This timer was found in a 1980 publication. With the BC548 for Q1, an 8-ohm speaker with 6 V power can be used. For 9 and 12 V the BD135 must be used and the speaker can be a common 8-ohm. The time is set in RV1 and depends on C1 which can be changed in the range of 100uF to 1000uF.
