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by ceteras
Wed Oct 29, 2014 9:22 am
Forum: General discussion
Topic: noise through amp powered by 5v gpio
Replies: 7
Views: 2939

Re: noise through amp powered by 5v gpio

I've met this kind of noise before, it's a ground loop issue. In theory, all ground points are at the same voltage, but in reality this is not true. So it matters a lot where on the Pi you connect your amplifier ground connection. Try different places, I would recommend as close as possible to the p...
by ceteras
Fri Oct 10, 2014 11:48 am
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

The load on sync signals is not the same as on the RGB pins, so that math does not apply. For the 1bit part, you have 275 ohm in series with the 75ohm load inside the monitor, you get 350ohm load for each RGB pin. "A white screen would be 275 Ohm cumulatively for one bit through to 8 bit?" For each ...
by ceteras
Thu Oct 09, 2014 12:19 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

It is correct, but for 1bit version, you draw 9.45mA from the RGB pins.
This is not a problem by itself, but you might have to be careful what currents will the other GPIO pins have to source, as there is a limit for the total current on the GPIO bus.
by ceteras
Thu Oct 09, 2014 11:04 am
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

I don't understand how the sync series resistors were thought. The RGB signals are 75ohm impedance, but the sync lines are digital logic, and their requirements are pretty much similar to TTL. That is, a minimum voltage for logic "1" is 2.4V, and maximum voltage for logic "0" is 0.5V. This should sa...
by ceteras
Thu Sep 25, 2014 8:58 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

I've used an SN74HC04N to invert the DE signal and it worked. I've got some horizontal jittering on the image, it could be from the inverter chip or from my ~10cm long dpi wires (or maybe the ground layout). This would make a nice raspberry pi laptop, I believe it's the lowest-power solution for a g...
by ceteras
Thu Sep 25, 2014 1:32 pm
Forum: Other projects
Topic: first design for an hdmi to lvds adapter
Replies: 78
Views: 77997

Re: first design for an hdmi to lvds adapter

I'm not really sure I understand where's your level of expertise with electronics. If you had the eagle pcb files, would you be able to make your own pcb, then solder the parts? This chip in particular is a little difficult to solder because it has 0.5mm pin pitch and a ground exposed pad underneath...
by ceteras
Wed Sep 24, 2014 1:51 pm
Forum: HATs and other add-ons
Topic: HATless B+ possible? [solved]
Replies: 6
Views: 1575

Re: HATless B+ possible?

I've got my answer from HeBus' post here. One could setup a custom dt-blob.bin where the GPIO 0/1 are set to a particular function, and lose the HAT functionality without any side effects. pin@p0 { function = "dpi"; termination = "no_pulling"; }; // Pixel Clock pin@p1 { function = "dpi"; termination...
by ceteras
Wed Sep 24, 2014 1:48 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

Try active_low, for the sake of trying. I'm very interested in this too (but I only have a frequency counter, no scope, to test it). If it's still reversed, you could fix it with a fast inverter logic circuit (74F04 or something). Edit: pin@p16 { function = "output"; termination = "pull_up"; polarit...
by ceteras
Wed Sep 24, 2014 1:28 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

Hi, pin@p0 { function = "dpi"; termination = "no_pulling"; }; // Pixel Clock pin@p1 { function = "dpi"; termination = "no_pulling"; }; // Data Enable Anyone can confirm this? Somebody knows how to change output polarity (maybe through device tree dts/dtb)? Have you tried something like this? pin@p1...
by ceteras
Wed Sep 24, 2014 9:43 am
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

With driver for this is there any control over the frequency of the outputed signal? If so could it be slowed down to produce a lower resolution display thats at the 15Khz with a 50 to 60hz refresh rate to produce a signal compatible with an old CRT screen via the RGBS input on its SCART connector ...
by ceteras
Mon Sep 22, 2014 5:59 pm
Forum: HATs and other add-ons
Topic: HATless B+ possible? [solved]
Replies: 6
Views: 1575

Re: HATless B+ possible?

