IN-9 neon bargraph experiment #3: digital output control

Posted on 31 Dec 2011 04:28

My first thought about building a widget around the IN-9 was to use an opamp chip to process an input signal and a timer chip to regulate power. That was what I did for the magic eye VU meter project. Magic eye tubes have an interesting property in that they have a logarithmic response curve, so if you're thinking of making something like a VU meter, that simplifies the requirements for the input circuit. As I looked into such a design for the IN-9, I realized that I not only would I need to add the log scaling (not a big deal), but that I'd also have to add temperature compensation. The expanding requirements got me to wonder if it wouldn't be simpler, and possibly even cheaper to use a small microcontroller instead. Digital logic never needs temperature adjustment.

I pulled out my MSP430 kit and put together a basic circuit, and after a few hours of dicking around with that, I realized that while there are many neat things about the MSP430 family, they are best suited for low-power, low-voltage projects, and are poorly suited to this particular high-voltage project. I managed to kludge something together using voltage regulators and output transistors, but as the circuit got uglier I realized that this was an unsatisfying design direction. So I scrapped it and started over.

My next choice, which turned out to completely exceed my expectations, was to use an attiny85 (I could easily have done this with an attiny25, but the '85 is what I have on hand). Being a committed minimalist, I am delighted by the utter simplicity of this circuit:


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One could think of the modern democratic social contract thusly:

Posted on 13 Dec 2011 20:49

Even those who do not understand prisoner's dilemmas deserve to be protected from them, and everybody benefits when we do.

The reactionary mind rebels against this logic and believes that it will come out ahead in a unconstrained contest. In the overwhelming majority of cases, this belief is mistaken. That is because such a belief is most often based entirely upon emotional intuition and is thus impervious to reason. This is an essential problem of contemporary political economy.


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First working build of magic eye level meter

Posted on 11 Dec 2011 00:13

Now using sooper-kool EM800 tubes instead of frumpy old 6E2 tubes.

magic_eye_circuit.jpg

Circuit to the left of center is 555-based boost converter. Circuit to the right is LM358-based preamp.


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Blog tags: 555 6e2 em800 em84 em87 eye lm358 magic meter tube vu

You must squeeze, Rabban, *squeeeeeze*...

Posted on 07 Dec 2011 00:55

I coaxed another 20% speedup out of the spectrum analyzer for a 3fps gain. The radio module SPI interface is rated for 2MHz, but it turns out you can overclock it a bit, which I achieved by tweaking the OSCCAL register. I see that cringe, but hey, this is very far from a production design! The radio stabilization period is now the unambiguous limiting factor, which means it's unlikely to get any faster :(

Okay, I thought of two more possible ways to speed it up: 1) Switch to a different radio module that might be faster e.g. the TI CC2500. 2) Parallelize the sweep by adding a second radio module. That would complicate the algorithm, but I already know exactly how to do it.


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So many stupid glowy vacuum tubes, so little time

Posted on 02 Dec 2011 10:04

IN-9.jpg

The magic eye project is nearing completion. My little op amp preamp circuit works like a charm for driving the tube from line level. I have a couple of parts on order, but once everything arrives it should all come together very quickly.

So I ordered a batch of IN-9 neon bargraph indicators so I can iterate the design with yet another variety of obsolete communist vacuum tubes.


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The dark season means project time again

Posted on 27 Nov 2011 00:48

magic_eye.jpg

Most years I don't like to have too many indoor projects while the weather is good, thought last year I made an exception. In Seattle, prime project season is roughly November-April, and this year I'm kicking it off by finishing some of last year's unfinished (or underdeveloped) projects.

Right now, I'm finishing the magic eye stereo VU meter. Last year I left it just barely complete enough to demonstrate that the tubes work. That meant I got a half-baked power supply working (and then only badly), and I used an external amplifier to drive the audio inputs. This year, I reworked the power supply and I'm adding an internal amplifier so the unit is self-contained and driven by a line level signal. I'm very pleased with how it's turning out, and I think it's going to look stupendously awesome when it's done.

