Pi accessories from Farnell ... USB chargers?

With cellphone chargers being so iffy on their specs, it might be better to get a USB type A to micro-USB type B lead like this one --- http://uk.farnell.com/pro-signal/hk-us10-1/lead-usb-a-male-micro-b-male-1m/dp/2085464 --- and use a powered hub as the "USB power supply".

A decent amount of power capacity and in-spec USB voltage (yay, voltage regulation!) would then be reasonably guaranteed up to 500mA, and a multi-port powered hub is certain to have headroom above that.

Morgaine.

STOP PRESS.  The last suggestion may not be possible.

The Pi is not USB compliant on its power input, since its micro-USB data lines are not connected.  It won't self identify as a USB device nor will it announce to an upstream hub that it wants more than 100mA, so the whole idea may collapse on its face.  It depends entirely on how the hub will treat this rogue anonymous device that is trying to obtain current illegally.

Morgaine.

Some USB hubs (like my Inland US$5 special from Fry's) don't to anything clever with +5V.  They just connect +5V directly to the USB A connectors for the downstream devices and couldn't care less what the data lines are doing.  So your trick should work fine with my cheap hub provided that my micro USB cable is conductive enough.  My hub's +5V either comes from an external +5V power supply or from the connection to the upstream host through a 1A Schottky diode so hub +5V won't power the upstream host.

A smart hub might protect itself from rogue downstream devices by controlling how much current goes to them and implement nice things like slow start to prevent voltage glitches when you plug in new devices.  I don't have experience with such a hub, or even know if such actually exist.

I like the idea of powering RasPi from a dumb powered hub so I don't have to run current for USB external devices through PTC fuse F3.

I was doing this originally with my Pi.

I found that even with a pretty dumb/cheap powered USB hub, there was still a good amount of voltage drop when measuring the TP1 and TP2 points.  I found that the tracks inside the hub were generally not heavy enough to carry more than 500mA and I was often seeing around 4.7v even though I had a decent 5v 3A PSU supplying the hub.  I eventually opted for creating my own Y cables (to power the hub and Pi from the same PSU) and that seems to give me the best voltage across TP1 and TP2 as I now get around 4.89v using a Y lead with the same PSU. 

YMMV.

The USB current thing is interesting.

Apple devices won't charge from an 'non apple' usb charger, even though other devices will.

Since the chargers don't contain anything the device can talk to, they apply a voltage to the D+ and D- pins, and the apple device then decides how much it can suck.

I suspect that all the usb chargers are the same, unless they incorporate an intelligent usb device, the device will need to know it can suck more.

In the case of the Pi, the micro USB doesn't have any data pins connected, so it will suck as much as it needs from the charger.

I went through 5 different chargers that had a USB socket, all capable of 1A or more, and they all failed to provide enough volts.

The cord drop was measured and sure different cords varied slightly.

Even a genuine charger for a smartphone with a micro usb plug didn't provide enough.

I suspect that most phone batteies now are 3.6v, so it doesn't really matter if its 5v or not.

In the end I used a 1A charger made by Brightlink and distributed by Brightpoint.com thru The Warehouse (here in NZ and AUS)

Mark

So far have tried a generic one that I had already- not too much use,

Ordered (and in the process of returning) one from Amazon which was sold as a 5V 2A charger..... nice, however, it arrived this morning and it RATTLES (many hours of fun for small children but not a wanted feature for a PSU)

Current thoughts are some sort of 5V mains charger, or running it off of the 300W ATX powersupply that I already have stripped down to being a bench supply- nice stable 5V but it is a little large for me to be perminantly happy with that as a solution.

It would be nice to have some accessories that are guarenteed to work, or at least tested with, the RPi.

Hello All,

The RPi is certainly making a lot of people think about stuff they hadn't thought about before - if not in quite the way that was intended.

There is a slogan on my coffee cup "Good, Cheap, Quick - pick any two".

The RPi is certainly cheap but it looks as if the Good/Quick balance is just a little out on the power supply arrangement.

Based on observations made by contributors to this thread the problem is that the RPi really needs a 5.25 (+/- 0.2V) supply with a nice short thick lead (and hope that connector drop is not too bad) - Farnell could get whoever makes the Multicomp supplies they sell to make a special.

Other than that it's not going to be easy to fix cheaply if you don't want to solder- the obvious hack is to graft a suitable 5V supply (not  a USB charger) to a USB lead or solder it directly to the RPi but

I couldn't see any adjustable supplies in Farnell that cost less than the RPi.

This leaves you with the option of spending a lot or building/modding a supply.

Michael Kellett

Indeed Michael.

Unfortunately with the current generation of board, people will either have to follow the hardware hack articles, or else live with the existing state of affairs.

So far though, only 20k or so boards have been produced, which is a drop in the ocean compared to where the Pi is heading.  That makes it imperative that we help the Foundation and its partners address the issues so that Pi boards beyond v1.0 don't have quite the same level of power supply problems, and so that v2.0 boards eliminate this issue entirely through improved design.

It's an important task.  I'm a bit disappointed though that the Foundation's engineers aren't openly accepting the issue and collaborating with community engineers here to find a range of solutions.  The large amount of engineering experience within the community is a great resource.  It's odd that it's not being harnessed to its fullest extent.

My worst fear is that the Foundation is dragging its feet on recognizing the matter, possibly out of a totally mistaken worry about "egg on face".  No, the egg on face will come when there are millions of units out there, all with the same problem, resulting in many thousands of returns and adverse publicity.  Accepting it now and working openly on fixes would be both strategic and highly responsible of them, and would work very strongly to their advantage.

Morgaine.

http://www.amazon.co.uk/CostMad-Technology-Certified-Approved-Universal/dp/B005NZKTRG/ref=sr_1_16?ie=UTF8&qid=1337636414&sr=8-16

Have checked this at home with a couple of high wattage resistors-

5.24V Open Circuit dropping to

4.74V @ 460mA (10.3 ohms)

4.34V @ 860mA (5.0 ohms)

4.22V @ 1240 mA (3.4 ohms)

Not feeling all too confidant about this, but will give it a go when my SD card decides to make an apperance. Up side is that I now have a new Plan B, before Plan C (the ATX PSU) gets pulled out of retirement

Does seem that there are a couple of teething problems..... A "cheap and available to the masses" bit of kit needing top quality peripherals to function correctly seems to be missing the mark. Also that, so far, I've spent more on the bits to make the RPi function, than I have on the device it's self (and I'm still hedging my bets on a USB hub and case, and I already had the keyboard and mouse.... and the screen).

Jaz

What do you have connecting the power supply to your resistors?  According to my calculations, there's a 1.086 / 1.037 / 0.82 Ohm resistance between an ideal 5.24V voltage source and your test resistor.  It's either in the power supply itself (bad supply! bad supply!) or the wires connecting to your resistor (bad micro USB cable! bad micro USB cable!)