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rurwin
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Re: Whats the point of Gpio pins?

Fri Apr 20, 2012 2:55 am

firstplacefranz said:


How are the pins numbered. In the Code on the wiki the GPIO pins are numbered, GPIO 1, GPIO 0, ect. What is the ordering of these pins? which is 0, and 1?



See the Low-level Peripherals page of the Wiki. The P1-nn number uses the ribbon cable numbering. So if you connect a ribbon cable to the pins using an IDC connector, core 1 (P1-01) is 3.3V and core 2 (P1-02) is 5V.

Assuming of course that you connect the cable the right way round.

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Re: Whats the point of Gpio pins?

Sun Apr 22, 2012 4:17 pm

I have successfully made a blinking led light... unfortunetly its not blue.

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Re: Whats the point of Gpio pins?

Sun Apr 22, 2012 4:19 pm

FirstPlaceFranz said:


I have successfully made a blinking led light... unfortunetly its not blue.


Check your program...

FoxTossing
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Re: Whats the point of Gpio pins?

Thu Apr 26, 2012 6:07 pm

I needed a quick test project, so knocked out a quick plugin blinkenlights board, since the RPi seems woefully underequipped in that department. 8 red/green LEDs, 8 resistors and a bit of header strip, on a single-layer easy-rules board. (the 3.3V supply is low enough that you can stick a red & and a green LED in series, and drive the middle node with a GPIO (through a resistor) to turn either, or neither, LED on.

According to quotes I was getting from PCB shops, it's about £5 all-in. Anyone want the design files / gerbers / built units? (I have access to a pick & place line, so if  few people want them, I'll run a panelsworth...)

Also, anyone know what current the IO pads are rated to, and how they respond to floating inputs? I don't care overmuch if they dissipate an extra 100uA when at half-mast, but if it's banned, I'll have to build a version with proper buffers)

[Image Can Not Be Found]

(Hmm, how's a chap supposed to post an image? Just imagine a screenshot of a 17x36mm PCB perched on the corner of a STEP model of a Raspberry Pi...)

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Re: Whats the point of Gpio pins?

Fri Apr 27, 2012 3:07 pm

FoxTossing said:


I needed a quick test project, so knocked out a quick plugin blinkenlights board, since the RPi seems woefully underequipped in that department. 8 red/green LEDs, 8 resistors and a bit of header strip, on a single-layer easy-rules board. (the 3.3V supply is low enough that you can stick a red & and a green LED in series, and drive the middle node with a GPIO (through a resistor) to turn either, or neither, LED on.

According to quotes I was getting from PCB shops, it's about £5 all-in. Anyone want the design files / gerbers / built units? (I have access to a pick & place line, so if  few people want them, I'll run a panelsworth...)

Also, anyone know what current the IO pads are rated to, and how they respond to floating inputs? I don't care overmuch if they dissipate an extra 100uA when at half-mast, but if it's banned, I'll have to build a version with proper buffers)

[Image Can Not Be Found]

(Hmm, how's a chap supposed to post an image? Just imagine a screenshot of a 17x36mm PCB perched on the corner of a STEP model of a Raspberry Pi...)


Hmmm, very interesting... sound like a plan, please post when you finish the breadboard
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Re: Whats the point of Gpio pins?

Fri Apr 27, 2012 5:47 pm

I posted details (a data sheet amendment) about the GPIO drive strength. It is now somewhere in the Wiki. Also if you read the BCM2835 section about GPIO you find a table with all ALT functions and that table also has column the pull-up/pulldown status after reset.

<Gert to the rescue again >

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Re: Whats the point of Gpio pins?

Fri Apr 27, 2012 7:48 pm

Gert said:


I posted details (a data sheet amendment) about the GPIO drive strength. It is now somewhere in the Wiki. Also if you read the BCM2835 section about GPIO you find a table with all ALT functions and that table also has column the pull-up/pulldown status after reset.

<Gert to the rescue again >



very cool, so when is your stuff ready for primetime?
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Re: Whats the point of Gpio pins?

Fri Apr 27, 2012 8:19 pm

Gert said:


I posted details (a data sheet amendment) about the GPIO drive strength.


Here are the relevant links, in case of interest:

http://elinux.org/RPi_Low-leve.....eripherals

http://www.scribd.com/doc/9135.....ds-Control

looks like drive strength is configurable from 2 mA to 16 mA

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Re: Whats the point of Gpio pins?

Fri Apr 27, 2012 8:26 pm

Since we're getting so much good tech info, I'm now tempted to ask what risetime / falltime I might expect from the SoC GPIO pins, with say 15 pF load. But I can wait to find that out when my own Pi arrives, I guess.

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Re: Whats the point of Gpio pins?

Fri Apr 27, 2012 8:30 pm

verrrry interrresting...love this edge of your seat stuff... its like the first pc again

sadly i was informed that i won't be eating my pi till mid august or so, so i cant celebrate with the chosen few till then
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Let your programming Fly

FoxTossing
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Re: Whats the point of Gpio pins?

Fri Apr 27, 2012 8:39 pm

Gert said:


Ah, thanks for the drive strengths. That just kicks it back onto the software, which is fair enough... I'll probably limit it to 5mA with the resistor anyway. That's plenty of current for an 0603 LED.

is there any chance you can do similar magic with the 'tolerates inputs at 1.5V or so' question? (Although a pad structure with that many drive strength options is unlikely to be too fragile... Any mention of hysteresis / Schmitt stages?)

I think I'll run a panel of the boards anyway, since I've got a new PCB manufacturer I want to try out, and I've not done V-grooved panelisation before, so a learning experience... Also it's a precursor to a CPLD motor controller board I want to make next.

I'm sure I can find someone in Cambridge to try one out before I populate the whole panel

Still can't find an image hosting site this forum likes...http://imageshack.us/photo/my-images/213/blinkyhr.jpg/ in the meantime. Not a complicated board!

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Re: Whats the point of Gpio pins?

Fri Apr 27, 2012 10:00 pm

FoxTossing said:

Still can't find an image hosting site this forum likes...
If you have a Google account try that. I was able to embed pictures from Google Picasa (now linked to, or possibly hosted within, GooglePlus)

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Gert van Loo
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Re: Whats the point of Gpio pins?

Sat Apr 28, 2012 10:53 am


Still can't find an image hosting site this forum likes…


You probably have the same problem I had which is that images did not seem to work. I found it is not the website, it is the way you set the link. Sevaral 'prepared' links from e.g. scribd or image shack don't work. There is always one which does work but it often takes me a few tries to get the right one.

This is how I do it:

Press the tree (insert/edit images) button. Then put the link text in the pop-pup window. After pressing 'insert' you will see if the image works. If it is a link that does not work it shows a tiny icon of a page torn in two. Delete it and start again with a different link text until it works.

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