi - Hardware Flaws and Fixups?

All

As a follow up to my previous post here is an X-Ray of the Micro USB.

Sorry about the funky colour scheme but it hard to pick out the tabs from a lump of solder (lead free) around them (blue in blue).  You should be able to see that the tabs are present and will resist the lateral force applied.  They are not as tall as the thickness of the board as they are primarily used on very thin laminate (0.6mm) and we are at 1.4mm.  I should also mention that we are looking from the back through the PCB.  You can also just see below the tabs, the green area with yellow flecks; that is the two solder pads under the front of the connector, and they seem to be reasonably well soldered.  The voiding (yellow flecks) are normal some better than others.  The orange tubes to the left are vias in the PCB.

I'm sure if we get any failures of this component I'll be the first to know, because you guys will tell me.

I think I'll go an chase some of these posts on power issues relating to duff cables and 'suspected' duff polyfuse parts.  Let you know what I find.

Pete

Thanks for the microUSB x-ray, very informative! Will look forward to more updates. And meanwhile, this is a cautionary tale:

http://www.raspberrypi.org/forum/general-discussion/close-call-nearly-bricked-my-rpi#p66238

Hi Pete,

If you're interested, I would think that people who are having troubles are using a power cable or power supply that isn't good enough.

You must be aware that I and others have measured cables at 3-5 Ohms. That is surely not going to work out well.

I haven't measured the average current yet, but it could very well be about 0.3A. With a 1 Ohm cable and a 5.1V powersupply that would lead to the 4.8V that someone measured with a multimeter.

However a burst of 0.7A will then deplete the 220uF in under half a millisecond. (I'm assuming a 0.7V dropout for the 3.3V regulator). That's way too fast to measure with a multimeter. And it's way long enough to brown-out the CPU and/or LAN chip.

Roger & All

I'm seeing a few issues relating to this 'brownout' problem.  I've got someone looking at this with fast scope and a selection of cables / PSU's to try to bottom this.  We have not seen this problem in our test set but that is the joy of putting something in the field.

I'm also trying to get a handle on the population of users that have a problem with this.  Interestingly in one of the tests we did is to run the board w/o the 220uF present and it still worked without problems - so you could be onto something.

Thanks for the input.

Pete

Roger you wrote: "However next in line is my I2C interface. This too is labeled on the GPIO port as: I2C SDA, I2C SCL, and I'll have to guess which of the several I2C interfaces is connected to the GPIO pins"

The wiki says the I2C are SDA0 SCL0 !

Are planning on doing an I2C driver?

I have a batch of Real Time Clock modules that I'd to love to start selling but would like to get them tested on an R-Pi first!

Or is anyone else with an R-Pi /getting in the next batch, interested in writing an I2C driver? If yes please email me: chris@cjemicros.co.uk

I'm told that the Linux sources have a driver for the DS1338 that I've used! (there is also support in the RISC OS sources which is how we have tested our design)

Hi Chris,

I've gotten I2C working now from the commandline "bitibanging" utility. I was just browsing around on the forum to find a place where I can post a link to the software. :-)

Which reminds me: I don't have I2C read implemented yet....[time passes] .... OK. Done! :-)

Here are the commandline utilities to control GPIO, SPI and I2C.

http://www.bitwizard.nl/software/gpio_spi_i2c_20120419.tgz

Some sample scripts are included to make it easy to work with my I2c and SPI boards.

I'll start looking into writing the I2C and SPI kernel drivers shortly.

It could very well be that I decide that what I want from a kernel driver is not what the standard I2C and SPI kernel drivers do. I want to be able to easily, from userspace, interact with the devices on the bus. Eventually it should be something like:

echo 1 > /dev/motor

and the motor starts turning. :-)

OT: Chris, your name sounds familiar. Were you involved with Linux in the early years? Google shows that there is an actor with your name too. (or is that you?) :-)

Great work Roger! I've emailed you via the bitwizard site.

There are a few Chris Evans's about. I'm new to Linux!

Ha, I already wondered how long it would take you, to show something like this....

I think it is a good picture for the frontpage on raspberrypi.org....

Can you perhaps measure the pcb for me. I am getting different answers from people.

Best guess now is  85.0 x 56.0   or  85.0 x 56.2

Hans

Observation about USB power supplies: not sure if relevant to RasPi or not.

I was making some load measurements on a bunch of 5V USB power supplies here, unrelated to RasPi stuff. Got some confusing results, until I realized something I didn't know: some of those cable-less "wall wart" USB power supplies with just a USB jack, connect the internal ground pin (cable black wire) to the connector shield (cable braid), and some do not. So in some cases you'll have the ground return current flowing on the shield (if your device connects ground and shield) and in some cases, not. In case of interest.

Thanks for all the info Pete. A summary of possible 'minor' hardware changes that I've spotted in the forums:

1. I2S implement  as per the data sheet

2. SD card voltage option bank change, as per Dom's posting in: http://www.raspberrypi.org/forum/general-discussion/where-is-the-bottleneck#p62401

3. USB OTG Id Pin to spare GPIO pin (effective only on Model A) as per:

http://www.raspberrypi.org/forum/features-and-requests/cheap-but-crucial-model-a-feature-request-read-this?value=gpio%20usb%20pin%20request&type=2&include=1&search=1&ret=all

I'm not sure if the next two are technically possible!

4. Assisting POE (spare wires variant) adaptors exist that inject power onto the unused lines of ethernet and then split them out again after a cable

run see: http://www.cjemicros.co.uk/micros/individual/newprodpages/prodinfo.php?prodcode=4D-RPI-POE-IS-C (The Raspberry Pi adaptor cables doubles the price!) but if R-Pi's RJ45 could be changed for a variant that took the extra lines Earth to R-Pi's Earth and the Injected Power lines to R-Pi 5V via a link.

Pros: simple for end users to setup and injector only cable should be cheap.

Cons: POE variant of RJ45 with magnetics needed [1], cost, Reduced Isolation and extra link needed.

5. Assisting POE (via GPIO daughter board) If a POE daughter board was plugged into the GPIO pins with the daughter board having a POE input

RJ45 on it, supplying power to the R-Pi. The four ethernet data line output from the daughter board being connected to currently unused GPIO pins. I suspect inputting ethernet via the GPIO pins breaks various rules and could add to RF output:-(

Original suggestion at: http://www.raspberrypi.org/forum/features-and-requests/routing-ethernet-pins-4578-to-the-expansion-port

[1] I found a mag jack that might the type needed at: http://www.adam-tech.com/catalog/2012/page_009-049.pdf

See page 37 of 41 (marked Page 45) layout M16

n.b. I'm intrigued, what do the two diodes on the underside near the USB sockets protect?

I'd thought the USB ports, but people have mentioned on the forums that they have (unreliably) powered R-Pis via one of the two USB ports.