Rediscovering Vacuum Tubes, Part 1

Posted on 2012-07-30 by M. Eric Carr

A while back, I bought several 6J6 vacuum tubes (dual triodes with a common cathode) on eBay, thinking that it would be an interesting project to wire them up and make an amplifier or something from them.

A 6J6 dual-triode vacuum tube (click for larger.)

Vacuum tubes work via the “Edison effect,” also known as thermionic emission. A hot filament (or a negatively-charged plate heated by a filament) will emit electrons into a vacuum. The flow of electrons can be increased and directed by drawing them toward a positively-charged plate. This combination of filament, vacuum, and plate forms a vacuum diode (since electrons will readily flow from the cathode to the plate, but not the other way around.)

With the addition of a negatively-charged grid between the filament and plate, the flow of electrons can be regulated by a relatively small signal. This allows amplification of an electrical signal, and makes possible amplifiers, oscillators, and even digital logic.

There is a nonlinear relationship between grid voltage and plate current, though. Some investigation was called for. The 6J6 is a dual-triode device, with a heated cathode, two grids, and two plate anodes. The two sections can be connected electrically in parallel (the grids tied together and the plate sections tied together.) I decided to initially test it in this configuration. Varying the grid voltage while measuring the plate current, I came up with the following performance graph:

 

Plate current as a function of grid voltage, for a 6J6 at 50V plate voltage. (Click for larger.)

The anomaly at roughly 0.5V grid voltage bears further investigation. While decreasing the grid voltage systematically, the plate current seems to have jumped quickly from about 4.4mA to 5.9mA. My guess is that the increasing current in the tube caused the dynamics to somehow shift to another mode of operation. I suspect that slowly decreasing the grid voltage may uncover a hysteresis curve.

Perhaps this could even be used as a way to store a single bit of memory. If so, this has amazing, profound implications for the future of tube-based computing!

This post is dedicated to the memory of my grandfather, Millard C. Carr, who would have been 95 years old today. We miss you, Granddad.


Posted in Analog, Digital, Electronics, HOW-TO, Nostalgia, Power, Science | 4 Comments

Freestylin’

Posted on 2012-07-30 by M. Eric Carr

Just about the only thing better than a nice cold soda is a nice cold free soda. It’s even better when it’s a nice, cold, custom-selected, free soda from one of the new Coke Freestyle vending machines.

A Coke Freestyle machine. (Click for larger.)

But perhaps I should explain about the “free” part.

Since I worked an earlier-than-usual schedule today, I was able to make a Geek Pilgrimage to Moe’s Southwestern Grill in Suburban Station. I’m not usually one for authentic Tex-Mex (I’m sure it’s very good quality, but the spices would kill me). This particular Moe’s, though, had one of those new Coke Freestyle custom soda vending machines. I’d seen it through the store window while passing by after hours and had meant to try it. I researched it online and found that it custom-mixes each drink — not only from syrup, CO2 and water like normal soda fountains, but from an inkjet-printer-like assortment of dozens of flavors that it can mix in over a hundred combinations.

I stopped by Moe’s today and ordered a drink. When I got to the machine, though, most of the selections were grayed out — empty. This was unusual; I wouldn’t have been surprised if one or two were sold out, but it seemed that every good drink was out of stock.

This is the part where it pays to be a geek. I’d read about these machines online and found a video describing an Easter egg in the “Water” menu — a secret way to pull up the maintenance menu. I tried it, and it worked.

Surprisingly, the machine seemed to have enough syrup for Dr. Pepper, Coke, Barq’s, and several other good drinks. What it didn’t have, according to the supply screen, was “HFCS” (High Fructose Corn Syrup.) AHA. No sweet stuff == no way to make any of the good drinks!

The "secret" maintenance screen, showing a lack of HFCS. (Click for larger.)

The shift manager who was looking at the machine with me checked in the back, and said that it had a full box of HFCS. Apparently nobody had told the machine this, though. I poked around a bit more and found a resupply menu. A quick reset later, and the consumer menu was lit up correctly once again. The manager, grateful for the help, let me have my drink on the house. I’ve never enjoyed a Fanta Lime soda this much before. Maybe that’s because I’ve never had a Fanta Lime soda before.

It’s good to be a geek.

 

Posted in Current Events, Digital, Digital Citizenship, Reviews | 2 Comments

An Introduction to Programming: Lesson 00

Posted on 2012-07-27 by M. Eric Carr

Computer programming is increasingly becoming an essential skill in many professions. Computers are one of the most powerful and useful tools available to us, and the ability to use them to solve problems is an important one when working in any of the STEM (Science / Technology / Engineering / Math) disciplines.

More importantly, though, programming can be fun!

Here’s a quick introduction, presented as a series of lessons that will get you started writing programs for your own computer. I’ve chosen to use FreeBASIC as the programming environment for several reasons, including ease of use, versatility, and low cost (meaning, no cost). While languages like C are more widely used in industry, FreeBASIC lends itself quite well to a “C-like” style of programming. Transitioning to C or another similar language would be mostly a matter of learning different syntax.

