Reading EMG signal using analogread()

Projects General Guidance
1

I have a working circuit that detects spikes in EMG upon muscle contraction: I can read the output successfully on the oscilloscope:

EMG Spike
EMG Spike2320×1712 503 KB

The maximum amplitude of the spike is around 1.2V which should be well within the 5V limit of the analog pins. However, I essentially just see a random constant value each time which doesn't change upon contraction on the serial monitor on the Arduino IDE.

The code is pretty simple, I tried increasing the baud rate from 9600 to 115200 but it doesn't solve the issue:

void setup(){
  
  pinMode(A1, INPUT);
  Serial.begin(9600);
}

void loop(){
  float sensorValue  = analogRead(A1);
  EMG_Voltage = (sensorValue*5.0/1023.0);
  Serial.println(EMG_Voltage);
  }

Hardware setup:

I have connected the circuit output to pin A1. The circuit is powered by 9V batteries and the arduino is powered by the laptop. I only have 1 connection between the Arduino and the circuit, which is from circuit output to A1.

I suspect there is something wrong with the hardware setup or the code, as the circuit is functional as confirmed by the oscilloscope. Could I please get some help on this front? Thanks.

2

Try adding a connection between the Arduino ground and the mystery devices ground, so you have a complete circuit!

3

I did try that, but the reading still looks nothing like the oscilloscope. Do you think there's anything else I'm missing in the hardware setup?

4

We can't see your hardware setup.

5

sorry but I cannot understand the oscilloscope trace. both blue and yellow traces seem to have a 2 mV scale. The yellow trace barely makes it to 0.5 and the blue trace seems to overload the scale. They seem to be changing 3 separate times. Why do you say they are at a random constant value?

6

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