MrBool
Posts: 104
Joined: Sat Jul 05, 2014 9:51 am

Raspberry Pi B+ schematic

Wed Jul 16, 2014 10:19 am

Why schematic of Raspberry Pi B+ is not available?

Here is only reduced schematics:
http://www.raspberrypi.org/documentatio ... ematics.md

BMS Doug
Posts: 3824
Joined: Thu Mar 27, 2014 2:42 pm
Location: London, UK

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 10:26 am

Is it the mechanical specs that you are interested in? there are more links on the blog post
Doug.
Building Management Systems Engineer.

MrBool
Posts: 104
Joined: Sat Jul 05, 2014 9:51 am

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 11:33 am

I am interested in the electrical schematic. I can't find it. Thank you.

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23398
Joined: Sat Jul 30, 2011 7:41 pm

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 12:38 pm

MrBool wrote:I am interested in the electrical schematic. I can't find it. Thank you.
Although it will be made available, it hasn't been published yet. Sorry.

Have you got a specific question that could be answered here?
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
"My grief counseller just died, luckily, he was so good, I didn't care."

opt928i
Posts: 1
Joined: Wed Jul 16, 2014 2:16 pm

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 3:33 pm

I'm also interested in the model B+ schematics.

On the B+ model there seems to be only a single crystal oscillator on the back of the circuit board, an AEL 19.2Mhz component near the processor labelled X1. On the B there are two crystal oscillators: AEL 19.2Mhz and AEL 25.000Mhz labelled X2 and X1 respectively. The model B schematics indicates the 25Mhz crystal is used by the Ethernet controller LAN9512.

I'm interested to know why the B+ model would no longer need a crystal oscillator for its Ethernet controller. I can see that it has been upgraded to a LAN9514 to provide four ports on the B+ but I cannot find anything in the component details or reference schematics to indicate why the crystal would no longer be needed.

User avatar
Burngate
Posts: 5972
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore
Contact: Website

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 3:43 pm

I don't know about MrBool, but I've got so many questions I'm probably better off waiting for the full sheet.
(note to self - patience is a virtue, it must be 'cos my mommy told me)

plugwash
Forum Moderator
Forum Moderator
Posts: 3439
Joined: Wed Dec 28, 2011 11:45 pm

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 3:47 pm

opt928i wrote: I'm interested to know why the B+ model would no longer need a crystal oscillator for its Ethernet controller. I can see that it has been upgraded to a LAN9514 to provide four ports on the B+ but I cannot find anything in the component details or reference schematics to indicate why the crystal would no longer be needed.
As I understand it the USB hub with ethernet is now clocked by a line from the main SoC.

MrEngman
Posts: 3844
Joined: Fri Feb 03, 2012 2:17 pm
Location: Southampton, UK

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 7:43 pm

How did the board layout people produce the PCB without the full schematic then?

There must surely be one somewhere.



MrEngman
Simplicity is a prerequisite for reliability. Edsger W. Dijkstra

Please post ALL technical questions on the forum. Please Do Not send private messages.

jdb
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2076
Joined: Thu Jul 11, 2013 2:37 pm

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 8:24 pm

MrEngman wrote:How did the board layout people produce the PCB without the full schematic then?

There must surely be one somewhere.



MrEngman
Because the board layout people and the designers are the same person. The one-man PCB design machine whom you feed ideas and out pops a BoM and a set of Gerbers.
Rockets are loud.
https://astro-pi.org

User avatar
mahjongg
Forum Moderator
Forum Moderator
Posts: 12130
Joined: Sun Mar 11, 2012 12:19 am
Location: South Holland, The Netherlands

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 8:35 pm

plugwash wrote:
opt928i wrote: I'm interested to know why the B+ model would no longer need a crystal oscillator for its Ethernet controller. I can see that it has been upgraded to a LAN9514 to provide four ports on the B+ but I cannot find anything in the component details or reference schematics to indicate why the crystal would no longer be needed.
As I understand it the USB hub with ethernet is now clocked by a line from the main SoC.
Yeah, I came to the same conclusion by looking at the early pictures, and so I inquired by people in the know. And yes, I can confirm that the 25.000 MHz crystal is removed in the B+, and the 25.000 MHz signal is now produced by the SoC. Which is brilliant because one of the weaknesses of the old design was that somehow the 25.000 MHz LAN9512 crystal (not crystal oscillator) was a bit less reliable than the 19.200 MHz SoC crystal, and once in a blue moon someone had a PI where the 25 MHz crystal halted, and had to be re-soldered to start up again.

The designer has killed two birds with one stone, because together with removing the crystal the design weakness was also removed, while at the same time some dimes were saved by not needing a relatively expensive component.

This obviously helped to be able to produce a board with many extra's for the same price! Improving reliability by removing expense! That's the way to do it! :P

plugwash
Forum Moderator
Forum Moderator
Posts: 3439
Joined: Wed Dec 28, 2011 11:45 pm

Re: Raspberry Pi B+ schematic

Wed Jul 16, 2014 10:45 pm

jdb wrote:Cookie to the first person that reverse-engineers the schematic (with reasonable accuracy).

