Noise and Flatline

Start With The Simple Checks

Most first EMG failures come from power, electrode contact, ADC range, or wiring. Do not change the circuit until these are checked.

Common Symptoms

1. High-frequency waveform fills the 0–3.3 V range

If the waveform jumps rapidly across most of the 0–3.3 V range, the electrodes are usually floating or not making good contact with the skin. When the skin-to-electrode path is unstable, the front end can easily pick up enough environmental noise to fill the ADC range.

Wet the skin with a small amount of clean water, or wait until the skin is slightly sweaty. Once contact improves, the waveform should usually shrink back near the 1.65 V mid-rail.

If your development board is connected directly to a computer and you still see high-frequency motion around 1.5–1.8 V, the setup may be picking up power-supply noise. For EMG measurement, run the computer on battery power and unplug the laptop charger.

2. No waveform on skin, stable near 1.65 V

If the waveform stays near 1.65 V and does not change during muscle contraction, the measurement path may be forced to the VREF level.

Common causes include poor electrode contact, VREF being disturbed, IN+ and IN- shorted together, or a bad electrode lead/connector contact. Check the electrodes, wires, connectors, and circuit contacts. Make sure IN+, IN-, and REF/VREF are not shorted or swapped.

3. Muscle contraction is visible, but baseline noise is large

If contraction clearly changes the waveform but the baseline noise is large, the setup is usually picking up strong mains interference from nearby power adapters, power strips, displays, computer chargers, or long loose wires.

Move away from noise sources, shorten wires, and use battery power. If you are viewing the waveform on console.aawlab.com, enable the notch option to remove mains interference. In your own software, add a 50 Hz notch filter.

Flatline

If the waveform is a straight line:

1. Confirm the front end and acquisition board are powered.
2. Confirm the EMG output is connected to the correct ADC input.
3. Confirm ground/reference wiring is shared as required by the product version.
4. Check whether the ADC input range is too small or the signal is outside range.
5. Re-place wet electrodes and check skin contact.

Saturation Or Clipping

If the signal is stuck near the top or bottom of the range:

1. Check the output midpoint of the analog front end.
2. Confirm the ADC reference voltage and input mode.
3. Move away from chargers, monitors, and USB hubs.
4. Try battery power.

Strong Noise

If the waveform is noisy but still reacts to muscle contraction:

• Shorten loose wires.
• Keep the setup away from power adapters and displays.
• Use wet electrodes for the first test.
• Keep electrode contact stable.
• Check whether the reference electrode is placed correctly.

Success Signal

A usable first waveform does not need to look perfect. It should be quiet enough when relaxed and clearly larger during contraction.

If you can see that change, the signal chain is alive and you can improve noise step by step.