Current Corrected Af Amplifier The majority of modern AF power amplifiers drive the loudspeaker(s) with a voltage that is simply a fixed factor greater than the input voltage. It is fairly evident, therefore, that the power delivered by such amplifiers is inversely proportional to the loudspeaker impedance, since the cone displacement of a loudspeaker is […]
4 Way Traffic Lights This circuit produces traffic lights for a “4-way” intersection. The seemingly complex wiring to illuminate the lights is shown to be very simple.
Fan on off Control This circuit ( fan on off control ) lets you turn on/off a fan by just directing torchlight or other light toward its light-dependent resistor (LDR). The circuit is powered from a 5V power supply. Preset VR1 and a light-dependent resistor (LDR) work as the potential divider. Normally, the LDR’s resistance […]
Dancing Light – 555 circuits Here is a simple dancing light circuit based on NE555 (IC1) & CD4017 (IC2) . The IC1 is wired as an astable multivibrator to provide the clock pulses for the CD4017. For each clock pulse receiving at the clock input (pin14) of IC CD4017, the outputs Q0 to Q9 (refer […]
555 Circuits – Light Detector This circuit detects light falling on the Photo-cell (Light Dependent Resistor) to turn on the 555 and create a tone that is delivered to the speaker. Pin 4 must be held below 0.7v to turn the 555 off. Any voltage above 0.7v will activate the circuit. The adjustable sensitivity control […]
555 Circuits – Amplifier The 555 can be used as an amplifier. It operates very similar to pulse-width modulation. The component values cause the 555 to oscillate at approx 66kHz and the speaker does not respond to this high frequency. Instead it responds to the average CD value of the modulated output and demonstrates the concept of pulse-width modulation. The […]
METAL DETECTOR This circuit detects metal and also magnets. When a magnet is brought close to the 10mH choke, the output frequency changes.
Dark Light Activated Relay None of the parts are critical and easy available. The potmeter adjust the trigger ‘on’ level. The diode in the diagram shows to be 1N914. This is ok if you have a light-duty relay, also the 1N914 is a signal diode so actually does not qualify. Use a 1N4001 (or better) […]
Automatic Fan Switch The op-amp used is a readily available LM339. This IC contains four op-amps but we use only two of them. Use the others for spare or do something else with it. For the thermistor I used a small, very expensive ($52), glass-encapsulated type because I had it laying around but almost any […]
Heat Sensor, Automatic temperature control The Thermistor, or NTC (Negative Temperature Coefficient) of 10K, is a standard type. Most types will work. The one in the diagram is a 10K model made by Fenwal . The resistance lowers as the surrounding temperature increases which affects the output (pin 6) and energizes the small relay and […]
Alternating ON-OFF Switch Use this circuit instead of a standard on-off switch. Switching is very gentle. Connect unused input pins to an appropriate logic level (I used ground). IC1, the MC14069 (or 4069) is a regular Hex-inverter type and is constructed with MOS P-channel and N-channel enhancement mode devices in a single monolithic structure. […]
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