Schematics / Building Blocks
Solving Switch Bounce Problems
No chaste unblemished logic signals these; a scope will show the contacts torturously bouncing before settling into a stable state....
Op Amp Building Blocks
Here are two PDF files from the National Semiconductor Web Site that contain good tutorials on the fundamentals of Op Amp circuits and some of the basic analog building blocks that they can provide. The first document was written by the guru of Operational Amplifiers Robert Widlar in 1968 while the 2nd one, written in 1969 is somewhat derivative....
Low Voltage Rail-to-Rail Sample and Hold
This low-power circuit will sample signals between 0 and five volts. Settling time is determined not only by R2 but also by the series resistance of the analog switch (about 30 ohms) and the settling time of the OP amps. Holding the sample input high for about 1usec should yield about 0.1% accuracy....
Digital Knobs
Use this circuit to implement those knobs you see on oscilloscopes, radios and other devices. Turning the knob clockwise generates a series of low-going pulses from the COUNT-UP output while turning counter-clockwise generates a series of low-going pulses from the COUNT-DOWN output....
FAST, High Energy Pulser
This circuit is designed to provide very fast, high current pulses into laser diodes and LEDs. It can be modified to drive ultrasonic transducers as well. The light pulses from the laser are typically used for range-finder applications as well as fluorescent excitation sources. Some blue LED's from Nichia will generate UV energy when overdriven with short, high-current pulses....
Droopless Peak Detector from Maxim Integrated Products 
This circuit, which uses a digital potentiometer (pot) and a comparator, features droopless operation that is not normally associated with peak detectors that have traditionally used rectifiers and sample-and-holds (S/H)....
Micropower Linear PWM
Pulse width modulators are a fundamental building block. Among other things, they are used for remote sensing, DC motor control, and switch-mode power supply controllers....