I'm still waiting on an explanation from someone in the community as to the operation of the ideal diode on the 5V input.
Afaict it works as follows (caling the voltages on the two sides Vleft and Vright reffering to their positions on the schematic.

The left hand transistor is wired in such a way that it's base and emmitter will sit one base-emitter drop below Vleft.

If vleft > vright then the right hand transistor will be turned off and R3 will pull down the gate of the mosfet allowing current to flow with very little volt drop.
On the other hand if vright > vleft the right hand transistor will be turned on. The gate of the mosfet will be dragged up to very nearly vright. turning it off and blocking reverse current flow.

The two transistors in U14 are very closely matched and bipolar transistors have a VERY steep voltage response to base voltage, so these behaviours are triggered by tiny changes in the voltage across the device and hence you get an effect that is far closer to an ideal diode than any real diode is. The downside is you have small currents constantly flowing to ground so this isn't a great circuit for low power battery applications (the Pi is sufficiently power hungry that you won't notice an extra hundred microaps but it's something to be aware of if you are considering copying this design).

User avatar
Burngate
Posts: 5972
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore
Contact: Website

Re: Raspberry Pi B+ schematic

Thu Jul 17, 2014 10:11 am

I'd go along with that explanation, though I'd mention the similarity to a classic current-mirror.*

The major problem I see is that it doesn't mention the FET's characteristics, which seem rather important.
The fact that its gate threshold is between -0.5 & -0.9v is significant - it's close to one base-emitter drop, so when vleft = vright, the FET is close to turn-on.
Also, no mention is made of the fact that under normal conditions it's working back-to-front: although Vgs is negative, correct for a P-FET, Vds is positive, with current flowing drain-source, which isn't the normal way of doing things (quite valid for a FET, though not for a bipolar transistor).
What that means is you can't just look at the datasheet - it has plenty of graphs showing what happens while Ids is standard (for a P-channel) negative, but not the reverse.

*How concise can an explanation be and still merit a cookie? Could one word suffice, if that word is "Google"?

User avatar
Burngate
Posts: 5972
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore
Contact: Website

Re: Raspberry Pi B+ schematic

Thu Jul 17, 2014 10:32 am

I've been wondering how best to explain a current mirror

It seems to consist of two halves.
One half uses the high current gain of a bipolar transistor to produce a base-emitter voltage of just the right value to allow the transistor to pass the required collector current (neglecting the much smaller base current)
The other half uses that voltage to bias another transistor so that it has the same collector current (again neglecting the base current, which comes from the first half)

It does rely on the two transistors having similar Vbe curves, and also on there being no change to Vbe when Vce changes.

One can create a current mirror with dissimilar transistors if one puts a resistor in each emitter. This increases the effective Vbe, and so reduces the effect of the actual Vbe.

GadgetUK
Posts: 61
Joined: Thu Jan 19, 2012 6:02 pm

Re: Raspberry Pi B+ schematic

Thu Jul 17, 2014 10:51 am

If you want more detail about the power supply input then take a look at this page from adafruit which covers it quite nicely.

https://learn.adafruit.com/introducing- ... wer-supply

User avatar
mikronauts
Posts: 2717
Joined: Sat Jan 05, 2013 7:28 pm
Contact: Website

Re: Raspberry Pi B+ schematic

Thu Jul 17, 2014 2:17 pm

I'd really like a full listing of the test points on the back with Broadcom pin number & functionality.
jamesh wrote:
MrBool wrote:I am interested in the electrical schematic. I can't find it. Thank you.
Although it will be made available, it hasn't been published yet. Sorry.

Have you got a specific question that could be answered here?
http://Mikronauts.com - home of EZasPi, RoboPi, Pi Rtc Dio and Pi Jumper @Mikronauts on Twitter
Advanced Robotics, I/O expansion and prototyping boards for the Raspberry Pi

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23398
Joined: Sat Jul 30, 2011 7:41 pm

Re: Raspberry Pi B+ schematic

Thu Jul 17, 2014 2:55 pm

mikronauts wrote:I'd really like a full listing of the test points on the back with Broadcom pin number & functionality.
jamesh wrote:
MrBool wrote:I am interested in the electrical schematic. I can't find it. Thank you.
Although it will be made available, it hasn't been published yet. Sorry.

Have you got a specific question that could be answered here?
Why?
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
"My grief counseller just died, luckily, he was so good, I didn't care."

User avatar
mikronauts
Posts: 2717
Joined: Sat Jan 05, 2013 7:28 pm
Contact: Website

Re: Raspberry Pi B+ schematic

Thu Jul 17, 2014 3:35 pm

To see if any more functionality is exposed.

I realize they are not meant for more I/O, but for some projects (one-offs) it would be interesting to experiment with them - and they may give me a head start on using the extra I/O until I get my hands on a Compute Module and make my own breakout.

Looking at canada.newark.com I doubt I can get a compute module development kit before August or September this year :-(

Which delays designing boards around the Compute Module. I have 30+ years of experience in industrial control, and can see many uses for it... the question is, would the products sell?

