I am using D5 and D6 in a Nano Clone (Massduino 328D with CH349G usb) to drive a single amp module input. It work with the input D5 through a potentiometer to reduce the volume on that pin while I run D6 to the same amp input. Attached is a schematic of what I am planning to do as I move from the proto to a PCB. Using blocking diodes to prevent back voltage on the pin that is not in use during output from the other pin? Is this necessary or am I just overthinking the problem?
I'm not worried about the mixing. More about applying the tone signal to a pin that is in output mode. Example: D6 is sending the +5 PWM signal to the amp. This signal will feed back though the parallel connection between D5 and D6. I don't expect this will cause a problem, just being careful.
Ahhh, I see this combines the two signals which are being simultaneously transmitted to the amp. Since I am using an Arduino that can only produce one tone output from one pin at a time, my problem is not a mixing problem, but an assumed isolation problem between the pins. It may not be a problem at all as the pins are pulled to ground when off, but I have never like putting a signal where I did not want or need it.
That doesn't matter. If you mix A and B signal, a mixer functions as a combiner, and if A and B are not simultaneously active, what you have is a signal selector (like a mux). I'm assuming that it is the function you need from your description.
Consider the case where A is active (playing tone) and B is inactive (in this case by virtue of being in a fixed logic state like LOW). A tone of 1/2 amplitude of A appears at the output of the mixer.
The opposite states of A and B result in 1/2 amplitude of B at the output.
So I fail to see how this circuit is deficient for your application. The resistor values, if chosen conservatively, provide enough output to output isolation without diodes. The MOSFET that is "on" in an active output can both sink and source reasonable currents safely.
What is the reason "switched ground" is returned to Arduino pin D7? If the MOSFET is off, it would allow audio amplifier ground current to flow into it, unless I need another coffee.
As a note it is not there now. My initial idea was to see when the Switched ground actually reached ground potential signaling the Nano that the amp was now ready to go. I dropped that and just put in a 100-millisecond delay. The best part is no part, and the best process is no process, right?
