ESP32 CAM ADC Jitter With PWM Servo Feedback

Yes - what you’re seeing is very consistent with the ESP32 ADC/Wi-Fi interaction, not just ARC or the camera skill.

Short answer

For an ESP32-CAM with Wi-Fi active, you want to use ADC1-only pins.
ADC2 pins are not reliable while Wi-Fi is running, and the camera stream can make the timing/noise problem look even worse.

On the ESP32 family, the safe rule is:

• Use ADC1 channels only
• Avoid ADC2 entirely when Wi-Fi is active

Why it happens

Your setup has two stressors at once:

1. Wi-Fi/video streaming
2. Analog feedback reading

On ESP32, ADC2 is shared with Wi-Fi hardware, so readings can become:

• noisy
• stuck high
• erratic
• randomly near 0 or 4095

That matches your symptoms exactly.

What to use on ESP32-CAM

For the common AI Thinker ESP32-CAM, the practical ADC1 candidates are limited because many GPIOs are already used by the camera, flash LED, SD slot, or boot functions.

In general, the ADC1-capable GPIOs are:

• GPIO32
• GPIO33
• GPIO34
• GPIO35
• GPIO36
• GPIO39

But on the ESP32-CAM board, not all of those are conveniently broken out or safe to use.

Important note

Synthiam ARC ports on this firmware are mapped to GPIOs by the firmware, so the exact D-port to GPIO mapping depends on the ESP32-CAM firmware build and board model config.

You’ll want to verify the pin mapping in the ESP32-CAM firmware notes here:

• ESP32-CAM firmware support: https://synthiam.com/Support/Hardware/ESP32-Cam

Best practical recommendation

For stable feedback with Wi-Fi and video running:

• Use an ADC1 pin only
• Prefer a pin that is:
  • not used by the camera module
  • not used by boot strapping
  • not used by the flash LED or SD circuitry

If your current D14 maps to an ADC2-capable GPIO, that would explain the instability.

What I’d try first

1) Confirm the D-port maps to ADC1

Check the firmware’s port mapping for the AI Thinker build and pick a D-port that maps to one of these ADC1 GPIOs:

• 32
• 33
• 34
• 35
• 36
• 39

2) Don’t use getADC("D14")

In ARC JavaScript, use the port constant directly when possible, not a string.

Example:

while (true) {
  var v = ADC.get(D14)
  print(v)
  sleep(100)
}

If you’re using a port that the firmware maps to a bad ADC channel, the syntax won’t fix the underlying issue, but this keeps the command aligned with ARC constants.

3) Slow the sampling a bit

If the servo feedback is mechanically noisy, sample at 50-100 ms instead of faster.

4) Add software filtering

Even with the right pin, servo feedback pots are inherently noisy. A simple moving average helps a lot.

Example JavaScript smoothing:

var samples = []

while (true) {
  var v = ADC.get(D14)
  samples.push(v)

  if (samples.length > 10)
    samples.shift()

  var sum = 0
  for (var i = 0; i < samples.length; i++)
    sum += samples[i]

  var avg = Math.round(sum / samples.length)
  print(avg)
  sleep(100)
}

Wiring notes

Your divider/filter idea is reasonable, but a few cautions:

• Keep the servo power separate from the ESP32-CAM supply if possible
• Common ground is required
• Ensure the feedback wiper never exceeds the ADC input range
• On ESP32, ADC behavior is often better with:
  • a small series resistor
  • a capacitor to ground
  • clean 3.3V-reference-friendly scaling

Also, the ESP32 ADC is generally less linear and more finicky than an AVR or many other controllers.

Best long-term solution

If you need video streaming + stable analog feedback + servo control at the same time, the ESP32-CAM is often not the best board for the analog feedback job.

A more reliable architecture is:

• ESP32-CAM = camera + Wi-Fi + robot control
• Separate EZ-B / controller with better ADC behavior = feedback sensing

Or use a digital feedback servo driver / smart servo solution if you want cleaner positional data.

ARC works very well when the underlying hardware provides stable feedback.

If you want to keep this on the ESP32-CAM

Then the key is:

1. Use ADC1-only pins
2. Verify the firmware port mapping
3. Avoid ADC2 pins entirely
4. Filter in software
5. Minimize servo power noise

Helpful links

• ESP32-CAM firmware info: https://synthiam.com/Support/Hardware/ESP32-Cam
• PWM servo Feedback (ADC) skill: https://synthiam.com/Support/Skills/Servo/PWM-Servo-Feedback-ADC?id=18047
• ARC downloads: https://synthiam.com/Products/ARC

Follow-up question

If you paste the exact D-port mapping from your ESP32-CAM firmware or your firmware #define pin table, I can help identify which specific ARC ports are ADC1-safe on your build.