ADC & Smoothing

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mop

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Hi everyone,

I am currently getting further and further in to flight sims, and have decided that I need a custom controller. While I have been programming for years I have no electronics knowledge. This is something I am keen to rectify to the extent that I can play around with Arduino/Teensy and similar for fun projects.

My current main flight sim is Il2 Cliffs of Dover, and I am branching out in to DCS world. One of my most immediate controller issues is that I need accurate trim controls. I currently have a CH throttle quadrant which the axes give about 69 degrees of turn? I was thinking of going for some 1, 3 or 5 turn pots.

So I bought a Teensy 3.1 and headed down to Jaycar for some parts. End result code is below a very basic diagram.


Code: 
void setup()
{                
  Serial.begin(38400);
}

int val;

void loop()                     
{
  val = analogRead(4);
  Serial.print("analog 0 is: ");
  Serial.println(val);
  delay(250);
}

Pin 4 should be AGND
Pin 6 should be 3.3V
Pin 18 is A4.

Untitled.png

My output is this
analog 0 is: 716
analog 0 is: 738
analog 0 is: 758
analog 0 is: 784
analog 0 is: 742
analog 0 is: 736
analog 0 is: 759
analog 0 is: 744
analog 0 is: 741
analog 0 is: 810
analog 0 is: 764
analog 0 is: 713
analog 0 is: 729
analog 0 is: 724
analog 0 is: 747
analog 0 is: 748
analog 0 is: 753
analog 0 is: 728
analog 0 is: 714
analog 0 is: 760
analog 0 is: 759
analog 0 is: 760
analog 0 is: 743
analog 0 is: 715
analog 0 is: 760
analog 0 is: 723
analog 0 is: 754
analog 0 is: 728
analog 0 is: 715
analog 0 is: 804
analog 0 is: 713
analog 0 is: 744
analog 0 is: 737
analog 0 is: 743
analog 0 is: 772
analog 0 is: 750
analog 0 is: 732
analog 0 is: 762
analog 0 is: 737
analog 0 is: 769
analog 0 is: 776
analog 0 is: 722
analog 0 is: 717
analog 0 is: 730
analog 0 is: 765

As you can see values vary wildly. I have been poking around the forums so have tried a few capacitors between the 3.3V and AGND but that makes no difference. I really don't know what I am doing. Can anyone suggest how I should be troubleshooting this?
 
A couple of things: Swap pin 6 for AREF. That should be quieter. For even tighter control, tell the teensy ADC to use a external AREF and use a shunt style voltage regulator to pull the voltage down to 3V or less.

A 0.1uF cap from A4 to AGND should also smooth things by creating a charge reservoir and RC filter - the teensy 3 doesn't handle input impedance over a few kOhms well. Even better would be use of a buffer op-Amp.

Last but not least, put a 100uF cap from 3.3V to GND. There may be something else going on (communications?) that is sagging the local voltages.
 
Constantin said:
A couple of things: Swap pin 6 for AREF. That should be quieter. For even tighter control, tell the teensy ADC to use a external AREF and use a shunt style voltage regulator to pull the voltage down to 3V or less.

A 0.1uF cap from A4 to AGND should also smooth things by creating a charge reservoir and RC filter - the teensy 3 doesn't handle input impedance over a few kOhms well. Even better would be use of a buffer op-Amp.

Last but not least, put a 100uF cap from 3.3V to GND. There may be something else going on (communications?) that is sagging the local voltages.
Click to expand...


Thanks for the replies. I have more questions.
1. What is the recommended way to connect to AREF for bread boarding given that it is on the "inside row" of pins and I have soldered header pins to both outside rows? I could solder a header pin to AREF and use an alligator clip, however that just seems nasty.
2. Does consistent 3.254v count as voltage sag, or only if I see it dip. I get that from AREF to AGND and from 3.3V to AGND? If this voltage is consistent will it be an issue or only if it changes over time/load?

Thanks.
 
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