Originally Posted by gunrunnerjohn:
He also has to provide 12VDC, so he'll need a rectifier and capacitor at a minimum.
Right.
The typical 555 timer IC chip (as used on that eBay relay module) only operates up to 16V DC. From the pictures of the Mini Commander it looks like they use triacs on its AC outputs. So the peak voltage outputs well exceed 16V. Even with a bridge/rectifier the capacitor will charge up above 16V DC and needs to be knocked down to 12V DC (or whatever) to safely operate the 555 chip.
In my hodge-podge of parts, one was a 12V regulator IC to address this very issue. I am an advocate of those eBay relay modules but, in this particular case, by the time you assemble the external components to make it compatible with the Mini Commander's 16VAC output, you minds as well build the 555 circuit and skip the relay.
And while using a 10 Amp relay (as on the eBay module) to switch a few milli-Amps of current to drive some LEDs, the relay coils used on those eBay modules draw a relatively large amount of current.