CD4017B has the jitters

[Harald Kapp]

apart from the fact that there should be a reverse-biased diode (e.g a 1N4148) across the relay coil

Looks like the module has an 1N4007 as flyback diode:

A perfect fit, no additional diode required. Pin 2 of the 4017 can be connected directly to the input of the relay module (resistor and transistor are also on the module).
Unless @Bruce Ratcliffe wants to build the circuit from scratch acc. to the design in post #18. In this cas, I agree, the diode needs to be added.

BTW, here's a shot of the relay I'm using.

This is where you seem to have some of us confused. This we would not call a relay but a relay module. The relay is the blue plastic box only. The module also has a driver transistor and base resistor (Q2, R1):

And it has the flyback diode shown above (1N4007) plus an indicator LED


This module completely replaces this part of the schematic in post #18 with the addition of the flyback diode across teh relay coil which is missing in that schematic: