@Ghanima: a final question:
if I duplicate the workable circuit to drive multiple relays, is it allowed to share Ground (X1-1) and 5V (X1-2) as depicted in my drawing.
Or should it be different separate circuits ?, however Ground and 5V will be shared via the PSU connectors then...
PS. what is OP stands for?
Unfortunately there are many different relay boards out there using this particular relay but that might feature different driving electronics. So it's difficult to give a definitive answer. There are however some indications that this excellent arcticle /1/ covers this board and the problems the OP describes.
(Image source: /1/)
I leave it to the OP to ...
From the rather unclear photos you have posted the device does not have an opto-isolator but a transistor.
It is unclear why it doesn't work, however there is another type of poor module, triggered by a low level, with a PNP transistor which is not controllable from 3.3V. (This saved the manufacturer some fraction of a cent.)
Without a circuit it is not ...
You've made a mistake, I'm afraid. You seem to be attempting to switch the relay coil with a GPIO pin. Unless your relay module is designed to use a 3.3V input you are at risk of breaking another RPi.
GPIO pins are for 3.3V - and ONLY 3.3V
In addition, the GPIO pins are delicate little flowers; they won't source (or sink) much current, and they don't ...
Most MOSFETs will not work with the RPi at all; the ones that do will not work well. Here are the issues:
Most MOSFETs require gate-source voltages (Vgs) that exceed the 3.3V output the GPIO is able to provide. These will not work at all.
The MOSFETs with Vgs ratings in the 3V range will suffer from one of the following:
They have very low power ratings, ...