Raspberry Pi Gets VGA, Dual Screen Support

VGA

The Broadcom SOC in the Raspberry Pi is actually surprisingly powerful, it turns out. It’s actually capable of driving a VGA monitor through the GPIO pins using a handful of resistors.

[Gert van Loo], Raspberry Pi chip architect, wizard, and creator of a number of interesting expansion boards showed off a VGA adapter for the new B+ model at the recent Raspberry Pi Jam in Cambridge this week. Apparently, there is a parallel interface on the SoC that can be used to drive VGA with hardware using a resistor ladder DAC. That’s native VGA at 1080p at 60 fps in addition to HDMI for the Raspberry Pi. Only the new Model B+ has enough pins to do this, but it’s an intriguing little board.

The prospect of having two displays for a Raspberry Pi is very interesting, and the remaining four GPIOs available mean a touch screen could be added to one display, effectively making a gigantic Nintendo DS. Of course there are more practical problems a dual display Raspi solves, like driving a projector for the current crop of DSP/resin 3D printers, while still allowing for a usable interface during a print.

The VGA expansion board, “is likely to have issues with EMC,” which means this probably won’t be a product. Getting a PCB made and soldering SMD resistors isn’t that hard, though, and we’ll post an update when the board files are released.

Thanks [Uhrheber] for sending this one in.

Hacking VGA for Trippy Video Effects

RGB.VGA.VOLT

Ever since flat panel LCD monitors came on the scene, most old CRTs have found their ways into the garbage or into the backs of closets. For this project, it might be a good idea to pull out the old monitor or TV out and dust it off! [James] has found a way to hack the VGA input to these devices to get them to display vivid visualizations based on an audio input.

The legacy hardware-based project is called RGB.VGA.VOLT and works by taking an audio signal as an input, crossing some wires, and sending the signal through a synthesizer. The circuit then creates a high-frequency waveform that works especially well for being displayed on VGA. The video can also be channeled back through an audio waveform generator to create a unique sound to go along with the brilliant colors.

[James]‘s goals with this project are to generate an aesthetic feeling with his form of art and to encourage others to build upon his work. To that end, he has released the project under an open license, and the project is thoroughly documented on his project site.

There have been plenty of hacks in the past that have implemented other protocols with VGA or implemented VGA on microcontrollers, but none that have hacked the interface entirely to create something that looks like the Star Gate sequence from 2001: A Space Odyssey. We think it’s a great piece of modern art and a novel use of VGA!

Thanks for the tip, [Kyle]!

THP Entry: A CPLD Video Card With VGA And NTSC

NTSC

[PK] is working on a very simple video card, meant to output 640×480 VGA with a cheap CPLD. The interface will be 5 Volt SPI, meaning there’s a ton of potential here for anyone wanting put a reasonable (and cheap) display in a microcontroller project. The project has come a long way, and his latest update showcases something that has only been done once before: color NTSC with programmable logic

The brains of the outfit is a $5, 100-pin CPLD from Xilinx. Apart from that, the rest of the components are a crystal, PLL, and an almost hilarious number of resistors for the R2R ladder. The one especially unique component is the 25.056815 MHz crystal – multiply by that by two, and it’s fast enough to drive a VGA monitor. Divide the crystal by seven, it’s the 3.579545 MHz you need for an NTSC colorburst frequency. That’s VGA and NTSC in a single programmable logic project, something the one FPGA project we could find that did color NTSC couldn’t manage.

The next step in the project is designing a PCB and figuring out the code for the framebuffer. [PK] put up a demo showing off both VGA and NTSC; you can check that out below.


SpaceWrencherThe project featured in this post is an entry in The Hackaday Prize. Build something awesome and win a trip to space or hundreds of other prizes.

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I2C From Your VGA Port

Breakout board for VGA to I2C

VGA, DVI, and HDMI ports use Display Data Channel (DDC) to communicate with connected displays. This allows displays to be plug and play. However, DDC is based on I2C, which is used in all kinds of electronics. To take advantage of this I2C port on nearly every computer, [Josef] built a VGA to I2C breakout.

This breakout is based on an older article about building a $0.25 I2C adapter. This adapter hijacks specific lines from the video port, and convinces the kernel it’s a standard I2C device. Once this is done, applications such as i2c-tools can be used to interact with the port.

[Josef] decided to go for overkill with this project. By putting an ATmega328 on the board, control for GPIOs and LEDs could be added. Level shifters for I2C were added so it can be used with lower voltage devices. The end product is an I2C adapter, GPIOs, and LEDs that can be controlled directly from the Linux kernel through an unused video port.

640×480 VGA On An Arduino

VGAThere are dozens, if not hundreds of examples around the Intertubes of an Arduino generating a VGA video output. The Arduino isn’t the fastest chip by far, and so far, all of these VGA generation techniques have peaked out at lower resolutions if you want to control individual pixels.[PK] has an interesting technique to generate 640×480 VGA at 60 frames per second without overclocking. It’s hacky, it’s ugly, but surprisingly, it actually works.

The VGA standard of 640×480 @ 60 fps requires pixels to be clocked out at 25.175 MHz, and the ATMega chips found in Arduinos top out at 20 MHz. [PK] wanted to generate VGA signals without overclocking, He did this by doubling the clock frequency with digital logic. The ATMega generates a clock, an inverter delays that clock so it is 90 degrees out of phase, and the two clocks are XORed, doubling clock output of the micro. It produces a very ugly square wave at 32 MHz – an error of 27% compared to the VGA spec. Somehow it still works.

With a hilariously out of spec clock, the rest of the project was pulled together from [Nick Gammon]‘s VGA library, a 16×16 font set, and a project from [lft]. Video below.

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Vector Display Output on an Oscilliscope

V3zirb1

What can we say, we’re a sucker for projects featuring our logo. That being said, this one is seriously awesome. [CNLohr] has figured out how to create a vector display output on an oscilloscope… from a VGA port.

He was inspired by a game called Trace Vector, which is done in the same style as some of the old classics like Asteroids. This got [Charles] thinking, and he decided to see what it would take to make his own vector capable display. An oscilloscope is perfect for this, as it already works by controlling the position of the beam (like a vector), as opposed to standard LCDs and CRTs that use rasterizing (horizontal scanning). This means to get the oscilloscope to display a graphic, all you need to do is to vary the voltages going into the X and Y channels — well, at a high speed!

But where are you going to find such a high speed digital to analog converter? Oh yeah, your computer’s VGA port! For a few dollars [Charles] threw together a VGA adapter with a few resistors using just the red and blue outputs (source code). A bit of programming later, and he’s created his own vector display!

Stick around to see our lovely skull and cross-wrenches rotate on his oscilloscope! Oh, and for a more in depth explanation and more impressive vector video demonstration.

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Update From Wayback: AVGA Reborn as RetroWiz

retrowiz-vga-avr-gaming-system

This one has been a long time coming. We’re finally seeing an update to [Jaromir's] retro gaming platform based around and ATmega chip. The thing that was novel about it back in 2009, and continues to be to this day, is the use of VGA output (PAL) from an AVR chip rather than composite video like most offerings.

Good projects never die and recently he picked the hardware up again, spinning a mostly surface mount board and putting together a new website to feature his work. Above you can see a demo of Commander Keen 4 running on the hardware (video below). He’s also has a rather trippy Super Mario port and adapted [Albert Seward's] PacMan source for the hardware.

The chip is being clocked at 32MHz with VGA clock running at 19.6608 MHz. This gives him sixteen colors with a resolution of 192×144. He concedes that you get better resolution out of composite video, but who needs resolution for retro gaming?

[Read more...]

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