updating

docs/electronics/Heated Bed.md

@@ -37,4 +37,13 @@ When connecting the heatbed in the 12V setting it is important that you connect
 ![Alu-Heatbed MK3 24v Setting](https://reprap.org/mediawiki/images/8/8b/Alu_24V_small.jpg)
 
 
+### Electronics Design: 
+-----
+* To power the bed, you should use a PC PSU or universal power supply that can output at least 10A @ 12V.
+You may be able to get universal laptop-PSUs with adjustable voltage for a range of [15-24V at 80-180W](https://reprap.org/wiki/Heated_Bed#Electronics_Design_.231).
+
+* The heating elements can be nichrome wire, power resistors for higher temperatures or ready-made, flat heating-pads for lower temperatures.
+* nichrome wire is cheaper and takes less space then power resistors.
+* [This design uses a simple analog control circuit and is easy and cheap to build (20$US for the electronics)](https://reprap.org/wiki/Heated_Bed#Electronics_Design_.232). 
+