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Reading an output analog pin with an input analog pin

I am having a hard time understanding why I can't read one analog pin's output with another analog pin. The docs state to put a delay in between, which I've done (I've tried up to one second with the same results). I've got this minimized code:

void setup() {
 Serial.begin(9600);
 pinMode(A0, INPUT);
 pinMode(A5, OUTPUT);
}
void loop() {
 for (int i=0; i<1024; i++){
 analogWrite(A5, i);
 delay(100);
 Serial.println(analogRead(A0));
 }
 Serial.println("done");
 delay(10000);
}

When it starts, it displays 6-9 for a few dozen iterations, then suddenly jumps to ~1018 and remains throughout the rest of the run.

A5 is connected directly to A0 via a 4" jumper cable. Nothing is connected to AREF. If I connect AREF to 5v, the output does not change but by a single digit. If I connect it to ground, it immediately outputs 1023.

I'm hoping this is a "do'h" moment here. Can someone please let me know what I'm not doing correctly?

Update: This is a legit Arduino Uno R3 board. When I connect A0 directly to 5v+, I get 1023 as expected as the output.

Answer*

Your program is correct and I suspect the error is in the hardware. Arduino uses its internal timer and creates a high frequency PWM on the corresponding pin upon a `analogueWrite()` is called. Here what we should notice is the DC switching in the appropriate pin is not noticeable in most cases. (If you give it to an LED you can adjust its brightness). 

 But what you have done now is not correct. Since there is no current flowing in the pin there will not be a analogue voltage actuality. It is 5V and 0V switching in a high frequency. Those are the values which the `A0` pin will see. 

So try fixing a capacitor between the pin and the ground. and a 1k resistor to create a slight current flow to stabilize the voltage. then let us know your readings.







![schematic](https://i.sstatic.net/8XweH.png)

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Thanks for this, but I believe the answer that states that I was incorrectly assuming that the A'N' pins were analogWrite() capable is correct. I definitely know I had current flow without need of a resistor, capacitor or other intermediaries. I made bold mis-assumptions as to what pins can do what.

stevieb
– stevieb

07/22/2017 03:11:51
Commented Jul 22, 2017 at 3:11
This answer completely misses the issue. No, you do not need the pin to source current in order to have a well defined voltage. And your 1 µF capacitor can damage the output pin due to the inrush current.

Edgar Bonet
– Edgar Bonet

07/22/2017 12:00:32
Commented Jul 22, 2017 at 12:00
@EdgarBonet Srry, it should be .1uf. So do you mean to use analogueRead() and read a PWM value insted of a real analogue voltage between 0v and 5v.

danial weaber
– danial weaber

07/22/2017 12:09:51
Commented Jul 22, 2017 at 12:09
You wrote: "do you mean to use analogueRead() and read a PWM value [...]". No, I mean what I wrote, nothing more.

Edgar Bonet
– Edgar Bonet

07/22/2017 13:15:08
Commented Jul 22, 2017 at 13:15

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