Help with EMF Reader

[kgray9]

Hello all!

I am trying to make a simple (lol) EMF meter that reads the strength range of an EMF. So far I am using a 16x2 LCD, a Nano, a copper loop antenna that I made, and a 3MΩ resistor.

I wired the LCD to the Nano correctly (I got the I2C version ), and wired the antenna to pin A0 with the 3MΩ resistor going from A0 to GND.
Next I made a simple code that just reads the value of the analog pin and prints it on the display and in serial.

The problem is that the readings are strange (pun intended; "ghost meter"). When I place the antenna near a wall outlet or a power cable, the readings spike to about 40 and then immediately drop to 0 again. If I touch and hold the antenna, the readings go up to slowly 350 and then back down and stays on 0 for ~5 seconds, and repeat.

Oh, the wire attaching the antenna to pin A0 is ~6 inches long. The antenna is a loop antenna in a rectangular shape made of 22AWG solid copper (not enameled).

Any ideas what's happening?

Thanks in advance!

Code:

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

int pin = A0;
int reading;
int val;

LiquidCrystal_I2C lcd(0x27,16,2);  //lcd configuration

void setup() {
  Serial.begin(9600);
  lcd.init();
  lcd.backlight();
  lcd.setCursor(0,0);
  lcd.print("EMF");
  lcd.setCursor(0,1);
  lcd.print("Reader");
  delay(3000);
  lcd.clear();
}

void loop() {
  reading = analogRead(pin);
  delay(10);
  Serial.println("Reading: " + String(reading));
  lcd.setCursor(4,1);
  lcd.print(reading);
  delay(300);
  lcd.clear();
}

[jremington]

@kgray9

Any ideas what's happening?

Static charges are transferred to/from the antenna when you touch it, or bring it near conductors. Then the charges leak off.

[kgray9]

Thanks @jremington!

How does this one work in this link then?

DIY Ultra Sensitive EMF Detector

I kind of copied him. His acts as it should.

[jremington]

Do you believe everything you see on the web?

[Paul_KD7HB]

@kgray9

I kind of copied him. His acts as it should.

If you were in exactly the same location when he tested his device, yours would act the same. From your description, your device is working properly. The EMF is different in EVERY location in a building.

[kgray9]

@Paul_KD7HB

From your description, your device is working properly.

Really ?

I do electrician stuff every so often, so I have my favorite pair of wire strippers and a simple voltage detector to make sure the line is off. It has 3 levels of sensitivity and three LEDs to indicate signal strength. I know that this device senses EMF to check voltage, but how would I copy that? It seems very basic. When it is put near a power source, it beeps and all three LEDs light up; when not, nothing happens.

How could I make mine do that, instead of what it is doing ? Not necessarily the three LEDs and the buzzer, but the way it reliably reads an EMF. It seems like I am missing something simple.

Thanks for the response @Paul_KD7HB

[jhaine]

Where does the other end of the loop go? If it's disconnected why use a loop at all?

[Paul_KD7HB]

I don't know. Take the other device apart and see how it is made and copy that.

[Paul_KD7HB]

The wire probe can be in ANY shape. It is a voltage probe, not a current sensor, so the other end cannot be connected to anything.

[EmilyJane]

If you would post , per forum guidelines, a schematic diagram of your circuit (a photo of a hand-drawn schematic is acceptable) and a closeup photo of your actual hardware, people here would probably be more inclined to give you more help.

[jhaine]

@Paul_KD7HB

It is a voltage probe, not a current sensor, so the other end cannot be connected to anything.

Which was my point. TBH I think this project is pointless as it stands, it doesn't measure anything useful.

The device the OP mentions that senses voltage will probably be seeing an alternating electric field generated by the mains. That's a different problem because the field comes from a low impedance source and so isn't discharged by the detector. You could sense that using an analogue input biased at mid-rail with say 2 1Mohm resistors, then looking at the 50/60Hz signal induced by the mains electric field. Clearly insulate the probe so you don't connect mains to the chip!

[Paul_KD7HB]

@jhaine

it doesn't measure anything useful.

Certainly true! But it makes one aware that we are constantly in varying electromagnetic fields, no matter where we go. I know people who became rather paranoid when they learned this!

[jhaine]

Well, electric fields anyway, but not being a loop it won't see magnetic fields...

[EmilyJane]

OP didn’t copy all the code in the project. The referred Hackster project is basically a “peak detector”. OP’s project sees the peaks but immediately clears them from the display. When I mocked up the circuit using my DVM and a 1MOhm resister, I got the same result. If you hold the reading, you get something closer to the Hackster project.

[kgray9]

I figured that since the circuit was simple enough, my explanation would make do.

[kgray9]

Yes. This project is pretty much just to be aware that we are constantly in electromagnetic fields; not so much for a specific measurement of something .

[kgray9]

Ah, thanks @EmilyJane!

That sounds like that is exactly what is going on. Maybe that is how a standard voltage tester works🤔?

[kgray9]

Hello @jhaine

Sorry, im a little lost with your explanation .

[EmilyJane]

Maybe. It could also contain a coil of wire connected to measure an electric field.

[kgray9]

Hmmm. In the tip of the device, you can see a small metal plate that seems to be the antenna.

The voltage detector: