Having used M33G GPIO, I discovered that their digital output pins provide 3,3V, enough to drive a relais module.
Recently bought KNOT and KNOT Embedded LTE don't - they can still be used to switch relais when using external power for the relais.
With M33G and the KNOTs, I measured between the digital out and ground pin.
The question, what is the question?
No question, just wanted to share my observations. Digital output is not covered that much in the forum.
Yep, thanks 
, but if you have the time and suitable instruments, it would be good to know how much power is actually delivered, i.e. the max mA the "simple" relais can actually draw from that digital output.
There is a concrete risk of frying something on the board if too much power is absorbed or it is held powered for too long.
Hi, thanks for pointing me to the "simple" relais, which in fact is a solid state relais module (Fotek SSR-40DA - original post has been edited). I am using a 12V DC power supply, power supply + attached to the relais module's control input +, power supply - connected to Mikrotik ground pin, relais module control input - attached to Mikrotik GPIO. I doubt my garden-variety multimeter counts as "suitable instrument", but as a ballpark figure I measure ~10-100mA between relais module and Mikrotik GPIO... according to the documentation one should not exceed 0.5A @ 24V... so I'm pretty sure, I'm safe.
Ahh, good.
So you tested with a SSR module, the SSR-40DA sheet:
https://cdn.sparkfun.com/datasheets/Components/General/SSR40DA.pdf
talks of a "trigger current" of 7.5 mA @ 12V, so 0.09W, if it is "linear" it should be 0.09W/3.3V=30 mA or so, which seems low enough to me.