I am totally new to arduino and electronics, so excuse my dumb questions. I have tried to lookup what is unclear to me, but haven't found the answer.
I have an arduino pro mini working at 5V which I want to connect to a HC-05-Bluetooth-Modul working at 3.3V.
I googled and have learned I need a voltage divider or level shifter. I have found http://www.instructables.com/id/Level-Shifting-Between-TTL-and-CMOS/step4/Using-a-Zener-Diode/ which introduced me to the several possibillities and another site I have lost, which told me resistors do not work as cleanly as a zener diode (which is not totally true). So I bought a few of the parts mentioned at instructables.
The main question I have is: I have built what nevdull shows using my breadboard with a 3.3V zener diode and a 10K resistor using a smartphone 5V 1A as input voltage. I expected 3.18V output as shown at the example but got 2.08V. This was surprising me. Can you tell me why?
I have very few electronic parts because I am a beginner. I have changed the resistor with the smallest I have (1K74) and this gives me 3.08V output, so I believe that resistors reduce the voltage which leads to the different output voltages I have noticed. But how does it come that the same built works different here at my home compared to the example of nevdull?
Using no resistor kills the diode which might be a result of the diode is built for 500mA, so full 1A is too much for it, right? So, if I get a 3.3V zener diode at 1A I am good and don't need any resistor at all, is this correct?
You need to provide 3.3V power to the Bluetooth module and a Zener diode + resistor combination is fine for that, as long as the components are chosen correctly.
However, you also need to have level shifters on the input/output lines of the module and the Zener/resistor combination won't work for that purpose. For those lines I would suggest a bidirectional level shifter board like this: https://www.sparkfun.com/products/12009
Well, Crossroads, I had found a site the other day telling resistors do not well, which is not true so I agree with you.
Following this site http://jamesreubenknowles.com/level-shifting-stragety-experments-1741. All depends on choosing the correct resistors for the one means or the other I assume.
But, my question was not what means to use as you can read at my first posting.
To get 3.3V power from 5V, use an LM1117-N-3.3, similar to what the Arduino does (or the same LP2985-33). You waste no more than 10 mA, unlike using a Zener. Need two 0.1µF bypass caps.
No zener diodes are very poor for this because they do not have a sharp knee.
That is the transition between conducting and not conducting does not happen at a fixed sharp point, especially with zeners of such a low voltage.
