Video FPGA with No External A/D

You have an old PC with a nonstandard RGB video out and you need to bring it to a modern PAL TV set. That’s the problem [svofski] had, so he decided to use an Altera-based DE1 board to do the conversion. Normally, you’d expect reading an RGB video signal would take an analog to digital converter, which is not typically present on an FPGA. Instead of adding an external device, [svofski] used a trick to hijack the FPGA’s LVDS receivers and use them as comparators.

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Upgrading an Old Camera with a New Light Meter

[Marc] has an old Voigtländer Vito CLR film camera. The camera originally came with an analog light meter built-in. The meter consisted of a type of solar panel hooked up to a coil and a needle. As more light reached the solar panel, the coil became energized more and more, which moved the needle farther and farther. It was a simple way of doing things, but it has a down side. The photo panels stop working over time. That’s why [Marc] decided to build a custom light meter using newer technology.

[Marc] had to work within the confines of the tiny space inside of the camera. He chose to use a LM3914 bar display driver IC as the primary component. This chip can sense an input voltage against a reference voltage and then display the result by illuminating a single LED from a row of ten LEDs.

[Marc] used a photo cell from an old calculator to detect the ambient light. This acts as a current source, but he needed a voltage source. He designed a transimpedence amplifier into his circuit to convert the current into a voltage. The circuit is powered with two 3V coil cell batteries, regulated to 5V. The 5V acts as his reference voltage for the display driver. With that in mind, [Marc] had to amplify this signal further.

It didn’t end there, though. [Marc] discovered that when sampling natural light, the system worked as intended. When he sampled light from incandescent light bulbs, he did not get the expected output. This turned out to be caused by the fact that incandescent lights flicker at a rate of 50/60 Hz. His sensor was picking this up and the sinusoidal output was causing problems in his circuit. He remedied this by adding two filtering capacitors.

The whole circuit fits on a tiny PCB that slides right into position where the original light meter used to be. It’s impressive how perfectly it fits considering everything that is happening in this circuit.

[Thanks Mojay]

Hackaday Links: March 8, 2015

Nintendo is well known for… odd… hardware integration, but this video takes it to a new level. It’s a Gamecube playing Zelda: Four Swords Adventure, a game that can use a Game Boy Advance as a controller. [fibbef] is taking it further by using the Gamecube Game Boy Advance player to play the game, and using another GBA to control the second Gamecube. There’s also a GBA TV tuner, making this entire setup a Gamecube game played across two Gamecubes, controlled with a Game Boy Advance and displayed on a GBA with a TV tuner. The mind reels.

TI just released a great resource for analog design. It’s the Analog Engineer’s Pocket Reference, free for download, if you can navigate TI’s site. There are print copies of this book – I picked one up at Electronica – and it’s a great benchtop reference.

A few months ago, a life-size elephant (baby elephants are pretty small…) was 3D printed at the Amsterdam airport. A model of the elephant was broken up into columns about two meters tall. How did they print something two meters tall? With this add-on for a Ultimaker. It flips an Ultimaker upside down, giving the printer unlimited build height. The guy behind this – [Joris van Tubergen] – is crazy creative.

And you thought TV was bad now. Here’s the pitch: take a show like Storage Wars or American Pickers – you know, the shows that have people go around, lowball collectors, and sell stuff on the Internet – and put a “Tech” spin on it. This is happening. That’s a post from a casting producer on the classic cmp message boards. Here’s the vintage computer forums reaction. To refresh your memory, this is what happens when you get ‘tech’ on Storage Wars. Other examples from Storage Wars that include vastly overpriced video terminals cannot be found on YouTube. Here’s a reminder: just because it’s listed on eBay for $1000 doesn’t mean it’ll sell on eBay for $1000.

How Green Screen Worked Before Computers

If you know anything about how films are made then you have probably heard about the “green screen” before. The technique is also known as chroma key compositing, and it’s generally used to merge two images or videos together based on color hues. Usually you see an actor filmed in front of a green background. Using video editing software, the editor can then replace that specific green color with another video clip. This makes it look like the actor is in a completely different environment.

It’s no surprise that with computers, this is a very simple task. Any basic video editing software will include a chroma key function, but have you ever wondered how this was accomplished before computers made it so simple? [Tom Scott] posted a video to explain exactly that.

In the early days of film, the studio could film the actor against an entirely black background. Then, they would copy the film over and over using higher and higher contrasts until they end up with a black background, and a white silhouette of the actor. This film could be used as a matte. Working with an optical printer, the studio could then perform a double exposure to combine film of a background with the film of the actor. You can imagine that this was a much more cumbersome process than making a few mouse clicks.

