In the last year, [Jeri Ellsworth] has been very busy. She was hired by Valve, started development of an augmented reality system, fired by Valve, and started a new company with [Rick Johnson] to bring her augmented reality glasses to the market. On the last Amp Hour podcast she spilled the beans on what went down at Valve, how her glasses work, and what her plans for the future are.
[Jeri] and [Rick]’s castAR glasses aren’t virtual reality glasses like the Oculus Rift or other virtual reality glasses that cut you off from the real world. The castAR glasses preserve your peripheral vision by projecting images and objects onto a gray retro-reflective mat and allows you to interact with a virtual environment with an electronic wand. So far, there are a few demos for the castAR system; a Jenga clone, and a game of battle chess called Team For Chess, a wonderful reference to Valve’s hat simulator.
The electronics inside the castAR glasses are fairly impressive; new frames are drawn on the retro-reflective surface at 100 Hz, positioning accuracy is in the sub-millimeter range, and thanks to [Jeri]’s clever engineering the entire system should be priced at about $200. Not too bad for an awesome device that can be used not only for D&D and Warhammer, but also for some very cool practical applications like visualizing engineering models of 3D prints before they’re printed.
Way back when [Ms Ellsworth] was a kid, she kept seeing the same circuit over and over again in her various op-amp books. It was a Wien bridge oscillator, a small circuit that outputs a sine wave with the help of a light bulb. Now that [Jeri] is much wiser, she decided to play around with this strange oscillator and found it’s actually pretty impressive for, you know, a light bulb.
The interesting portion of the Wien bridge is the gain portion of the circuit. It’s just a simple resistor divider, with a light bulb thrown in on one of its legs. When the current increases, this causes the light bulb to warm up (not enough to glow, though). When the temperature increases, the resistance in the light bulb increases, making the oscillator reach an equilibrium.
It’s a clever setup, but what about swapping out a resistor in place of the light bulb? In the video, [Jeri] tries just that, and it’s a mess. Where the light bulb circuit is amazingly stable with very, very low distortion, the resistor circuit looks like a disaster on the scope with harmonics everywhere.
A very cool build that would be perfect for an audio synth, but as [Jeri] says in her YouTube comments, “This doesn’t have enough distortion for indie bands.”
Continue reading “[Jeri] uses light bulbs in an oscillator”
[Jeri] has had a bear of a time moving up to Valve Software, but electron microscope is safely in her garage (!) and her electronics lab is slowly taking shape. Since she can’t bring out the real-life gravity gun she’s working on, she decided to show off a one-bit ADC that uses just a flip-flop to sample an analog waveform into digital data.
By toggling the clock input of a 74xx74 (or any flip-flop, really) and feeding the complimentary output to back into the data input, [Jeri] can get an output that is a 50% duty cycle feeding into the input of the chip. Adding an audio input to this data input with 10k pot to this feedback loop will cause the duty cycle to change in relation to the analog input, making a one-bit ADC.
As with any electronic shortcut, there are a few drawbacks: the clock cycle feeding into the flip-flop has to be pretty fast; at least a few dozen kilohertz if you’re sampling audio. Still, if you don’t have a free ADC pin, or you’d just like to build a bitcrushing guitar pedal, it’s a very simple (and cheap) way to get analog into a digital micro.
Continue reading “[Jeri] shows off a delta sigma ADC”
Here’s an interesting interview with [Jeri Ellsworth] over at the Jenessee Network. Usually the interviews I see popup with people are fairly short and sweet but this one really delves into many subjects and takes its time to explore. They start off talking about how [Jeri] began with hacking, which was literally smashing toys “with rocks” to see what was inside. They move on to discuss her adventures in building a race car, and then racing it as a teen… as an act of defiance.
In case you didn’t know, [Jeri] has been full time at Valve for about a year. Much of the discussion focuses on this from about 20 minutes in. She doesn’t hold back on information about what her daily life is like at valve as well as her experience during the hiring process. An interesting fact is that she didn’t initially recognize the name “Valve” and ignored them for a while. She does admit that if they had mentioned portal she would have paid a little more attention.
I was unaware that she had a side job putting the overflow of pinball machines she aquires into bars. When she moved to valve, she shut down that business, but she’s been flooding the halls with pinball machines, much to the enjoyment of the older folks.
[Jeri Ellsworth] finally set aside some time to talk about the build process for her Commodore 64 bass keytar. We think what started by taking a band saw to the guitar body ended up as a fantastic new instrument.
When she was showing off the project at Maker Faire we really only got a cursory look at what it could do. Her most recent video covers all that went into pulling off the project. Once the bulk of the guitar body was gone she tore the guts out of a dead c64 in order to mate the case with the guitar neck. Always the craftsman, she altered the computer’s badge to preserve the iconic look, then went to work adding pickups to each string using piezo sensors. This was done with Maker Faire in mind because magnetic pickups would have been unreliable around all of the tesla coils one might find at the event. These were amplified and filtered before being processed via an FPGA which connects to the original c64 SID 6581 chip.
Continue reading “[Jeri Ellsworth] on making her c64 bass keytar”
[Jeri] built this really cool C64 bass Keytar from a commodore64 and a cheap bass guitar. She’s using an FPGA to do the string detection and the key scanning, it then sends everything to the original 8bit sound chips. The reason that she is using a bass guitar is that the commodore sound chip only has 3 channels. There’s an interview with her from the maker faire, and if you keep watching, there are some other interesting projects too.
She notes that the implementation she went with has many performance issues due to the overtones the strings create when played. If she did it again, she’d go another route. Since [Jeri] has previously created the fully functional C64 games on FPGA, maybe she’ll add some video synth to this down the road.
We all need an excuse to play Half-Life 2 sometimes. [Jeri Ellsworth] put together a My First Crowbar controller to throw a few headcrabs across the room. It’s pretty much Half-Life 2 for the Wii.
The build is very simple – just a tilt switch hot glued to the underside of a childs-size crowbar. Two leads go from the tilt switch to the contacts on a (PS3?) controller. All you need to do to attack is swing the crowbar wildly.
[Jeri] has us wondering what other awesome game controllers could be made. Of course we’ve been wanting a real-life Gravity Gun or Portal Gun for years now, but right now we’re thinking about a real Katamari. We might need more hot glue.
As far as building our own, we’re thinking about using one of the Cheap DIY tilt switches we saw the other day. It’s a simple build, and sure looks like a lot of fun.
Continue reading “Pick up that can, [Jeri]”