Serial connection to Meraki MR18

[heinz.horst]

I'got two used Meraki MR18 and I would like to install OpenWrt on them.
Unfortunately I got blocked already at the UART connection.
I've tried an USB-cable adapter as well as a "real" serial port - sadly with the same result.

After powering on I see just an unreadable scrappy screen instead of clean boot messages.

Any idea what I could try?

[tmomas]

• Faulty ground connection
  How exactly have you connected your serial adapter to the MR18 (Soldered wires, header pins, holding the wires by hand to the PCB pdas...)?
• wrong serial connection settings
  With which settings are you trying to connect?
  Have you tried different settings?

[heinz.horst]

@tmomas
I've tried almost all possible settings - current is: 115200 8/1/N/N (no flow control)

In the meantime I've found another post here.
This post was ponting me to the right direction - I do need a TTL USB converter.

Unfortunately I don't have one - but I have a bunch of Arduino Nano boards around.
So if sombody needs a really cheap USB TTL converter...

1. just take a Arduino board (nano in my case)

2. flash this small sketch on it:

void setup()
{
  pinMode(0,INPUT);
  pinMode(1,INPUT);
}
void loop()
{

}

3. Connect Pin0 -> RX, Pin1 -> TX and Pin5 -> GND

4. Plug your adrunio to your computer, identify the Com Port, connect to the Com Port und you are done if you see the "Meraki" prompt