Bicycle back Safety Light

This is a circuit of bicycle back safety light. Feature : 13 LEDs flashing, 3V supply voltage, Simple circuitry, low voltage, high efficiency, battery powered. Component : Resistor, capacitor, LED, switch, battery, 7555 timer IC. [redcircuits.com]

Light Pollution Meter

This is a light pollution meter circuit. Feature : control range of about 2 to 30 microamps, Simple circuitry, easy to build, battery powered, 9V supply voltage. Component : LED, NPN transistor, Digital multimeter, Resistor, potentiometer, toggle switch, battery. [avery.home.mindspring.com]

Water-level Alert

The following circuit is a water level alert. Feature: Simple circuitry, low voltage, 1.5V supply voltage, portable unit, battery powered, low current consumption. Component : Resistor, capacitor, LED, 1N5819 diode, 7555 timer IC, piezo sounder, Battery. (redcircuits.com)

Water Level and TDS Sensor

This is a water level and TDS sensor circuit. Feature : Simple circuitry, Battery powered, 9V supply voltage, very low power consumption. Component : Resistor, capacitor, probe, battery, speaker, TLC555 timer IC, switch. [pbv.thunder-bay.on.ca]