Saturday, February 28, 2009

Feedback Machine + Reading Magnetic fields

Allen was the brains behind this. We used this schematic and he added in an LED and a rheostat to control gain.

Because it has a magnet in it, the speaker conveniently sticks to the altoids tin while still being detachable. The indicator LED is inside (the red dot on the right).

The point of building this pocket amplifier was to listen to the output of a coil of thin gauge wire--ie, read magnetic fields. However, we built it kind of messily and it turned out to be more of a feedback machine. I did get some interesting results though, especially when holding it up to chargers and then unplugging them.

Later on, I found the following bit of treasure in a dumpster near the old Lucas building. It is a piece of old recording equipment, basically a magnetic tape reader attached to a 1/4" audio plug. I plugged it into my real amplifier, and achieved my original goal with much less extra noise.

I imagine it as a stethoscope for my computer.

Sunday, February 22, 2009

Solar Powered iPod Redux

Here is an older project of mine to set this blog in motion.

Summary of parts:
I am using the little printed circuit board that came with the garden light that came with the solar panel. It does what I need and was easy to hook up so I haven't bothered diagramming it. If I was a more dedicated person, I'd figure out the layout and share it online. But, I am not!

New iPods are more finicky than old iPods! Older iPods only need the input and the ground (+ and -, red and black, whatever). Many (storebought or homemade) cheap/old chargers work like this. They won't charge your new iPods though! New iPods (like my 80GB Classic) need their data lines hooked up too (the green and white ones if your cable is colored according to standards). Follow this diagram (which I found here).

Technically, I am supposed to use a 5v regulator (like the 7805). But when I hooked it up, I was only getting like 4.18v to my iPod across the + and - terminals. I took it out and I'm getting 5.09v (.09 too many) but I don't think my iPod is hurting too badly.

Other notes:
Rechargeable (as opposed to regular) AA batteries are 1.2v, not 1.5v. Four of those arranged in series supposedly make 4.8v, but I get 5.09 volts out for some reason. Works for me though!

Anyway guys I think this is pretty sweet! Sunlight streams into my device and at the other end I hear music.

Epilogue: Later, while attempting to add an LED to the mix, two wires touched and I shorted something on the circuit board by mistake, having once again forgotten to remove the batteries before soldering. I believe it was either the PNP or NPN transistor...but when I looked into replacing them I realized the circuit board had taken too much abuse already, and was falling apart. I plan to figure out (or find somebody who can figure out) how it worked and build a replacement someday.