Doing 1080p Video, Sort Of, On The STM32 Microcontroller

September 30, 2024 by Lewin Day 12 Comments

When you think 1080p video, you probably don’t think STM32 microcontroller. And yet! [Gabriel Cséfalvay] has pulled off just that through the creative use of on-chip peripherals. Sort of.

The build is based around the STM32L4P5—far from the hottest chip in the world. Depending on the exact part you pick, it offers 512 KB or 1 Mbyte of flash memory, 320 KB of SRAM, and runs at 120 MHz. Not bad, but not stellar.

Still, [Gabriel] was able to push 1080p at a sort of half resolution. Basically, the chip is generating a 1080p widescreen RGB VGA signal. However, to get around the limited RAM of the chip, [Gabriel] had to implement a hack—basically, every pixel is RAM rendered as 2×2 pixels to make up the full-sized display. At this stage, true 1080p looks achievable, but it’ll be a further challenge to properly fit it into memory.

Output hardware is minimal. One pin puts out the HSYNC signal, another handles VSYNC. The same pixel data is clocked out over R, G, and B signals, making all the pixels either white or black. Clocking out the data is handled by a nifty combination of the onboard DMA functionality and the OCTOSPI hardware. This enables the chip to hit the necessary data rate to generate such a high-resolution display.

There’s more work to be done, but it’s neat to see [Gabriel] get even this far with such limited hardware. We’ve seen others theorize similar feats on chips like the RP2040 in the Pi Pico, too. Video after the break.

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Dual-Port RAM For A Simple VGA Card

August 30, 2024 by Jenny List 7 Comments

Making microcontrollers produce video has long been a staple of hardware hacking, but as the resolution goes up, it becomes a struggle for less capable silicon. To get higher resolution VGA from an Arduino, [Marcin Chwedczuk] has produced perhaps the most bulletproof solution, to create dual-port RAM with the help of a static RAM chip and a set of 74-series bus transceivers, and let a hardware VGA interface take care of the display. Yes, it’s not a microcontroller doing VGA, but standalone VGA for microcontrollers.

Dual-port memory is a special type of memory with two interfaces than can independently be used to access the contents. It’s not cheap when bought in integrated form, so seeing someone making a substitute with off-the-shelf parts is certainly worth a second look. The bus transceivers are in effect bus-width latches, and each one hangs on to the state while the RAM chip services each in turn. The video card part is relatively straightforward, a set of 74 chips which produce the timings and step through the addresses, and a shift register to push out simple black or white pixel data as a rudimentary video stream. We remember these types of circuits being used back in the days of home made video terminals, and here in 2024 they still work fine.

The display this thing produces isn’t the most impressive picture, but it is VGA, and it does work. We can see this circuit being of interest to plenty of other projects having less capable processing power, in fact we’d say the challenge should lie in how low you can go if all you need is the capacity to talk 74-series logic levels.

Interested in 74-series VGA cards? This isn’t the first we’ve seen.

Simon Says With An RP2040

January 30, 2024 by Chris Lott No comments

The team of [Michael] and [Chimdi] from Cornell’s Designing with Microcontrollers (ECE 4760) Fall 2023 session designed a version of Simon Says on an RP2040 which they call Pico Says. It uses UDP packets over WiFi to communicate between the players, and supports VGA graphics for output. Each player’s hardware consists of a Pico W module plus a control panel containing the four LEDs and buttons ( red, green, yellow, and blue ) plus send and reset buttons.

For purposes of this lab, the modules were build on a solderless breadboard and used perfboard for the control panels. They weren’t entirely happy with their choice of UDP because they experienced frequent datagram dropouts in the noisy environment of the microcontroller lab. They also planned to implement sound effects, but ran out of time after spending too much time on the WiFi implementation, and had to drop that feature. In the end, however, they wrapped up their project and demonstrated a working game. We can only speculate whether this bonus lesson in resource management was intended by [Dr. Hunter Adams] or not.

Two ECE 4760 course references are highlighted in the write-up that helped them jump-start the project: the UDP and VGA examples for the Pico. These are good links to put in your RP2020 toolbox for future projects, in addition to the ECE 4760 course home page itself. We’ve covered several of these projects recently, as well as the curriculum switch from the Microchip PIC32MX-based Microstick II to the RP2040 last Spring.

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Gyro-Controlled Labyrinth Game Outputs To VGA

January 3, 2024 by Donald Papp 4 Comments

This gesture-controlled labyrinth game using two Raspberry Pi Pico units does a great job of demonstrating how it can sometimes take a lot of work to make something look simple.

To play, one tilts an MPU6050 inertial measurement unit (IMU) attached to one Pico to guide a square through a 2D maze, with the player working through multiple levels of difficulty. A second Pico takes care of displaying the game state on a VGA monitor, and together they work wirelessly to deliver a coherent experience with the right “feel”. This includes low latency, simulating friction appropriately, and more.

Taking a stream of raw sensor readings and turning them into control instructions over UDP in a way that feels intuitive while at the same time generating a VGA display signal has a lot of moving parts, software-wise. The project write-up has a considerable amount of detail on the architecture of the system, and the source code is available on GitHub for those who want a closer look.

We’ve seen gesture controls interfaced to physical marble mazes before, but two Raspberry Pi Picos doing it wirelessly with a VGA monitor for feedback is pretty neat. Watch it in action in the video, embedded just under the page break.

