You want to measure a DC voltage. That voltage should be no more than 5V but you want to set the meter to a scale higher than the highest voltage that you expect. If you set it much higher than the voltage that you are measuring you will lose some resolution, but you can certainly start higher and move lower. If I am understand you, then there is a 20VDC scale and that is probably fine. Again, the instruction manual for the meter is your friend.

And how I connect it to router ?
TXD(UART) to RX(router)
RXD(UART) to TX(router)
GND(UART) to GND(router)
And do not connect 3.3v or 5v

 

And how I connect it to router ?
TXD(UART) to RX(router)
RXD(UART) to TX(router)
GND(UART) to GND(router)
And do not connect 3.3v or 5v

Yes, that sounds reasonable to me.

 

Yes, that sounds reasonable to me.

TXD(UART) to RX(router)
RXD(UART) to TX(router)
GND(UART) to GND(router)

Baud rate 115200
Data Bits 8
Stop Bits 1
Flow Control None

And getting same empty screen

Router voltage 3V3 is 0.0.
other ones 3.2-3.3

 

TXD(UART) to RX(router)
RXD(UART) to TX(router)
GND(UART) to GND(router)

Baud rate 115200
Data Bits 8
Stop Bits 1
Flow Control None

And getting same empty screen

Router voltage 3V3 is 0.0.
other ones 3.2-3.3

Did you perform the test on the USB/serial board as described in post #14? If you do that and don't see what you are typing in the putty screen, you either have a bad USB/serial board (either bricked or no driver loaded) or you do not have putty configured properly.

Let's get that step cleared up first.

What does Router voltage "3V3 is 0.0" mean? Are you saying that there is a pin on the Router that you are expecting to be 3.3V and it is not?

In any event, I would suggest you do the test described above first and get that part squared away.

 

Open Putty and what you type should also appear in the Putty window. If the USB/serial board works and is recognized by your PC

It's opens a empty window, when I can type everything I want. When I press enter It goes to the beginning of line and when I type it is overwriting old text.

What does Router voltage "3V3 is 0.0" mean? Are you saying that there is a pin on the Router that you are expecting to be 3.3V and it is not?

Green one is giving 0.0
GND + Green oen 0.0

More here

 

It's opens a empty window, when I can type everything I want. When I press enter It goes to the beginning of line and when I type it is overwriting old text.

Green one is giving 0.0
GND + Green oen 0.0

More here

It sounds like you have a working USB/Serial port board and connection and that is why you can see what you type after you open putty.

I still do not know if your board is transmitting at 3.3V or 5V - we discussed that already and it should be at 3.3V and it should not be at 5V. What is the voltage on the TX and RX pins on your USB/Serial board. One should be 3.3V and the other 0V - neither one should be at 5V. We discussed this already - if it is at 5V and you connected it to the router, you may damage the router. That is why I made such a big deal out of the 3.3V.

As for the router's 3.3V pin being at 0v. I think that could be a problem.

If I am understanding correctly (and I may not be), your router should be plugged in and turned on and I think you should be able to to see 3.3V on the green pin above. Is that the case or not?

See how this guy has it connected in the pic below? He has only three wires going to the router - TX RX and GND.

 

@muzun any updates? Did you get it sorted out?