The circuit presented is based on the National Semiconductor's LM3524, a component not common today. The circuit is from the 1994 Linear Applications Handbook.
This circuit was obtained in an old documentation, but it is still current by the used components....
This circuit makes use of a transconductance operational amplifier. It generates signals with TTL...
This circuit is from a 90s Popular Electronics. The transistors are of general use and the buzzer...