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Designing A Macintosh-to-VGA Adapter With An LM1881

October 7, 2023 by Maya Posch 3 Comments

Old-school Macintosh-to-VGA adapter. Just solve for X, set the right DIP switches and you’re golden.

If you’re the happy owner of a vintage Apple system like a 1989 Macintosh IIci you may know the pain of keeping working monitors around. Unless it’s a genuine Apple-approved CRT with the proprietary DA-15-based video connector, you are going to need at least an adapter studded with DIP switches to connect it to other monitors. Yet as [Steve] recently found out, the Macintosh’s rather selective use of video synchronization signals causes quite a headache when you try to hook up a range of VGA-equipped LCD monitors. A possible solution? Extracting the sync signal using a Texas Instruments LM1881 video sync separator chip.

Much of this trouble comes from the way that these old Apple systems output the analog video signal, which goes far beyond the physical differences of the DA-15 versus the standard DE-15 D-subminiature connectors. Whereas the VGA standard defines the RGB signals along with a VSYNC and HSYNC signal, the Apple version can generate HSYNC, VSYC, but also CSYNC (composite sync). Which sync signal is generated depends on what value the system reads on the three sense pins on the DA-15 connector, as a kind of crude monitor ID.

Theoretically this should be easy to adapt to, you might think, but the curveball Apple throws here is that for the monitor ID that outputs both VSYNC and HSYNC you are limited to a fixed resolution of 640 x 870, which is not the desired 640 x 480. The obvious solution is then to target the one monitor configuration with this output resolution, and extract the CSYNC (and sync-on-green) signal which it outputs, so that it can be fudged into a more VGA-like sync signal. Incidentally, it seems that [Steve]’s older Dell 2001FP LCD monitor does support sync-on-green and CSYNC, whereas newer LCD monitors no longer list this as a feature, which is why now more than a passive adapter is needed.

Although still a work-in-progress, so far [Steve] has managed to get an image on a number of these newer LCDs by using the LM1881 to extract CSYNC and obtain a VSYNC signal this way, while using the CSYNC as a sloppy HSYNC alternative. Other ICs also can generate an HSYNC signal from CSYNC, but those cost a bit more than the ~USD$3 LM1881.

An 8-bit ISA card with VGA, HDMI and composite video connectors

Upgraded Graphics Gremlin Adds HDMI Video To Vintage PCs

September 10, 2023 by Robin Kearey 34 Comments

Although new VGA-equipped monitors can still be bought, the old standard is definitely on its way out by now, being replaced by high-speed digital interfaces like HDMI and DisplayPort. It therefore makes sense to prepare for a VGA-less future, as [Yeo Kheng Meng] is doing. He designed an 8-bit ISA display card with an HDMI output that enables even the very first generation of PCs to talk to a modern monitor.

The design is based on the Graphics Gremlin by [Tube Time], which is an 8-bit ISA display card that aims to be software compatible with the obsolete MDA and CGA display formats while outputting a clean VGA signal. [Yeo Kheng Meng] modified the board by adding a TFP410 HDMI bus driver and replacing the rarely-used 9-pin RGBI connector with an HDMI version. He also updated the HDL code for the Lattice FPGA, which forms the heart of the graphics card, to account for the new digital output. While he was at it, he also added a few features he was missing in the original product, such as the option to select the color displayed in MDA mode and the ability to output both HDMI and composite video at the same time.

The video below shows the updated card in action in an IBM 5155 Portable PC. The HDMI port connects to a modern monitor, while the composite video output is routed to the 5155’s internal CRT as well as a small color monitor on top. The IBM thereby joins a small list of retro computers that have received an HDMI upgrade — the Amiga 500 and PlayStation 2 being other examples. HDMI might be a lot more complex to work with than VGA, but luckily there are open-source implementations that do much of the work for you.

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RGB Graphics On A DEC Rainbow With Reverse-Engineered Monitor

September 1, 2023 by Maya Posch 11 Comments

One of the delights of the boring pre-VGA era is that you get to express your creativity when it comes to making a random color CRT work with an equally exciting dual CPU computer like the DEC Rainbow 100. This is the situation that the folk over at Usagi Electric found themselves in with a recent project. The Rainbow 100 is an interesting computer in that it can boot not only DOS with its 8088 processor, but also CP/M on the Z80 processor. Although generally used in monochrome mode, it supports a color graphic card to output RGB signals via its male DB15 connector.

DEC Rainbow 100 to Princeton Ultrasync adapter. With strain-relief zip tie.

Unfortunately, the target monitor – a Princeton Ultrasync – featured a female DB25 connector that obviously wasn’t going to connect directly, thus requiring a spot of reverse engineering. Making this very easy, the PCB containing the input connector had the traces clearly marked with the intended signal, which just left the mapping of the two connectors. One complication here was with the Rainbow 100 outputting an RGB signal with sync-on-green, whereas the monitor expected a separate synchronization signal.

Fortunately, most analog monitors aren’t particularly fussy so long as they get the expected signal somewhere in the input, which just left the final issue, of the Rainbow 100 outputting the monochrome signal on a special monochrome pin. This allowed everything to work as it should, and leaving those of us who joined the computing era in the 90s appreciative of standard VGA cables, other than for those weird Sun and Apple systems with their proprietary connectors.

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