USB adapter for an old VT100 keyboard


Ah, the VT100, the first dumb terminal that was controlled with a microprocessor. This ancient beast from the late 70s is quite unlike the terminals you’d find from even five years after its vintage – the keyboard connects via a TRS quarter-inch jack – the electronic and code design of this terminal is a bit weird. [Seth] was up to the challenge of making this mechanical keyboard work as a standard USB device, so he created his own USB adapter.

On the little quarter-inch to USB adapter, [Seth] included an HD 6402 UART to talk to the keyboard, along with a Teensy dev board and a few bits of circuits stolen from DEC engineers. The protocol between the keyboard and terminal is a little weird – first the terminal sets a bit in a status word, then the keyboard scans all the key rows and columns in sequence before telling the terminal it’s done. Yes, this gives the VT100 full n-key rollover, but it’s just weird compared to even an IBM Model M keyboard that’s just a few years younger.

[Seth] finally completed his circuit and wired it up on a perfboard. Everything works just as it should, although a little key remapping was done to keep this keyboard adapter useful for Mac and Windows computers. It’s a wonderful bit of kit, and any insight we can get into the old DEC engineers is a wonderful read in any event.

Vidias below.

Continue reading “USB adapter for an old VT100 keyboard”

Digital IR Theremin

Digital IR Theremin

This Digital IR Theremin creates tones based on the distance of an object from its IR sensor. There’s no microcontroller here, since the project is part of an Introduction to Digital Electronics course. Instead, it uses a handful of comparators, transistors, AND gates, and a 555 timer to make noise.

The comparators are connected to create window comparators. This configuration will output a digital 1 if the input is between two reference voltages, and 0 if it is not. Using this, the analog output of the IR range sensor can be converted to digital values.

The 555 timer takes care of creating the output waveform. A specific resistor is switched in to the timer’s RC circuit depending on which window comparator is active. This allows for a different tone to be played depending on the distance from the IR sensor.

The result is a square wave, which has a frequency dependant on how close an object is to the IR sensor. By selecting the right resistances for each distance, the theremin can be tuned to play a specific scale.

This is a neat project for people looking to learn digital electronics, and the write up does a great job of explaining the theory. After the break, check out a video of the theremin generating some tones.

Continue reading “Digital IR Theremin”

Increasing a digital servo motor’s range of motion

Unhappy with the 120 degree range of movement for this digital servo motor [Malte] set out to expand its flexibility. He settled upon a hack that alters the feedback potentiometer in order to give the motor a wider range (translated).

The test video (embedded after the break) shows tick marks for before and after his alterations. You can see that the wider tick marks get much closer to the 180 degree range he’s interested in. The control method is no different than it was before, the internal circuitry is still listening for a control signal with pulses between 1 and 2ms to establish the position of the servo horn. [Malte] added resistors on the two outside legs of the feedback potentiometer. This is what that control circuit measures in order to judge the position of the servo horn. He’s using 1.6k Ohm resistors in this demonstration. But he didn’t just drop them in willy-nilly. His writeup discusses the calculations he used to determine the target voltage for the motor position he wants.

Continue reading “Increasing a digital servo motor’s range of motion”

Intel’s new way of creating randomness from digital orderliness

Random number generation is a frequent topic of discussion in projects that involve encryption and security. Intel has just announced a new feature coming to many of their processors that affect random number generation.

The random number generator, which they call Bull Mountain, marks a departure from Intel’s traditional method of generating random number seeds from analog hardware. Bull Mountain relies on all-digital hardware, pitting two inverters against each other and letting thermal noise tip the hand in one direction or the other. The system is monitored at several steps along the way, tuning the hardware to ensure that the random digits are not falling more frequently in one direction or the other. Pairs of 256-bit sequences are then run through a mathematical process to further offset the chance of predictability, before they are then used as a pseudorandom number seed. Why go though all of this? Transitioning to an all-digital process makes it easier and cheaper to reduce the size of microchips.

A new instruction has been added to access this hardware module: RdRand. If it works as promised, this should remove the need for elaborate external hardware as a random number source.

[via Reddit]

chipKIT Sketch: Mini Polyphonic Sampling Synth

In our hands-on review of the Digilent chipKIT Uno32, we posed the question of what the lasting appeal might be for a 32-bit Arduino work-alike. We felt it needed some novel applications exploiting its special features…not just the same old Arduino sketches with MOAR BITS. After the fractal demo, we’ve hit upon something unique and fun…

Continue reading “chipKIT Sketch: Mini Polyphonic Sampling Synth”

Real-time digital puppetry


If it sometimes seems that there is only a finite amount of things you can do with your kids, have you ever considered making movies? We don’t mean taking home videos – we’re talking about making actual movies where your kids can orchestrate the action and be the indirect stars of the show.

Maker [Friedrich Kirchner] has been working on an application called MovieSandbox, which is an open-source realtime animation tool. A couple of years in the making, the project is cross-platform compatible on both Windows and Apple computers (with Linux in the works), making it accessible to just about everyone.

His most recent example of the software’s power is a simple digital puppet show, which is sure to please young and old alike. Using sock puppets fitted with special flex sensors, he is able to control his on-screen cartoon characters by simply moving his puppets’ “mouths”. An Arduino is used to pass the sensor data to his software, while also allowing him to dynamically switch camera angles with a series of buttons.

Obviously something like this requires a bit of configuration in advance, but given a bit of time we imagine it would be pretty easy to set up a digital puppet stage that will keep your kids happily occupied for hours on end.

Continue reading to see a quick video of his sock puppet theater in action.

[via Make]

Continue reading “Real-time digital puppetry”

Pidato box adds vibrato effect to digital pianos


[Joren] likes his digital piano, but it was missing one key component that he wanted to use: the ability to produce vibrato while playing. Vibrato can be done in several different ways on regular pianos, but it seemed as if there was not a lot of consideration given to the effect when designing digital pianos.

He enjoys playing all sorts of music, including solos from Franz Liszt which suggest using vibrato at times, so he decided to build himself a vibrato box. Constructed with a bit of assistance from the friendly folks at Hackerspace Ghent, his “Pidato” incorporates an Arduino and three-axis accelerometer to get the job done.

The Arduino is connected to both the MIDI output of the piano as well as to the accelerometer, which he has mounted on his wrist. While playing, all he needs to do is simply move his hand rapidly to produce the vibrato sound as you can see in the video below. The Arduino code filters out any other sorts of movements to ensure that he does not accidentally trigger the effect when it is not desired.

Check out the video below for a quick demonstration of the Pidato box.

Continue reading “Pidato box adds vibrato effect to digital pianos”