Found in Fairchild documentation from the 90s, this circuit generates signals with the characteristics given next to the diagram. The power supply must be symmetrical.
Found in a 90s Popular Electronics, this circuit checks if a remote-control transmitter is...
This relay circuit with a dual channel MOSFET (not very common today) was found in an old American...
This application is not modern since few computers have parallel ports. But you can use this...