audio sensing

Color Organ

I have had many requests for this circuit. It was a very popular unit years ago. The basic idea of the project is to make different colored bulbs light at different frequencies of music. The circuit connects to the speaker outputs of your stereo or to the back of your speaker. The music passes through […]

Relay Switch Activated by Tone and Signal

The essence of the circuit is for the input of tone and signal to provide an activation for the relay switch. Relay – an electrically operated switch where the current flowing through the coil of the relay is creating a magnetic field which attracts a lever and changes the switch contacts, thereby making its state […]

Audio Power Meter

This simple circuit indicates the amount of power that goes to a loudspeaker. The dual-color LED shows green at an applied power level of about 1 watt. At 1.5 watts it glows orange and above 3 watts it is bright red. The circuit is connected in parallel with the loudspeaker connections and is powered from […]

Acoustic Sensor

This acoustic sensor was originally developed for an industrial application (monitoring a siren), but will also find many domestic applications. Note that the sensor is designed with safety of operation as the top priority: this means that if it fails then in the worst-case scenario it will not itself generate a false indication that a […]