Four-Hour Timer

The following schematic diagram is four hour timer circuit. Feature : easy to build, 3 hours 53 minutes total time,9V supply voltage. Component : 555 timer IC, Resistor, capacitor, switch, transformer, LED, CD4040B, Relay, BC547 transistor, 1N418 diode, variable resistor. [wiredworld.tripod.com]

DS1621 PC Thermometer Circuit

The following circuit is PC thermometer using DS1621. Feature : plug in any free PC com port, range of -20 to 125°C, Centigrade (°C) of Farenheit (°F) scale, basic accuracy and resolution 0.5°C, readable data log, sampling rate 1, 5, 30 or 60 seconds, basic accuracy and resolution 0.5°C, no external power supply required, easy to build, no calibration required. Component : 1N418 diode, Capacitor, LM2936Z, regulator, DB9 female, Zener diode, DS1621. [riccibitti.com]

CPU Clock Display Circuit

This is a CPU clock display circuit. This circuit shows the CPU speed. Feature : Simple circuitry, easy to build, 5V supply, can display CPU clock. Component : 7 Segment display, Resistor, 1N4001 diode, jumper. [turbokeu.com]