This circuit generates the busy tone of ordinary telephones. The transistors can be the BC548 and the components of the T filter and the multivibrator can be changed to obtain the exact tone.
This circuit is from Motorola's Linear Interface ICs of 1993. The integrated circuit is not common...
The integrated circuit used in this 80's temperature control is not very common today. The load...
Found in a1968’s Burr Brown documentation, this shield uses an integrated circuit from that time,...