Found in a 1990s US publication, this alarm circuit detects when a light beam is interrupted. Optical resources may be used for the sensor and instead of the alarm a relay may be used.
This circuit allows the use of headphones and microphones with diverse characteristics in audio...
We found this circuit in the 1994 Linear Applications Handbook from National Semiconductor. The...
This circuit was found in Radio Electronics from the 90s. The transistor is for general use. The...