The circuit shown is from the National Semiconductor Linear Applications Handbook of 1994. using ADC0808. The circuit can handle data from up to 4 transducers with an 8-bit output.
This circuit is from a Popular Electronics from the 90s. The integrated circuit admits equivalents...
This very interesting project was obtained in a 1980 publication. It consists of a device that is...
This circuit beeps when the sensor is triggered by the opening of the freezer door or other...