This 3-step circuit for generating digital signals was found in the November 1976 issue of Radio Electronics magazine. The maximum frequency depends on the flip flops.
We found this circuit in a Popular Electronics of the 90s. The circuit still uses light bulbs, but...
This circuit is from Linear Technology 2005 documentation. The circuit is based on company...
The integrated circuit used in this power supply is no longer very common in power supplies today....