Relay module error

I have a problem for sending signal to relay module.
What I know is,
when relay module get a high signal from Arduino, COM and NO is connected.
On the other hand, when relay module get a low signal from Arduino, COM and NC is connected.
By the way there was a problem at signal.
I've commanded Arduino to send low signal. But Arduino doesn't send low signal to relay module.
Here is my main part of sketch and Serial monitor

  • In Serial monitor, you don't need to mind below things
    Calibration word 2 = DC1B 56347
    Calibration word 3 = 8C1A 35866
    Calibration word 4 = BD1D 48413
    c1 = 22957
    c2 = 1693
    c3 = 756
    c4 = 560
    c5 = 880
    c6 = 27
    D1 - Pressure raw = 17629
    D2 - Temperature raw = 28200
    Real Temperature in C = 27.00
    Compensated pressure in mbar = 10002
    Compensated pressure in mmHg = 750.21

  • What you should mind in Serial monitor is just
    "LOW pressure"

You can see 'else' is working well so that Serial Monitor prints "LOW pressure"
But in 'else',
'digitalWrite(3, LOW)' doesn't work.
Because you know, Serial Monitor doesn't print "LOW"
Serial Monitor prints "LOW" only if port 3 send low signal.

Like this.
So I want to solve the problem that port 3 doesn't send low signal,
even though 'Serial.println("LOW pressure") is working well.
I'm South Korean, and I have low level for english so you can get hard to understand what I'm
talking about.
Please understand me.

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3 will never equal LOW


will, however, equal LOW if pin 3 is LOW

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Thanks. Now it is solved :slight_smile: