Tones (from the DTMF) on the telephone line are detected by Ul. When a valid tone is received, pin 14 (D
AV) of Ul produces a positive pulse that is used to drive NAND gates U2A and U2B and then to latch binary data from Ul into Quad-D flip-flop U3 (Ul could be decoded into 16 bits, if required). The Q outputs of U3 drive optoisolators that control triacs TR1, TR2, and TR3. PS1 is a 6-V 150-mA dc adapter that operates from 120 Vac.