Justin describes how to build a DIY four part motor. It requires a battery, a wire, a screw, and a small disc magnet. The hardest part is getting the screw to hang from the battery.

The way this motor works (as shown below) is by creating a closed circuit, where the current actually flows through the magnet. When this happens, a magnetic force turns the magnet, which spins the screw.

He also posted a Google video of the motor in action. This project has always been great for procrastination or entertaining youngsters.

Function generators are a huge investment. Even the simplest ones start out at about $30-$40. The folks at E-DSP were short on loose change so they did a little research and programmed a simple sound card signal generator.

Unfortunately, their software signal generator can only generate two functions, a sine wave or a square wave. Don’t forget your sound card is limited to 16 bits and 24khz. Therefore its reproduction of sine waves is not exactly perfect. Square waves should be reproduced near perfectly, though.

Also note that most PCI based sound cards have a limit of 2V, but you can always amplify this signal.

This has really sparked my interest so you can expect a Linux software signal generator later today!

A few people have designed boolean logic devices using LEGO pneumatics… I had suspected that there would be a large number of logic devices using mechanic principals, but a search for mechanical logic devices didn’t get many hits.

He decided to take matters into his own hands and design mechanical LEGO logic gates. A clockwise rotation represents a binary “one” while a counter-clockwise rotation represents a binary “zero.” The AND gate seems to require less pieces than a NAND gate, contrary to transistor design.

Unfortunately, he failed to implement an XOR gate. I wonder if it would require a more complex mechanical design (contrary to its simple transistor layout.) Kudos to the first person who implements a 16-bit binary adder with a Manchester carry chain using LEGO! VLSI is not my strong point.

Electronic Design has a smart battery charger schematic using only a single transistor. This is interesting as similar circuits now contain simple integrated circuits. When the battery’s charge falls below a threshold voltage, it is automatically recharged to a preset voltage. Unfortunately, the circuit has a couple of major flaws.

1. The single silicon junction makes the circuit extremely sensitive to ambient temperature changes. In the comments, someone mentions 0.5V per 10° which sounds about right.
2. When the power supply is disconnected (through power outage or physical disconnection), the battery discharges through the resistors.

For portable devices, you can avoid the second flaw by building the circuit into an external charger. However, this is not possible with UPS’s or other homemade backup power supplies.

If you have ever wanted to build your own binary clock, then Building a binary clock is the best reference I have ever seen. The page lists complete schematics and explains their functionality in detail. In my opinion, it looks a lot geekier straight from the breadboard!

Don’t forget to check this diy binary clock out, too.

Recently, I’ve been scouring the web for a cheap power supply. Building my own was definitely a consideration, but I never considered ripping one straight from a computer. Even my rusty old 386dx can supply ±5V, ±12V, and GND.

My journey led me to eHow’s wiki page that describes how to convert an ATX power supply into a workbench power supply. The instructions are extremely thorough. Unfortunately there is no 3.3V tap, but you can figure out how to add that on your own!

There is a similar conversion that explains the engineering and need for a power resistor in greater detail. Basically, the “cheap” circuitry in the ATX supply requires some (significant) current in order to “turn on.”