Kicad EDA - Design a Product

Kicad is an open source (GPL) software for the creation of electronic schematic diagrams and printed circuit board artwork.

KiCad EDA Software Suite

Designed and written by Jean-Pierre Charras, a researcher at LIS (Laboratoire des Images et des Signaux) and a teacher in IUT de Saint Martin d'Hères.(France), in the field of electrical engineering and image processing.

The electrical rules check (ERC) automatically verifies your schematic connections. It checks for output pin conflicts, missing drivers and unconnected pins.

KiCad comes bundled with a vast library of symbols, footprints, and matching 3D models. They are community maintained so they never stop improving.

Make professional PCB layouts with up to 32 copper layers. This modern tool will help you lay out your board faster. As you draw your track, it pushes forward traces that are in the way. If that is not possible, your track will be rerouted around obstacles.

KiCad consists of ..

• kicad - the project manager
• eeschema - the schematic editor.
• cvpcb - the footprint selector for components used in the circuit design.
• pcbnew - the PCB layout program.
• gerbview - the Gerber (photoplotter documents) viewer

Simple Water operated relay

This was done in my early days, i have upgraded it, it ought to work, reduce the number of transistors to make it less sensitive, also a lower value in place of 10M will reduce its sensitivity, use clamping diodes to protect.

BD139 is used to drive the relay as it has good Ic. So you can even use a low ohm relay. If a Relay resistance is high its quality is higher, its power consumption is less and it needs thinner wire SWG-AWG.



See more at Circuits with Discrete devices

T2 and T3 form a darlington pair which drives T1. LED1 shows that the water level has reached the top of tank and also that the Relay is energised. D1 a freewheeling diode. R3 10M ensures that the high gain input does not float, yet the low leakage current thru the water is not drawn away by the 10M. R2 limits base current in case water is saline.