This circuit generates control signals for stepper motors. We found it in a 90s Popular Electronics. The power can be made with a 5 V supply so that it works as a shield.
This fast trigger circuit allows the counting of up to 300 pulses per minute. The circuit is from...
This intercom uses transistors from the 60s. It was found in a Japanese publication at the time....
This circuit is from an old publication from the 90s, but it can be adapted to operate with LEDs....