RAK3172 does not work

Hi there,

We bought a RAK3172 and connected it to our circuit to test it.
It is being used in P2P mode and 30 modules are being tested.
If a problem occurs in the RS422 line, wireless communication is performed using the RAK3172.
RAK3172 is not used because RS422 line is usually used.
It was confirmed that the RAK3172 was operating by disconnecting the RS422 line from sometimes.
I tested it for about a month and there was no problem, but suddenly it was discovered that the wireless was not working.
After searching for the cause, the RAK3172 did not work.
The RAK3172 did not respond even when AT commands were sent.
Even if it is separated from our circuit and connected to USB TO SERIAL for testing Similarly, RAK372 did not respond.

  1. RAK3172 module firmware version

    • RUI_351
  2. RAK3172 module hardware status

    • 3.3V power supply
    • RST: 10k and 100nf connection, MCU connection
    • BOOT: Connect with MCU
    • UART2: Connect with MCU
    • UART1: Connected to MCU IO, but not used and set to LOW.
    • RAK3172 The remaining PINs are not connected to anything.
  3. 21 out of 30 modules do not work

    • For 14 out of 21 badmodules, the RST pin went low approximately every 3.56 ms.
      This symptom is that when the firmware is downloaded to the RUI_342 version, the
      phenomenon of the RST pin falling low disappeared and normal operation resumed.
      After that, I am using it after changing the firmware to RUI_351.
      However, it does not work if you download only RUI_351 from the beginning without
      downloading the firmware to RUI_342.
      You must download RUI_342 for normal operation again.

    • 7 out of 21 bad modules are OK with no RST pin going low
      But UART1 is set to Low.
      The one with this symptom does not work even if the firmware is changed.

How can I prevent the symptoms that do not work as above during use?
If it stops during use, it cannot be used.
And if UART1 is low, please tell me how to make it work again.

Thanks.

Welcome to the forum @JIN

What do you mean with

UART1 is set to LOW

Are you pulling both RX and TX pins to GND?

Connect USB TO SERIAL only to UART2, and UART1 has nothing connected.
The TX and RX PINs of UART1 are 0V.

There are some problems with RUI3 V3.5.x and UART1

I propose you stay on the old version until the problems are fixed. Next release is planned for January 2023