PLEASE HELP! RAK4630 + RAK19003 not working with ATGM336H GPS Module

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1

I have been banging my head on this GPS problem for a few days now. Any ideas what I am missing?

I am trying to connect a ATGM336H GPS model to a wisblock (RAK4630 + RAK19003) running firmware 2.3.6. I have the wired as follows:

GPS - RAK 19003
VCC - J6 pin 1 VDD (3.3V)
GND - J6 pin 2 GND
TX - J7 pin 1 RX1
RX - J7 pin2 TX1

The Meshtastic Position settings are as follows:
GPS Receive GPIO - Pin 33
GPS Transmit GPIO - Pin 34
GPS EN GPIO - Unset

The serial log shows that communication is not happening with the GPS.

DEBUG | ??:??:?? 8 [GPS] Probing for GPS at 38400
WARN  | ??:??:?? 9 [GPS] Failed to find UBlox & MTK GNSS Module using baudrate 38400
DEBUG | ??:??:?? 11 [GPS] Probing for GPS at 57600
WARN  | ??:??:?? 13 [GPS] Failed to find UBlox & MTK GNSS Module using baudrate 57600
DEBUG | ??:??:?? 15 [GPS] Probing for GPS at 115200
WARN  | ??:??:?? 16 [GPS] Failed to find UBlox & MTK GNSS Module using baudrate 115200
DEBUG | ??:??:?? 18 [GPS] Probing for GPS at 9600
WARN  | ??:??:?? 19 [GPS] Failed to find UBlox & MTK GNSS Module using baudrate 9600
DEBUG | ??:??:?? 21 [Power] Battery: usbPower=1, isCharging=1, batMv=3352, batPct=14
DEBUG | ??:??:?? 21 [GPS] Probing for GPS at 9600
WARN  | ??:??:?? 23 [GPS] Failed to find UBlox & MTK GNSS Module using baudrate 9600
DEBUG | ??:??:?? 25 [GPS] Probing for GPS at 4800
WARN  | ??:??:?? 26 [GPS] Failed to find UBlox & MTK GNSS Module using baudrate 4800
DEBUG | ??:??:?? 28 [GPS] Probing for GPS at 38400
WARN  | ??:??:?? 30 [GPS] Failed to find UBlox & MTK GNSS Module using baudrate 38400

The GPS module is good as it works with a HeltechV3.
I have also double and triple-checked the soldering and reflowed it several times.
I tried switching the RX and TX pins settings and that didn’t resolve the issue.
I have read a number of similar posts but none seem to give a clear explanation of how to resolve it.

Any help would be much appreciated. Thank you.

2

This morning I realized that these settings are likely wrong. They should likely be the following.

The Meshtastic Position settings are as follows:
GPS Receive GPIO - Pin 15
GPS Transmit GPIO - Pin 16
GPS EN GPIO - Unset

Unfortunately, I still can’t get communication with the GPS.

Still working on it.

3

Mode good progress on this today.

After probing around the 19003 I found that it’s TXD1/RXD1 are actually connected to UART1 on the RAK4630.

After digging deeper I found that I was using version E of the RAK19003 base board. On this version of the board they changed what was connected to J7 from UART2 to UART1.

It’s very frustrating that I can’t find any documentation for version E.

Anyway, I tried assigning pins 19/20 for the GPS pins and it still didn’t work. But when I changed the serial interface in /firmware/variants/rak4631/variant.h then it started working!!! See the change below.

/*
 * Serial interfaces
 */
#define PIN_SERIAL1_RX (19)
#define PIN_SERIAL1_TX (20)

So that is great news but the question I have now is, why didn’t it work when I changed the GPS pins in the settings? Also, is there an easier, better way to solve this pin reassignment that doesn’t require building custom firmware?

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