DIY Fresnel reflector

Just like destroying an ant colony with a magnifying glass, there’s nothing like cooking hot dogs and roasting marshmallows with a nice parabolic reflector. Of course covering an old satellite dish with mylar or aluminum tape doesn’t take much skill, however cool it is. [Uwe] came up with a much more technical means of building a Fresnel reflector that will cook your hot dogs in seconds, but only on sunny days.

[Uwe] channeled a little bit of [Apollonius] when he realized that a flat cardboard ring with a section removed could be joined together into a conic section. The resulting section looks just like one concentric ring in a Fresnel reflector. [Uwe] wrote a small program in Visual Basic to calculate the necessary diameter and angle of his conic sections.

A bit of cardboard was cut out and pieced together with some very reflective aluminum tape. The resulting Fresnel reflector concentrates 117 times the normal solar radiation onto a small point. It’s more than enough to burn holes in construction paper, but we’ll be using a microwave for our lunch today.

Got Dead Bugs In Your Stereo?

It happens to the best of designers, spending untold amounts of time designing a complex device just to find out that you missed a trace, or you couldn’t rout something to something else. As time marches on its becoming a bit less common to pop open a commercially produced device and see a little jumper wire or 2 flying across a pcb, or a resistor straddling an IC.

But when [Ilektron] opened up a Yamaha Dolby Pro Logic receiver to scavenge for parts he saw a very big “oops” and a even wilder fix. The maker took a pair of relays, flipped them “belly up” and hot glued them into place on top of a pair of ICs. Then the mess was “dead bug” wired to the circuit using insulated and uninsulated bus wire, contacts were then reinforced / insulated using more hot glue.

This is one of the most hacky fix we have seen in a commercially produced product, but we would love to hear your amusing horror stories of “WTH did they do?” So join us in the comments after the break.

Programming AVR I2C Interface

I2C as many of you know, is a simple serial interface for many peripheral devices to micro controllers, but it can quickly become confusing to people who may not be accustom to it. Because of that, I2C tutorials are always welcome, and this new tutorial by [Embedds] does an excellent job of how to use I2C with an AVR with a 24C16 2Kbyte EEPROM.

The first half of the tutorial provides a clear explanation of how I2C works, including its signal structure, addressing, and data packets. It then moves on to AVR territory showing how to setup the I2C in an AtMega micro controller. The author uses a pretty standard to most of us Arduino, with software written in AVR C and a nifty little GUI programming application which eases the hassle of dealing with AVRDude directly.

Plenty of code samples follow from twiddling registers to a full blown application reading and writing bits from the EEPROM to a serial terminal on a PC.