To write and run a program, you’ll need to:

  • Download and install FreeBASIC;
  • Start up FreeBASIC
  • Write a simple program or two (which I’ll provide, for now); and
  • Click a button to compile and run the program.

Downloading and installing FreeBASIC:

  • Click here to download a copy of the FreeBASIC installer.
  • Once it’s downloaded, run it and click through the prompts. (The default choices are fine.)
  • That’s it! On to the next step…

Starting up FreeBASIC:

  • Double-click on the FBIDE icon on your desktop.
  • (I told you it was easy.)

Writing your first program:

  • The traditional first program is a “Hello, World” program — one that simply prints “Hello, World.”
  • Click on the “New” icon at the upper right corner of the FreeBASIC program window (or click on File, then New.)
  • Type in the following:
    print “Hello, World!”
    sleep 5000
  • Click File -> Save, and give your program a name.
  • Press F9 to compile your program (translate it into something your computer can understand) and run it.
  • A new window with the phrase “Hello, World” should appear for five seconds, then disappear.
  • Congratulations — you just wrote a computer program!

Getting it to do more

  • The “Hello, World” program is nice and all, but it’s not really a fitting task for a computer capable of billions of calculations per second.
  • Why not have the computer add up all of the numbers between one and one million? (Don’t worry — it won’t take long.)
  • Click File -> Close, then File -> New. (Working with computer programs is really just like working with documents in Word and similar programs.)
  • Enter the following text in the window. (We’ll cover what this means in later lessons.)
    dim as ulongint x, total
    total = 0
    print “Adding the numbers…”
    for x=1 to 1000000
    total = total + x
    next x
    print “The total is: “;total
    sleep 10000
  • Click File -> Save, give the program a name (maybe “number sum” or something), then press F9.
  • You should quickly get the answer: 500000500000.

The next lesson will cover how to get started writing your own BASIC programs.

 

Posted in Coding | Leave a comment

PIC startup debugging techniques

Posted on 2012-07-10 by M. Eric Carr

PIC microcontrollers are great little devices — reliable, fairly powerful, reasonably easy to use, generally available in DIP form factor, and very inexpensive. Sometimes, though, an overlooked configuration setting or a missed connection can cause a PIC-powered project to refuse to execute code.

Here is a generic version of the troubleshooting process that I usually go through (more or less in this order) if a PIC-based project doesn’t start up after having been programmed. Going through this checklist should cover most of the common problems that will keep a PIC from running. Double-check everything — even the “obvious” things like making sure power and ground are connected.

 

First, make a visual inspection of the circuit:

  • Is power connected to all Vcc pins?
  • Is Ground connected to all Vss pins?
  • Is this the correct type of PIC for your code?
  • Is the PIC seated correctly, especially if breadboarded?
  • Is the PIC in the correct orientation in the PCB or breadboard?
  • Are any of the PIC’s pins bent or otherwise not making contact?

 

Next, inspect the chip configuration in MPLab:

  • Is the correct type of PIC selected in MPLab?
  • Is the oscillator configuration set correctly?
  • Is the watchdog timer either disabled (or handled in code)?
  • Is the PWRON timer set? (This isn’t strictly necessary, but this helps ensure reliable startup)
  • Is the brownout reset configuration correctly set? (This may not be strictly necessary)

 

Check for correct programming procedure:

  • If connected to the programmer/debugger, is ~MCLR high?
  • Was the chip successfully programmed? (Check the output messages.)
  • Was it the correct program?

 

Next, look over the code for common mistakes:

  • Is the PIC actually executing code, but all TRIS registers are set to input?
  • Did you disable all unused peripherals which share the ports you’re using?
  • Did you enable all peripherals which you are using?
  • Are you using the correct definition file for this PIC?
  • Is your code going off into the weeds?
  • If your program reaches the end of the code, is this handled with a loop or a SLEEP instruction?
  • Is PCLATH set correctly when executing CALLs and GOTOs to other program pages?
  • Is PCLATH set correctly when returning from routines in other program pages?
  • Does your code execute a RETURN without a corresponding CALL?
  • Does your code execute too many (> 7) nested CALLs (including an infinite series of them)?

 

Next, inspect the signals and voltages at the chip pins:

  • Is the power at the correct voltage wrt Ground, on all power pins?
  • Is ~MCLR at Vcc (not floating, grounded, or at Vpp)?
  • Is the power clean? (try a decoupling cap or two near the PIC power inputs)
  • Using a ‘scope or at least a logic probe, check all inputs to the PIC (right where the pins enter the chip body). Are these signals what you would expect to see going into the chip?

 

Finally, try active debugging techniques:

  • Try another PIC (and remember to program it).
  • Try executing simpler code on the PIC.
  • Try disconnecting as many outputs as you can (shorted outputs could be causing a failure).
  • Try running a simple, known-good piece of code written for that same processor.

 

Posted in Assembly, Coding, Digital, Electronics, HOW-TO, PIC Microcontrollers | Tagged , , , | Leave a comment