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by simonbr
Thu May 25, 2017 9:08 pm
Forum: HATs and other add-ons
Topic: Geekworm ups pi hat
Replies: 60
Views: 34410

Re: Geekworm ups pi hat

Hi Fermars, thank you! Following your suggestion, I added an article on my website describing a relatively simple modification of the UPS board. I hope it is of use to you and others. Check out https://brousant.nl/jm3/elektronica/105-geekworm-ups-for-raspberry-pi-simple-modification-detailed Also, I...
by simonbr
Sat May 20, 2017 3:10 pm
Forum: HATs and other add-ons
Topic: Geekworm ups pi hat
Replies: 60
Views: 34410

Re: Geekworm ups pi hat

Hi all, For your information, I published an article about an ongoing project with this UPS board on my website. It contains various technical details, such as a reverse engineered circuit diagram. The article also suggests how the board might be modified to enhance its functions. Let me know what y...
by simonbr
Wed Aug 14, 2013 7:32 am
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

No wanting to hijack a thread and I will be glad to have this moved if appropriate but our org is having similar/same issues with USB on rev2 Pis. ... A USB "cut-out" issue is causing problems with our install on rev2s (no F1 or F3...but still the 47.5 C32 polyfuse) which I know is power related bu...
by simonbr
Mon Jul 23, 2012 8:06 am
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

Actually I'll have to disagree with this. Is that opinion due to actual experience with contract manufacturing in the Far East? No we're a bit south of there what about you? I have experience with two contract manufacturers in China, a medium sized and a big one, and they both require us to specify...
by simonbr
Sun Jul 22, 2012 4:46 pm
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

bazza14 wrote: Actually I'll have to disagree with this.
Is that opinion due to actual experience with contract manufacturing in the Far East?
by simonbr
Sat Jul 21, 2012 9:17 pm
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

I can't imagine they'd insist on a specific part number, so the manufacturers would be free to select the actual device used with any limits specified by the design. In fact it is normal in large scale production that you have to specify the exact parts. A serious production company would never use...
by simonbr
Thu May 31, 2012 10:02 pm
Forum: Troubleshooting
Topic: Trouble using WG111T
Replies: 4
Views: 2410

Re: Trouble using WG111T

Looks like the kind of errors I had with my wifi adapter.

See http://www.raspberrypi.org/phpBB3/viewt ... =24&t=5830

Best regards
Simon
by simonbr
Wed May 30, 2012 8:05 am
Forum: Troubleshooting
Topic: Ethernet chip gets raging hot
Replies: 86
Views: 30800

Re: Ethernet chip gets raging hot

Yes FOV taken into account.. Just to satistfy the weird people who think fingers are thermomters I can held my finger on the new board I got from Farnell. IR thememeter Ambient 25.1C CPU 48.9C Eth 50.8 These values are quite different from what you reported earlier... Best regards Simon I had notic...
by simonbr
Wed May 30, 2012 7:49 am
Forum: Troubleshooting
Topic: Ethernet chip gets raging hot
Replies: 86
Views: 30800

Re: Ethernet chip gets raging hot

There IS a heat problem if the chip is meant to be running at or below 30C. According to the data sheet, its operating temperature specification is up to 70 degC (assuming the commercial type is mounted). I have the impression that as reported in this topic, the chip doesn't get as hot as that. I w...
by simonbr
Tue May 29, 2012 9:23 pm
Forum: Troubleshooting
Topic: Ethernet chip gets raging hot
Replies: 86
Views: 30800

Re: Ethernet chip gets raging hot

spurious wrote:Yes FOV taken into account..
Just to satistfy the weird people who think fingers are thermomters I can held my finger on the new board I got from Farnell.
IR thememeter
Ambient 25.1C
CPU 48.9C
Eth 50.8
These values are quite different from what you reported earlier...

Best regards
Simon
by simonbr
Tue May 29, 2012 8:55 pm
Forum: Troubleshooting
Topic: Is this partitioning advice correct
Replies: 11
Views: 2555

Re: Is this partitioning advice correct

In the Debian image, the line in /etc/fstab specifying the swap partition is commented out, so it is actually not used and you can remove the swap partition from the sd card without consequence. I think that to use a swap partition on a hard disk it is sufficient to specify that in /etc/fstab using ...
by simonbr
Tue May 29, 2012 2:01 pm
Forum: Troubleshooting
Topic: Ethernet chip gets raging hot
Replies: 86
Views: 30800

Re: Ethernet chip gets raging hot

if we can trust them to use their IR thermometers And if we can trust them to use their IR thermometers correctly... these measure the temperature averaged over a circular area with a size that depends on measuring distance and FOV. This chip is so small that it may be difficult to accurately get i...
by simonbr
Tue May 29, 2012 9:55 am
Forum: Troubleshooting
Topic: Ethernet chip gets raging hot
Replies: 86
Views: 30800