Love the B+ so far!
jamesh wrote: Why?
http://Mikronauts.com - home of EZasPi, RoboPi, Pi Rtc Dio and Pi Jumper @Mikronauts on Twitter
Advanced Robotics, I/O expansion and prototyping boards for the Raspberry Pi

jamesh
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 23398
Joined: Sat Jul 30, 2011 7:41 pm

Re: Raspberry Pi B+ schematic

Thu Jul 17, 2014 4:51 pm

mikronauts wrote:To see if any more functionality is exposed.
I don't believe there is. Test points are generally there to tests the stuff that is exposed to ensure it works.

There might be some others, but I cannot think what they might be.
Principal Software Engineer at Raspberry Pi (Trading) Ltd.
Contrary to popular belief, humorous signatures are allowed. Here's an example...
"My grief counseller just died, luckily, he was so good, I didn't care."

NoSuchNick
Posts: 42
Joined: Tue Sep 20, 2011 1:38 pm

Re: Raspberry Pi B+ schematic

Wed Jul 23, 2014 9:41 pm

From some pictures it looks like the JTAG interface is brought out to an 8-signal connector J5 on the back of the pi. From the footprint, the connector looks mechanically similar to an HDMI or Mini USB socket.

So I was wondering:

- What kind of socket is this?
- Is there any use for the JTAG interface for a general developer / when poking around on an driver / kernel module level
- Is this just some leftovers from the development process?

jdb
Raspberry Pi Engineer & Forum Moderator
Raspberry Pi Engineer & Forum Moderator
Posts: 2076
Joined: Thu Jul 11, 2013 2:37 pm

Re: Raspberry Pi B+ schematic

Wed Jul 23, 2014 10:15 pm

NoSuchNick wrote:From some pictures it looks like the JTAG interface is brought out to an 8-signal connector J5 on the back of the pi. From the footprint, the connector looks mechanically similar to an HDMI or Mini USB socket.

So I was wondering:

- What kind of socket is this?
- Is there any use for the JTAG interface for a general developer / when poking around on an driver / kernel module level
- Is this just some leftovers from the development process?
It's there so I don't have to faff around with 6 jumper wires between my JTAG dongle and the board whenever I want to see what's happening inside the chip. It's a solder pad arrangement for an FFC connector - most of the B+ Pis I have for development have had this connector soldered on.

The pins are connected to the Videocore JTAG interface like they were on the B (the two unpopulated headers in the middle of the board). There is no access to the ARM JTAG so it's pretty much useless to anyone that doesn't have the Broadcom toolchain/software for VC debug.
Rockets are loud.
https://astro-pi.org

bbodin
Posts: 70
Joined: Sat Jun 28, 2014 3:23 pm

Re: Raspberry Pi B+ schematic

Wed Jul 23, 2014 11:25 pm

I found the version 1.0 schematic diagram for B+here. Note that the simplified schematic version is 1.2.

Mod edit: nuked link.
Binh Bui

User avatar
AndrewS
Posts: 3625
Joined: Sun Apr 22, 2012 4:50 pm
Location: Cambridge, UK
Contact: Website

Re: Raspberry Pi B+ schematic

Thu Jul 24, 2014 12:01 am

bbodin wrote:I found the version 1.0 schematic diagram for B+ DELETE. Note that the simplified schematic version is 1.2.
Wow :shock:
Note however that the simplified schematic is Rev 1.2 which matches the Rev 1.2 of the Model B+ boards currently being sold.

I noticed that on the "Rev 1.0" schematic the AV-connector has the Video and GND pins swapped around - who knows what other changes there might have been between Rev1.0 and Rev1.2, so probably best to not put too much faith into it? :?

User avatar
AndrewS
Posts: 3625
Joined: Sun Apr 22, 2012 4:50 pm
Location: Cambridge, UK
Contact: Website

Re: Raspberry Pi B+ schematic

Thu Jul 24, 2014 10:33 pm

GadgetUK wrote:If you want more detail about the power supply input then take a look at this page from adafruit which covers it quite nicely.

https://learn.adafruit.com/introducing- ... wer-supply
Even that (still) says "There is a PNP-matched-pair action going on around the polarity FET, but its 3AM and I'm not 100% sure what it's for so I'll wait till I get some rest before doing any analysis." ;)

johnclord
Posts: 3
Joined: Fri Jul 25, 2014 1:35 am

Re: Raspberry Pi B+ schematic

Fri Jul 25, 2014 1:38 am

MrBool wrote:Why schematic of Raspberry Pi B+ is not available?

Here is only reduced schematics:
http://www.raspberrypi.org/documentatio ... ematics.md
Got a 404 error on that link

User avatar
Burngate
Posts: 5972
Joined: Thu Sep 29, 2011 4:34 pm
Location: Berkshire UK Tralfamadore
Contact: Website

Re: Raspberry Pi B+ schematic

Fri Jul 25, 2014 8:34 am

johnclord wrote:Got a 404 error on that link
http://www.raspberrypi.org/documentatio ... /README.md

Return to “General discussion”