Categories
Analog Electronics Podcast

Podcast #1: Introduction and Circuit Analysis

This is my first podcast ever!

Sure, it’s something different, but give it a listen and let me know what you think in the comments!

[display_podcast]

By Chris Gammell

Chris Gammell is an engineer who talks more than most other engineers. He also writes, makes videos and a couple podcasts. While analog electronics happen to be his primary interests, he also dablles in FPGAs and system level design.

10 replies on “Podcast #1: Introduction and Circuit Analysis”

Chris:

Two items that may be of interest to you and maybe your readers.

1) For an analog IC design web site, check out http://www.cmosedu.com. Jake Baker (Boise State Univ) is a great guy, an excellent teacher, and his CMOS design books match or exceed such classic texts as those by Gray&Meyer, Allen, and Grebene. A wealth of information from beginning level through advanced analog/mixed-signal CMOS design and layout.

2) On my web site – which you kindly pointed to in an earlier post – I have been attempting to translate my class notes from "Intro to Electronics" courses I've taught a few times to a series of web postings. The first few are up but I get the idea they're rather clumsily presented – it's not easy reaching a balance between a class presentation mostly intended to be verbal and a discussion of those lectures not intended to be a full textbook. A full semester class has about 45 lectures at about 45 minutes each … Any comments or suggestions would be most welcome.

Did you ever learn this little mnemonic? The Eagle flies over the Indian sitting by the Rock. The E(agle) goes on top with the I(ndian) and R(ock) side by side on the bottom. E stands for voltage, I for current, and R for resistance. To figure out how to calculate for one, just cover the letter. So if I wanted to figure out current, I'd cover the 'I'. What remains is E on top and R on the bottom, or voltage divided by resistance.

In talking about the water-flow model of electricity, you mentioned in passing that a cap is like a water tank. This is the standard analogy, but it’s always bugged me. After a couple of days I figured out why. A tank is usually hard-walled, and thus doesn’t really behave like a cap when you consider the voltage/water pressure aspect. A water tank would go from 0V/psi to many V/psi very quickly, due to its rigidity. But this is only correct for a very small cap. With a bigger cap, the voltage rises much more slowly.

Instead, I think a better analogy is a water balloon. Imagine a straight section of pipe with a water balloon attached. This is like a wire with a cap to ground. As the water flows, the psi remains low when the balloon is more empty. As the balloon fills up (which requires water flow, aka current) the voltage/psi slowly rises as the tension in the balloon increases. Eventually you hit the elastic limit of the balloon, the voltage/psi in the line and balloon become equal, and there’s no further flow disruption. Further, if the pressure/voltage in the line should fall, the water balloon may push some water/current back out in an attempt to keep the pressures/voltages equal.

The capacitance of the cap can be thought of as the size of the balloon. Big balloons take longer to fill up, and consequently take more water/current to change their back pressure/voltage.

Finally, the analogy can be extended to a cap in series by considering the cap as a two-chamber water balloon. Water into one chamber pushes water out of the other chamber. Water flow cannot go through, but pressure waves can, and do.

I think this is nicely intuitive and gives a good “feel” for how a cap works in a circuit. Much better than the tank analogy.

I kind of like the water balloon idea but the "pressure" thing isn't that big of a deal really. If you really want to wrap your head around it, have a "tank" with a pipe of water pouring in at the top. Have the outlet at the bottom so the pressure builds up from the bottom of the tank. In this way the flow of water (current) that comes into the tank (capacitor) builds up pressure (voltage). Either way, it's just a conceptual model so whatever works for you is fine.

By Post Author

If you want to draw and talk at the same time, why not use a screen capture program? Watch any of the "Khan Academy" videos to see how it works. It's low-tech, but it just works. Even better if you have a touchscreen or something, or just draw with the mouse. And for schematics, just record Eagle or something.

Nice job for a first podcast! I think visuals would be very helpful, but OTOH to have something to listen to while doing something else is finet too.

You brought up the topic of “ground” and what you say is important. So often, “ground” has nothing to do with the big ball of dirt and rock we stand on. Shielding, which goes along with grounding, is a vital concept in all areas of electronics. Spacecraft are a great example. Nasty stuff happens if the engineers don’t pay sufficient attention to these concepts. Shielding and grounding may not be as sexy as chip design or photonics or cutting edge whatever this year, but is *so* vital. A good understanding of shielding and what “ground” can really mean can lead to solving tough production problems and thereby becoming the company hero.

A good resource on grounding and shielding are the books by Ralph Morrison, and his website http://www.ralphmorrison.com/Ralph_Morrison/Welco…

The topic is worth a podcast in itself!

Hey Chris, the link doesn’t seem to be available for downloading/playing this podcast anymore… body-text-filter problem, maybe? Also, how do I find out where your subsequent podcasts are from this original series? I’m aware of The Amp Hour, but would like to listen these on my daily commute, too.

Cheers!

Comments are closed.