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.


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

Hello, The topic is old but I have the same problem. RST pin pulls to ground at different times. It doesn’t have a specific pattern, sometimes it works for days, but then it goes to the ground and the device turns off and on. As you suggested there is only resistor and capacitor on the RST pin.

The latest firmware is installed but the same problem persists. The same problem persists in custom firmware.

I’ve purchased a lot of RAK3172 and never had such a problem with previous modules. But there are such problems with the modules I bought in January 2023.

I am waiting for your support.

Hi Suffet,

What exactly do you mean with RST pin pulls to ground at different times?

The RAK3172 does not control the RST input and we had no hardware change since a year.

What RUI3 version are you using at the moment?

Are you using the RAK3172 on a custom PCB? If yes, can you share your schematic?

I uploaded the schematic and layout. Technically, I should only see VCC voltage on the RST pin. But sometimes it is 0.7V, sometimes 1.2V. For this reason, the module behaves unstable and resets or does not start at all. When it is 0.7V, when I give external VCC from outside, the module starts to work.

Thanks for the (partly) schematic and the PCB layout.

  1. There is no need to pull BOOT0 to GND. That is already done inside the module.
  2. Where else is your RESET_RAK signal going? Your schematic shows only the pullup and capacitor. But on the layout the signal is obviously going somewhere else as well.

Did you check the solder points on all components of the RESET_RAK signal? Your fluctuating voltage on the reset pin can be caused by anything that is connected to it. Inside the module is nothing connected to it and the STM32 MCU cannot pull it down by itself.

Actually, only the way to the programmer connector (TagConnect) goes. The RST pin is not connected to another module.

Did you check the solder points of all components on the RAK_RESET signal.

As I said, the module itself cannot pull it’s RST down by itself.

What firmware are you using? Are you using our RUI3 based AT command firmware, a custom firmware written with RUI3 or are you using a firmware based on STM32CubeIDE?

I am using software based on MBED OS. As I said, we are actually not newbies on the RAK3172. We’ve been using it since it first came out. So far, we have delivered a total of 5000 devices. However, we are experiencing similar problems on 1000 modules we bought in January.

Hello Saffet,

I am following this now in our customer support desk, as it is easier for me to keep our R&D in the loop there.