Found in Electronics now from the 90s, this circuit uses a sensor from the time, which is difficult to find today. The circuit activates a sonalert-type buzzer.
This circuit is from an article that teaches how to assemble it in the magazine Electronics Now...
This circuit is from the National Semiconductor CMOS manual of 1977. What this circuit does is to...
This passive mixer has a configuration that does not always lead to good results from the use of...