I don't completely understand your question, but you don't need Zener diodes to protect the Arduino or transistor controlling the relay. You need an ordinary diode, placed in parallel with the relay coil, to prevent inductive kick.Keep in mind that you should never try to draw more than 20 mA from the Arduino output. Most relay coils draw more, so almost all relay circuits require a transistor to amplify the current. http://www.electroschematics.com/8975/arduino-control-relay/
when it comes time for a mass production
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