This ingenious circuit was found in a 1990s Popular Electronics. The oscillator is a 555 and the keyer uses an optocoupler in the configuration shown.
This circuit generates signals from 50kHz to 10MHz, depending on the crystal used. The transistors can be...
The transistors in this circuit from a 1994 technical publication may be BC548 and the 12 V supply...
In the figure we have a simple logic level indicator for TTL circuits or powered by 5 V....