diff --git a/docs/space/electrical/README.md b/docs/space/electrical/README.md
index 029f3af..f0a5291 100644
--- a/docs/space/electrical/README.md
+++ b/docs/space/electrical/README.md
@@ -102,6 +102,21 @@ or if you want to see the internals:
 
 ![Swithbox open](pictures/switchbox_open.jpg "Opened up switchbox")
 
+#### Logic components
+
+There are currently 3 logic components installed for measurements and
+HomeAssistant related switching operations:
+
+* SM1: A [go-e Controller](https://go-e.com/en/products/go-e-controller) used
+  for measuring power consumption inside the space
+* A 32 Port Optocoupler board: Used to give Homeassistant hardware states
+* A 32 Output Relay Board: Used to let Homeassistant switch circuits on and off
+
+The optocoupler and relay boards are supplied with power from the power supply
+located near the top of the unit, which in turn received power from `1F8`.
+
+SM1 is powered via `3F8`.
+
 ### Light and schuko switching
 
 #### Light
@@ -155,4 +170,3 @@ to ease with maintenance works.
 ![TP2](pictures/its_term_2.svg "Terminal plan page 2")
 ![TP3](pictures/its_term_3.svg "Terminal plan page 3")
 ![TP4](pictures/its_term_4.svg "Terminal plan page 4")
-