I have a relay connected to pin 4 of a raspberry pi, maybe like this
   one [1]https://www.amazon.com/Kyoto-Electric-KF0602D-Solid-State/dp/B00
   B888WVC ?  Relays are a very basic electric component that most
   electrical people would know about.  They let you turn things on and
   off with a microchip.
   On the relay I have a noise generator.  It just outputs noise when
   powered.  I drive the pin with a 40hz square wave, using a gnuradio
   block.
   By setting the time raster block's column number to the period of the
   square wave I can visualise it.  This is something I've tried to do for
   years and only just managed to do!  The visualisation helps stabilise
   work when issues happen, letting you see what is going on under the
   hood.
   One next step for visualisation for me right now is to make an
   accumulation block that combines many signals into one: decimating them
   in the packet domain.  But right now my system ran out of space for
   some reason building gnuradio.  How did I build it before if cleaning
   and rebuilding it exhausts space?

References

   1. https://www.amazon.com/Kyoto-Electric-KF0602D-Solid-State/dp/B00B888WVC