Lightning Detector
The following circuit is an improved version of my original Lightning Detector designed to run on a 5 volt supply. The new circuit features a superior RF section with a single resonance near 300kHz and plenty of sensitivity...

Simple pH Meter
Here's a circuit from the datasheet for the National Semiconductor LMC6001 ultra low input current amplifier. Scroll down to page 10 for a complete description of the circuit and the calibration procedures...

16-bit A/D Converter w/ RS232 Interface
A PC usually requires a plug-in ADC card to process analog signals. However, with this circuitry a PC can communicate with an 18-bit ADC through its serial port...

Wireless Weather Monitoring Station
The Wireless Weather Station is composed of a remote station and a base station. The remote station is solar-powered and wakes up...

Isolated, 12bit, 8 Channel, A/D Converter with PC Interface and 0.1% Accuracy
This circuit uses the parallel port on the PC to interface to a MAX147 12bit, 8 channel A/D converter. By using the National LM4040AIM-4.1 reference, an accuracy of 0.1% is obtained...

Inductance Meter
The Inductance Meter Adapter described in this article is a circuit that, when connected to a digital multimeter, lets you measure low-value inductances. This circuit from Poptronix is a low cost device that provides approximate Inductance measurements. And, since it's from Poptronix, a circuit board layout is included...

Time Domain Reflectometer
This circuit is from Tomi Engdahl's page. It describes a nifty little TDR that, when combined with a regular oscilloscope, can be used to find discontinuities on long runs of cables...

Frequency Counter
This is a project developed by Tom Napier for Circuit Cellar Inc. It's a good fundamental circuit based on a PSoC chip...

Reflectometer
Faults such as opens, shorts, or mismatches can be precisely located along the length of a cable by using a time-domain reflectometer. This device launches a rectangular pulse toward the cable's end and waits...

Inclinometer
An inclinometer (tilt-measuring circuit) whose sensor (SN1) is filled with liquid electrolyte. Acting as a potentiometer, the inclinometer produces a voltage proportional to tilt on its center electrode...