The documentation explicitly states not to connect anything to this i2C bus! I expect the reason is the designers do not want anything to interfere with HAT EEPROM detection that is built into the software, even when no HAT is used. Of course, I know what the documentation explicitly states, that's...
by ceteras
Mon Sep 22, 2014 1:50 pm
Forum: HATs and other add-ons
Topic: HATless B+ possible? [solved]
Replies: 6
Views: 1575

HATless B+ possible? [solved]

Hi, Is there a way to have the whole HAT mechanism disabled so one could use the two pins as they wish, without worries? I'm assuming the case where no HAT board is installed on the B+. Obviously, one could setup those pins as required by their application, but can this conflict with the original HA...
by ceteras
Fri Sep 19, 2014 2:12 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

Gert's VGA adapter is an application for an interface called DPI which became available since B+ . This is what I've called a DPI port. It's a parallel display interface. Very similar to a standard interface used in LCD panels. I mean LCD panels, not LCD displays/monitors. The trick is that for LCD ...
by ceteras
Fri Sep 19, 2014 1:59 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

RaTTuS wrote: only the RPi foundation - as they have access to all the internal bits to make it work -
You mean they did a prototype LCD on the DSI port.
I'm talking about connecting an LCD panel to the DPI port which is used for the VGA interface, did they do that too?
by ceteras
Fri Sep 19, 2014 1:52 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

Has anybody succeed connecting an LCD panel to the DPI port? I've tried two variants and both failed. One 480x272 4.3" parallel interfaced display and one 1024x768 lvds with a transmitter adapter. I've got a lot more troubleshooting to do, so I won't post questions about it yet. I'd like to know som...
by ceteras
Wed Sep 17, 2014 12:13 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

If DSI is display serial interface, it only makes sense for DPI to be "parallel"...
Anyway, you don't really find out anything about its existence any way you look it up in the internet.
by ceteras
Wed Sep 17, 2014 11:01 am
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

I believe it's Display Parallel Interface.
by ceteras
Tue Sep 16, 2014 5:20 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

Is there a way to set up the resolution on DPI port to custom values, such as 480x272, for using with a smaller LCD screen?
by ceteras
Thu Sep 11, 2014 6:21 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

There is no need for specific driver support. As all the pins are driven by hardware the signals ARE already present. They just don't come out until you set the GPIO pins to DPI mode. Now if you read the manual very carefully you should be able to find out how to get these signals out. Hint: look a...
by ceteras
Thu Sep 11, 2014 4:02 pm
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

mikronauts wrote:Thanks jdb!

Can I request driver support for the PCLK and DE?
[...]
+1
by ceteras
Thu Sep 11, 2014 10:02 am
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

I'd rather have the functionality than the HAT. I hope it's not going to be very difficult to enable those pins.
by ceteras
Thu Sep 11, 2014 8:39 am
Forum: HATs and other add-ons
Topic: Gert's VGA add-on for the B+
Replies: 240
Views: 117187

Re: Gert's VGA add-on for the B+

[...] Is there an accessible dot clock and display enable on the GPIO header, to allow driving LCD panels? [...] I'm also interested in this. The two pins are crucial for connecting lcd screens. If they're not available, the signals can be extracted from syncs using some PLL magic, but that's tricky.
by ceteras
Thu Jul 17, 2014 2:55 pm
Forum: Compute Module
Topic: Compute Module Test Board
Replies: 108
Views: 33162

Re: Compute Module Test Board

It took 25 seconds to draw on a core i7 2600 (3.4GHz). Amazing! At first, I didn't wait that long. The board itself is interesting. I would put the crystal closer to the LAN9512, usually it's a requirement, to put it as close as possible. The upper usb connector could be safely moved upwards. Are yo...
by ceteras
Thu Jul 17, 2014 2:00 pm
Forum: Compute Module
Topic: Compute Module Test Board
Replies: 108
Views: 33162

Re: Compute Module Test Board

Am I the only one who gets an empty pdf at the link above?
by ceteras
Tue Jul 15, 2014 2:03 pm
Forum: General discussion
Topic: The Raspberry Pi Model B+ Q&A thread
Replies: 388
Views: 183856

Re: The Raspberry Pi Model B+ Q&A thread

I'm very interested in the Secondary Memory Interface (SMI), and I know I'll have to wait for the specs for it. The SMI bus is using GPIO0 and GPIO1 (ID_SD and ID_SC, SA5 and SA4 in SMI). So, will it be possible to use SMI after its documentation is made public? Or, can GPIO[0,1] be used for other p...

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