Adventures with Eagle

Thanks to my extremely encouraging dad, I’ve been building circuits since I was seven years old. Freehanding a breakout board with my trusty Weller is second nature. Growing up, I always had a Heathkit or  Radio Shack 200-in-1 kit lying around in various states of assembly and/or modification. I learned to read schematics, and got quite good at physical assembly.

But I somehow never quite made the leap to designing circuits from scratch. Computers (and also girls) were a lot more interesting to me than studying electronics design. Fast forward a couple of decades, and I’ve noticed that years of tweaking other people’s designs and building things from kits gotten me into some bad habits. I have finally reached a point where I want to make circuits that do novel things, and freehanding, while quick and dirty, is not always the best choice for building complex circuits. Especially when high voltages are involved.

So after months of putting it off, I bit the bullet and started digging into CadSoft Eagle. To get going quickly, I worked through Sparkfun’s Eagle tutorial. I must say that after a bit of a shaky start (warning: UI designed by EEs ahoy!) I’m really starting to enjoy it. Draw a schematic, link it to physical components, make your connections, and you’re building real “grown-up” circuit boards! After about a weekend’s worth of effort, I’ve made a header board for the Nixie Tube HV Volt Meter project and a new revision of the Singing Arc. These are two-layer, through-hole boards with many more connections than are practical to run by hand.

Of course I’m excited now, because my designs look perfect (to my biased and poorly schooled eye) and they aren’t yet baked into copper and fiberglass. The real fun (and likely disappointment) will come in a couple of weeks when I get to populate, power up, and debug the boards. I know I still have a lot to learn ahead of me. But this free tool is becoming addictive. Playing the Eagle video game is a lot more fun than most. Sure there’s a lot of grind in the beginning, but by the end you level-up with real electronics…

I’m going to post my designs once I get the boards back, so I can give a full report on my first PCB attempt. Keep your fingers crossed!

Gigantic resistors

I ordered some 1000 Megohm resistors today. They’ll be the basis for some new HV measuring tools. I’m finding that I could really use a high voltage voltmeter and oscilloscope lately. Using a gigohm resistor (just like we use for the quarter shrinker) I can make a voltage divider, which will let me use my regular bench tools for testing. It looks like these will be good through 40kV, which will let me measure the performance of the pole pig! The ultimate plan is to make a voltmeter with a nixie tube display.

Why does all of the best HV stuff come from Russia anyway?

Arc speaker

I made a basic singing arc, based on this Instructable.

It uses a TL494 to switch a MOSFET very rapidly, dumping current into the primary coil of a TV flyback. The air rapidly heats up when the spark is on, and it cools quickly when switched off. This causes the air to vibrate, making sound just like a speaker.

I used a Hitachi flyback (about $10 on eBay) but any flyback with an open primary will work. You can use jumper clips for electrodes (as above), but they will melt eventually. Tungsten electrodes are much better. You can also use anything else that is conductive and will tolerate heat, such as chunks of pyrolytic carbon.

Here is Plasmana’s original schematic. Replacing the IRF540 with a bigger MOSFET (such as the FQA16N50) will let you dump more current at higher voltage across the flyback, making even bigger sparks. Adding a gate driver between the TL494 and the MOSFET would also likely help.

Plasma speaker schematic by Plasmana

A good heat sink is critical to keep the MOSFET from melting. I used a large copper CPU cooler with an integrated fan.