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 was obtained from an American 80's documentation. The balanced mixer can be shown in...
The LM143 is a high voltage operational amplifier not very easy to obtain today. The transistors used are...
This circuit found in old documentation is based on the 709 which is an operational amplifier that...