Comments on: Podcast #1: Introduction and Circuit Analysis

By: DrunkenUFOPilot

DrunkenUFOPilot — Fri, 20 Aug 2010 03:36:00 +0000

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!

By: No One

No One — Sat, 24 Jul 2010 02:30:53 +0000

Oh, and another thing you can use to illustrate circuits is this java app. Like this example of a Colpitt's Oscillator. http://www.falstad.com/circuit/e-colpitts.html

By: No One

No One — Sat, 24 Jul 2010 01:28:53 +0000

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.

By: chrisgammell

chrisgammell — Tue, 20 Jul 2010 01:30:16 +0000

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: ModernRonin

ModernRonin — Mon, 19 Jul 2010 22:17:08 +0000

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.