For the green screen effect, studios could actually use specialized optical filters. They could apply one filter that would ignore a specific wavelength of the color green. Then they could film the actor using that filter. The resulting matte could then be combined with the footage of the actor and the background film using the optical printer. It’s very similar to the older style with the black background.

Electronic analog video has some other interesting tricks to perform the same basic effect. [Tom] explains that the analog signal contained information about the various colors that needed to be displayed on the screen. Electronic circuits were built that could watch for a specific color (green) and replace the signal with one from the background video. Studios even went so far as to record both the actor and a model simultaneously, using two cameras that were mechanically linked together to make the same movements. The signals could then be run through this special circuit and the combined image recorded all simultaneously.

There are a few other examples in the video, and the effects that [Tom] uses to describe these old techniques go a long way to help understand the concepts. It’s crazy to think of how complicated this process can be, when nowadays we can do it in minutes with the computers we already have in our homes. Continue reading “How Green Screen Worked Before Computers”

Logic Noise: Sweet, Sweet Oscillator Sounds

Welcome to part one of a series taking you down the rabbit hole of DIY electronic synthesizers based on (largely) CMOS logic chips. Instead of synths being commodity gear made by large corporate enterprises, we’ll be building with the cheapest available parts, using and misusing digital logic. In short, don’t expect pre-packaged smooth tones, because we’ll be making creative noise machines.

If you’re the chiptunes type, you’ll probably find something you like here. If you’re the circuit bender or electro-noise-punk type, this is gonna be right up your alley. If you just like to see CMOS chips wriggle and squirm in unintended ways, feel free to look over my shoulder. If you’re the type who insists that a screwdriver can’t be used to pry open a paint can, then maybe you’d better move along. There’s a thin line between the glitch as bug and the glitch as interesting discovery, and we’ll be dancing all over it.

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Annoy Your Enemies with the Hassler Circuit

[Craig] recently built himself a version of the “hassler” circuit as a sort of homage to Bob Widlar. If you haven’t heard of Bob Widlar, he was a key person involved in making analog IC’s a reality. We’ve actually covered the topic in-depth in the past. The hassler circuit is a simple but ingenious office prank. The idea is that the circuit emits a very high frequency tone, but only when the noise level in the room reaches a certain threshold. If your coworkers become too noisy, they will suddenly notice a ringing in their ears. When they stop talking to identify the source, the noise goes away. The desired result is to get your coworkers to shut the hell up.

[Craig] couldn’t find any published schematics for the original circuit, but he managed to build his own version with discrete components and IC’s. Sound first enters the circuit via a small electret microphone. The signal is then amplified, half-wave rectified, and run through a low pass filter. The gain from the microphone is configurable via a trim pot. A capacitor converts the output into a flat DC voltage.

The signal then gets passed to a relaxation oscillator circuit. This circuit creates a signal whose output duty cycle is dependent on the input voltage. The higher the input voltage, the longer the duty cycle, and the lower the frequency. The resulting signal is sent to a small speaker for output. The speaker is also controlled by a Schmitt trigger. This prevents the speaker from being powered until the voltage reaches a certain threshold, thus saving energy. The whole circuit is soldered together dead bug style and mounted to a copper clad board.

When the room is quiet, the input voltage is low. The output frequency is high enough that it is out of the range of human hearing. As the room slowly gets louder, the voltage increases and the output frequency lowers. Eventually it reaches the outer limits of human hearing and people in the room take notice. The video below walks step by step through the circuit. Continue reading “Annoy Your Enemies with the Hassler Circuit”

Universal Active Filters: Part 2

An easy way to conceptualize active filters is thinking about audio speakers. A speaker crossover has a low-pass, high-pass and band-pass effect breaking a signal into three components based upon frequency. In the previous part of this series I took that idea and applied it to a Universal Active Filter built with a single chip opamp based chip known as the UAF-42. By the way, it’s pretty much an older expensive chip, just one I picked out for demonstration.

Using a dual-ganged potentiometer, I was able to adjust the point at which frequencies are allowed to pass or be rejected. We could display this behavior by sweeping the circuit with my sweep frequency function generator which rapidly changes the frequency from low to high while we watch what can get through the filter.

In this installment I’ll test the theory that filtering out the harmonics which make up a square wave results in a predictable degradation of the waveform until at last it is a sine wave. This sine wave occurs at the fundamental frequency of the original square wave. Here’s the video but stick with me after the break to walk through each concept covered.

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