Earlier this month, I reworked the firmware the RF scanner. After living with it for a year or so, the slowness of the refresh rate bothered me and I thought I could do better. This turned out to be an exercise in chasing bottlenecks until I found an external limiting factor. It's not always obvious what the limiting factor will be. In this case it turned out to be close contest between the SPI speed of the radio module interface and the time delay needed for the radio to stabilize before sampling channel strength.

The result is quite satisfying. Refresh rate is now nearly 3x the speed of the old build:

I also plan to finish my IV-4 / IV-17 VFD tube clock, and I have a couple of other project ideas that might be promising. I might even do a straight-up software project for the first time in a while, to celebrate my new Android tablet.


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A Call for the Catevator

Posted on 02 Jul 2011 22:41

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My cat Wilma is a sweet old lady. She had her 18th birthday this spring, and while she is still as charming and lovable as ever, she is definitely beginning to show her years.

Anyone who has spent much time around cats knows that they are creatures of habit. And like all cats, Wilma spends most of her time lying around in one or two favorite spots. One of those spots is on my bed. Wilma has never been the most athletic cat, with a stocky build and short legs and a clumsiness at leaping which is unbecoming of her species. But even though my bed is pretty high off the floor, she likes it so much that she will jump up on it anyway, however ungracefully.

Wilma is a very social cat, and will often migrate to a room where there is human company. She doesn't expect much attention, but she does like to be near the action. Sometimes if she's alone in another room, she will cry until somebody comes to check on her. The moment she realizes she has company she will chirp, walk over to greet the inquirer, and follow that being to its destination.

Often at night, after I've gone to bed, Wilma will cry forgetfully from another room until I wake up and call for her. She will always respond by pushing the bedroom door open with her nose and standing by the side of the bed. Sometimes she will jump right up from there, and sometimes she will sit there and meow. In the old days, if she meowed, I'd call for her again and she'd jump up. Lately she'll keep meowing until I dangle my arm over the side of the bed for her to head butt. At this point, I might be able to convince her to jump up on the bed with the kind of great encouragement that is difficult to come by after being awoken by a cat in the middle of the night. More often than not, it's easier for everybody if I reach down and lift her over the side of the bed in a maneuver I've come to call "The Catevator."

You would think that a cat as simple as Wilma would settle into predictable behavior, but she has always had a way of inventing new quirks and tricks to surprise me. In spite of the late-night assistance, she still jumps up on the bed on her own during the day when I'm not in the bedroom. But today she caught me off guard with something new. I heard her crying in the bedroom, in the middle of the day. I walked in to find her standing by the side of the bed, looking up and meowing.

She was calling for the Catevator.


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My unsatisfactory grocery situation

Posted on 25 Jun 2011 01:04

I live in the city. Not the dense hi-rise-condo-city or even the row-house-city. But I do live in a medium-density, walkable neighborhood of small-lot craftsmen and bungalows with the occasional townhouse cluster or small apartment building. The neighborhood immediately to the east of me is somewhat denser and more obviously urban.

Now, I chose my home and this neighborhood purposely for these qualities of density and walkability. I have easy public transportation access to most of the rest of the city from here, and I live across the street from a Zipcar lot. I can walk to a couple of dozen restaurants and a dozen coffee shops.

Most importantly, I can walk to the grocery store, which I do every day. My neighborhood is big enough to support one supermarket, but apparently is not big enough to support two. So I can walk to the store, but within the constraints of my chosen circumstances, I have no real choice about it. This wouldn't be a problem if I liked the grocery store, but I don't. At all.

The things that I want in an urban neighborhood grocery store really don't seem that unreasonable to me, and yet they are hard to come by:

  1. I want the assortment to be carefully curated to fit the tastes of the local population. I do not want to see 57 different kinds of spaghetti sauce and 38 varieties of toothpaste. 10 kinds of pasta sauce seems like way more than enough variety if they are well-selected. Trader Joe's is a good example of what I mean by curation, though I understand that TJ's is terribly flawed in other regards and specifically in regard to my next point…
  2. I do not want to patronize any kind of national chain or franchise, of any variety whatsoever. I'm not saying that every single store has to be a mom-and-pop, but I am saying that there is no such thing as "too local."

The short of it? I fucking hate QFC and I fucking hate Kroger, but I'm stuck with them unless I move.


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