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Topic: Powering up OLEDs with negative PWM (Read 970 times) previous topic - next topic


. . . However, although the Arduino input is clearly seen in the oscilloscope, the output remains 0 . . .
But it's not clear to us unless I have missed an attachment somewhere.

. . . Please, let me know if you think something is wrong with the wiring. . . .
I think there is something wrong with the way you are using your oscilloscope as I implied in my previous post.



Frankly, I think there is something completely wrong with this whole discussion.  Suggesting an OLED display requires negative voltages or PWM simply makes no sense, and everything else follows.

If you want a negative voltage, you use the part designed for that purpose - an ICL7660/ MAX1044, LM2664 or LT1026.



I tried to use a non-inverting configuration to check if my op amp was working as I was afraid that maybe the power supply was not providing a negative voltage and that was why I couldn't see any inversion in the output. I don't know if I am not using the oscilloscope correctly but I only have issues when I am trying to see the output of the op amp. The Arduino input is always there, even when I change the duty cycle. Considering the fact that the only difference between these two signals should be the amplitude, I cannot imagine why the oscilloscope is the problem. Is there anything that I may be missing? Also, I had checked the charge pump circuits but I wasn't sure if the will work with the PWM function. I thought that an op amp would be much easier to implement and I had used it in the past for filtering without any issues. I think I may need to buy a charge pump circuit and test it. 


I cannot imagine why the oscilloscope is the problem. Is there anything that I may be missing?
Yes.  You are missing the whole concept of oscilloscope triggering and input coupling and why both are essential if you want to correctly observe the difference in phase and level between two signals. 

You can observe most characteristics of a single signal without knowing much about these concepts but it's a different story when you want to compare two signals.

It is quite possible that your inverter is operating properly but your measurement techniques are leading you to believe that it is not.



You need to connect the 0V line from the +/-15V power supply to the Arduino 0V, otherwise the circuit will just behave like a 20K resistor connected to the Arduino PWM pin. Add some decoupling near the amplifier fro 0V to each rail.

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