A few problems with that post #19 circuit :-
1) Standard TTL outputs can source only a couple of mA, so U3 will not be able to drive much base current through Q1.
2) Q1 may have a DC current gain as low as 25, so would need several mA base current to give enough collector current to energise the relay.
3) There is no catch diode across the relay coil, so the back-emf pulse when (if) the relay switches off could kill Q1.
1) Standard TTL outputs can source only a couple of mA, so U3 will not be able to drive much base current through Q1.
2) Q1 may have a DC current gain as low as 25, so would need several mA base current to give enough collector current to energise the relay.
3) There is no catch diode across the relay coil, so the back-emf pulse when (if) the relay switches off could kill Q1.