Re: Ethernet chip gets raging hot

I am intrigued how a finger is a good measure of a chip working in-spec of the temperature range it can handle? The machine is just that.. keep your fingers off it.. it's electrical.. would you put you fingers into the back of your TV if the back was off? Fingers conduct, so can short things out.. ...
by simonbr
Mon May 28, 2012 10:11 am
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

If you think about it, a chargers only real job is to charge a battery safely which is usually c/10 or a 10th of the battery's mah capacity. That is not correct, nowadays most portable devices use lithium-ion batteries, which accept a maximum charge current of about C, i.e. some 1A or more for a ty...
by simonbr
Sun May 27, 2012 9:02 am
Forum: Troubleshooting
Topic: Wiki for cross compiling kernel on Ubuntu fails on line 1
Replies: 2
Views: 1676

Re: Wiki for cross compiling kernel on Ubuntu fails on line

You can install it on 10.04 Lucid by

$ sudo add-apt-repository ppa:linaro-maintainers/toolchain
$ sudo apt-get update
$ sudo apt-get install gcc-arm-linux-gnueabi

See also https://launchpad.net/~linaro-maintaine ... /toolchain

Best regards
Simon
by simonbr
Sat May 26, 2012 11:02 pm
Forum: Troubleshooting
Topic: Ethernet chip gets raging hot
Replies: 86
Views: 30800

Re: Ethernet chip gets raging hot

I tried to find the thermal resistance of the QFN package at smsc.com but couldn't. I found a datasheet of another component with the QFN64 package that says 20 degC/W typical without airflow. This assumes the use of 49 (7*7) thermal vias of 0.3mm diameter. At 3/4W the die temperature would rise 15...
by simonbr
Fri May 25, 2012 7:28 pm
Forum: General discussion
Topic: Serial Port Adapter Compatibility
Replies: 10
Views: 4353

Re: Serial Port Adapter Compatibility

At the end of the boot I'm presented with a login prompt. However, when I type anything nothing appears on the screen. Before I start testing my connections and board is this something anyone else has seen? I connected a serial interface to the GPIO connector. It uses the FT232RQ USB-to-serial chip...
by simonbr
Sun May 20, 2012 8:15 am
Forum: Troubleshooting
Topic: Iphone 4 Power Adapter Problem
Replies: 17
Views: 5826

Re: Iphone 4 Power Adapter Problem

Looking at the schematics: http://www.raspberrypi.org/wp-content/uploads/2012/04/Raspberry-Pi-Schematics-R1.0.pdf you can see that TP1 is placed after fuse F3. That fuse can have a resistance of around 0.4 ohms. The current consumption of a Pi will be around 0.4A, and some more with USB devices conn...
by simonbr
Fri May 18, 2012 7:54 am
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

...to make F1 and F2 take power not from the board's +5V rail but directly from the charger input (same as F3). Morgaine. Then, using the current type of fuses for F1 and F2, and assuming a 3% accurate input voltage, the minimum USB voltage would be 4.25V, still considerably lower than the USB spec...
by simonbr
Thu May 17, 2012 6:33 pm
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

I have spent some more thought on this subject. It looks like quite a number of users are running into problems where (combinations of) USB devices, that should on first sight be acceptable, refuse to work with the Raspberry Pi. I suspect that the Raspberry Pi design does not comply to USB specifica...
by simonbr
Tue May 15, 2012 11:08 am
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

If however a higher than normal constant voltage is supplied to the main power input the TVS will limit the voltage and in doing so will produce excessive current through the fuse and trip it. Using the breakdown voltage of the TVS, the junction to ambient thermal resistance of the package, assumin...
by simonbr
Mon May 14, 2012 8:23 am
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

The USB2.0 spec allows low-powered ports to provide a Vbus of 4.4V minimum. So there is a reasonable margin for voltage drop on F1 and F2 at 100mA. Well not quite, if you take into account that the input power supply voltage may be slightly lower than 5.0 V. Assuming there are good reasons for keep...
by simonbr
Sun May 13, 2012 8:25 pm
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

It is also possible to make a "cheater" USB cable which takes a separate +5V power feed (essentially a poor-man's 1-port powered hub). That's almost what you did, except doing it on the board can present some other issues, eg. overloading the main input fuse and starving the Pi for voltage. Actuall...
by simonbr
Sun May 13, 2012 8:10 pm
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Re: Design flaw? Polyfuses for USB current limiting

Hi Gert, I'm sorry, but I don't agree with your statement that the resistance of the polyfuses will be negligible at 100 mA. As mentioned the polyfuses on my unit were a bit over 5 ohms (resistance measurement with a multimeter, not calculating from a voltage drop at significant current). Even at 10...
by simonbr
Sun May 13, 2012 6:28 pm
Forum: General discussion
Topic: Design flaw? Polyfuses for USB current limiting
Replies: 245
Views: 113399

Design flaw? Polyfuses for USB current limiting

Hi, I encountered what may be a problematic design flaw in the Raspberry Pi Model B. From the schematic, the output current of each USB port is limited to a nominal 140 mA using a miniSMDC014. Although limiting the current may be a good idea, the side effect is a large voltage drop. According to its...

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