Schematics / Instrumentation
2.4Ghz Spectrum Analyzer
Amazing design from Scott Armitage and Circuit Cellar Magazine:
"Forget dropping big bucks on a microwave spectrum analyzer. You can build your own for a fraction of the cost. Scott walks you through the process of building an ATmega48-based 2.4-GHz spectrum analyzer."...
Anemometer (Wind Speed Indicator)
In any wind generator installation, it's critical to be able to measure wind speed. That gives you a baseline against which to measure your machine's performance, and anemometers respond much more quickly to changes in windspeed than do wind generators....
Volume Unit Meter 
An audio volume-unit meter displays peak-related audio amplitudes to aid in accurately setting recording levels or for displaying an amplifier's operating conditions....
Build your own Gaussmeter
Have you ever wanted to find out how strong a magnet really was, or how the strength of the magnetic field varied as you changed the distance from the magnet or the temperature of the magnet, or how well a shield placed in front of the magnet worked? Voltmeters are fairly inexpensive and easy to find, but where do you purchase a Gaussmeter (also known as a magnetometer)....
Rainbow LED Voltmeter
Meters that indicate analog levels via a moving-pointer meter, a numeric display, or a column of LEDs typically occupy considerable panel area and require more than a casual glance to read. An indicator lamp or LED takes little space but indicates only an on or off condition. However, an unobtrusive LED that changes color as a function of a measured value would enable an observer to easily assess the measurement....
Precision Peak Detector
When you need a precision peak detector, you would usually implement it with one or several op amps and a few other associated components. This technique usually works well unless your design requires operation higher than a few kilohertz...
Capacitance Meter
This is a simple capacitance meter which can measure capacitance value easy. There are some measurement methods for capacitance, at one time the capacitance was measured with a impedance bridge or a dip meter...
Audible Circuit Tracer
This circuit tracer is a handy tool for finding connectivity paths on a pc board. Because the sense voltage you use to measure the path is lower than a transistor's VBE voltage, you can use the design...
Gravimeter
In Baker's apparatus, a small but powerful magnet delicately floats between two permanent magnets. A clever optical device senses small movements caused by gravitational shifts, seismic activity, thermal expansion, a stomping toddler and so on....
LoPIC Logic Probe with Pulser
This project is a combination Logic Probe and Logic Pulser. It is capable of testing all sorts of digital and microcomputer projects. You will find it extremely handy when designing a project as the golden rule is to...