The purpose of this project was to create a useful yet easy to build Logic Analyzer that would provide much of the functionality of a real Logic Analyzer. The biggest drawback that the computer has is its sampling rate. The program was written on a 75 MHz Pentium computer which provided accurate sampling rates up to 10 kHz. Although this doesn’t match the speed of real Logic Analyzers, this should be sufficient speed to be useful for many projects. source

This little circuit will help you to scan the line of a 220V live wire in the wall. The FET gate is connected to a capacitive metal sensor (which is usually a simple metal plate). When you hold the sensor close to the wall, the LED will indicate the current flow around where it detects the wire. Works on 9VDC.source

The principle of the meter is very simple:You hookup a fully charged battery and load resistor to the meter, enter the value of the resistor and the cutoff voltage and start a discharge cycle. The meter will switch on the load using a power mosfet and continiously measure the battery voltage. To precisily measure the voltage a reference diode is used. During the discharge you can select to display the current voltage and current or the time expired and capacity so-far. If the cutoff voltage is reached the load will be disconnected and the capacity will be shown on the LCD display.source

With this mAh meter you can check the mAh capacitance of your NiCad or NiMH rechargeable batteries.when you insert a freshly charged battery, the LED will start blinking and the counter
will start counting. After some time (1-3 hours) the battery is discharged and the counter will stop. The readout of the counter indicates the capacitance of the battery in mAh.source

The circuit acts like a magnifying glass on part of the scale of an ordinary meter, namely the part of the scale we are interested in. For example, an ESV for testing a single NiCd cell would range from 1.17V at one end of the scale to 1.28V at the other end of the scale. With the full scale covering this narrow range, it’s easy to see voltage changes within the range.The circuit described here uses a bar graph display consisting of eight LEDs.source