F1/F2 polyfuses gone

Of course, the best-ever design change that could be made to the Pi is one that would be completely impossible for the Broadcom-tied Foundation to make --- replacement of the Broadcom BCM2835 by a better and more open SoC.

Hmmm, did you put something in your tea ?

-J

Expectation enhancement pills, Do The Right Thing brand.

Thanks for the heads up on the 0-ohm change.  Someone at my hackerspace Pi meetup last night told me he got his Pi from MCM last week, so I asked I could see it... and it was indeed "ohmless":

I'm very interested to see at a future meeting what will happen when we swap his Pi into someone's setup who is having trouble with USB devices that might be power related.  With the USB host port polyfuses gone, I'm wondering if it is still be necessary to recommend using a self-powered hub for a WiFi adapter.  (the GWU625 I've been using lists "Transmit : < 380mA. ; Receive: < 250mA").

I was tempted to replace the fuses by a pair of 0 ohm resistors but I only had 1206 size and didn't like how they landed on the pads,

casually I had some 500mA polyfuses of the same size, so I used those.

After the change I didn't have any problems to have an old Digitus Dongle with the Realtek 8187 chipset working directly from the

one of the R-Pi USB ports, this dongle says on the ConfiguratorDescriptor.MaxPower: 500mA

Ddin't do much to test if there is any packet loss issues with WiFi.

-J

For the polyfuse on the micro usb power input, I see on the eLinux wiki it is 1.1A with a hold current of 700mA.  Does that mean the Pi can only draw 700mA before the polyfuse starts to gain resistance and decrease the 5V input? 

I'm guessing the downside to 0-ohm or bigger 500mA polyfuse is that the USB devices can now draw enough current to make the power input polyfuse react.  I wonder if this would effect the functioning off the rest of the Pi (which I think it using 3.3V and 1.8V rails, right?).  Hookup an external harddisk directly and the Pi reboots?

> Hookup an external harddisk directly and the Pi reboots?

We don't really know what the future plans are for power distribution. Morgaine has advocated that the USB power shouldn't go through F3. Some people have suggested 1 ohm instead of zero, or larger capacitors, in order to prevent voltage sags from hot plugged USB devices. Anyway, this change seems like an improvement, even if it doesn't solve all the power issues.

I can't really say, forgot to mention that I'm actually powering the R-Pi from the P1 header so I'm totally bypassing the main fuse.

-J

I can't remember if there is an specific value required/recommended by the USB 2.0 standard, I've been usnig 150µF and the reference design schematics and eval board for the SMSC LAN9512 show that value as well for each port.

The R-Pi has a single 47µF shared by both ports.

PS. I"m still waiting to see what else is on "Pete's list", this "silent" fix by RPF replacing the polyfuses by a 0 ohm resistor is another engineering oddity and it does not sound professional that they decided to do it (and apparently testing it) because we were doing it, they should have a more reasonable explanation.

-J

ah, good point, I forgot about powering via P1.