This interesting circuit found in American documentation generates a busy signal, without you having to take the phone off the hook if you do not want to answer. The components used are common.
This circuit was obtained in the 1977 RCA CMOS manual. The circuit has the frequencies determined by the...
We found this circuit in a 2004 documentation. The circuit consists of a standard lamp for testing...
Found in a Popular Electronics of the 90s this configuration can be seen elsewhere on our site....