ADC Graph Spikes On Mega

Yes - what you’re seeing is very consistent with power/ground noise or ADC sampling noise caused by the servos moving, not the Sharp sensor itself.

A few key points for ARC + Arduino Mega firmware:

What ARC is doing

• ADC0 on the Mega is read as a value from 0-255 in ARC.
• That’s a scaled representation of the Mega’s analog reading, not a special filtered mode.
• ADC Graph does not average/filter the signal for you - it displays the raw ADC value it receives.

So if the servo movement is injecting noise onto the analog reference, sensor ground, or 5V rail, ARC will faithfully show those spikes.

Why the spikes happen even with a multimeter

A multimeter averages over time, so it can miss very short transient dips/spikes. Your sensor may look stable on the meter but still be producing:

• brief ground bounce
• 5V sag
• ADC reference noise
• EMI from servo wiring/current surges

Those can easily push the sampled ADC reading to 0 or 255 for a moment.

Recommended hardware approach

1) Keep servo power separate

You already did the right thing here:

• Servos on a separate BEC/supply
• Common ground between BEC and Mega

That’s correct.

2) Improve grounding layout

For the cleanest analog reading:

• Run sensor ground directly back to the Mega ground
• Run servo ground directly back to the BEC ground
• Tie the grounds together at a single star point
• Avoid daisy-chaining the sensor ground through servo current paths

This is often the biggest fix.

3) Add a small RC filter on the sensor output

Yes, a small input filter is commonly used for noisy analog sensors.

A good starting point:

• 1 k series resistor from sensor output to A0
• 0.1 F capacitor from A0 to GND

That creates a simple low-pass filter to blunt short spikes.

If the reading becomes too sluggish, reduce the capacitor value or resistor slightly.

4) Decouple the sensor locally

You already added caps on Vcc/GND, which is good. I’d keep:

• 0.1 F ceramic
• 10-47 F electrolytic near the sensor

5) Keep analog wiring short and away from servo power lines

Even twisted pair helps, but also:

• avoid running analog wire parallel to servo leads
• don’t bundle sensor signal with PWM/servo power wiring

ARC-side recommendation

ADC Graph

ADC Graph is fine for monitoring, but it is raw input only. It does not have built-in smoothing/oversampling controls.

Best practice

Use a script to read ADC repeatedly, average it, and then:

• log it
• publish it as a variable
• use it for logic

If you want a display, you can create a script-driven visualization instead of relying only on ADC Graph.

Your averaging idea is exactly the right direction

A simple moving average in ARC JavaScript is a good fix.

Here’s a cleaner version:

var sum = 0;
var samples = 20;

for (var i = 0; i < samples; i++) {
  sum += ADC.get(ADC0);
  sleep(5);
}

var avg = Math.round(sum / samples);
print("avg=" + avg);
setVar("$SharpFiltered", avg);

If you want, you can use that variable in other ARC skills or scripts.

If you want even better smoothing

Try:

• 10 samples for responsive behavior
• 20-30 samples for heavy smoothing

You can also do a median filter or reject impossible jumps, which helps with occasional servo-induced spikes.

Example simple spike rejection:

var value = ADC.get(ADC0);
var last = parseInt(getVar("$SharpLast", value));
var filtered = value;

if (Math.abs(value - last) > 80) {
  filtered = last;
}

setVar("$SharpLast", filtered);
print("filtered=" + filtered);

Important note about servo ports

On the Arduino Mega firmware in ARC, servo ports like D0 and D1 map to Mega pins 22 and 23, as you noted. That part is fine.

The issue isn’t the servo ports themselves - it’s usually the high current switching noise when the servos move.

My recommendation order

Try these in this order:

1. Star ground the sensor and servo supplies
2. Add 1 k + 0.1 F RC filter on A0
3. Keep sensor wiring short and separated from servo wiring
4. Use a scripted average for readings instead of raw ADC Graph for logic
5. If needed, use a median or spike-rejection filter

ARC configuration suggestion

• ADC Graph: keep it for live monitoring
• Script: read ADC0, average it, and use the filtered value
• Sampling: 200-500 ms is fine for display, but the script can sample faster if needed

Useful reference

• Arduino Mega firmware info:
  https://synthiam.com/Support/Hardware/Arduino-Due-Mega
• ADC Graph skill:
  https://synthiam.com/Support/Skills/Adc/ADC-Graph?id=16091

If you want, I can write you a JavaScript filter script for ARC that:

• averages the Sharp sensor,
• rejects servo-caused spikes,
• and updates a global variable you can use in other skills.