How to connect to I2C on Heltec Lora32 V3

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1

I have a Heltec Lora32 V3. Now I wanted to try the environment telemetry with a BME680 sensor. Unfortunately, I cannot access the I2C connection on GPIO 17 and 18 as it is used for the OLED screen and not broken out to the headers. I looked through the documentation, the code on Github and the logs from my device without finding a solution. Maybe I have overlooked something? Else, I see the following options:

  1. Hack the board and break out GPIO 17 and 18
  2. In some way, add support for the second I2C and map it to GPIO 47 and 48

None of these options seems great… Any thoughts?

2

Probably you can use T1 and T2, just above pin26/48 and labeled 17/18, the testpads connected with OledSDA and OledSCL. If you can solder 2 small wires to these pads (+ GND & V+) you have your I2C bus and still use the OLED. If you use GPIO 47&48 your onboard Oled will be useless and you have to redefine the I2C pins in the source and recompile yourself.

So I would go for option 1.

3

Great, thanks Costco. I found the two small pads, so I’ll wire them up and test.

5

did it work? if yes, could you please share a shematic or photo? i d like to try the same…
Thanks

6

Here is a video describing the modification to the Heltec V3 I did to enable sensing with an SHT30 temp and hum sensor:

"Here is a Heltec Lora32 V3 module with two extra pins added to the board to give easy access to the i2c SDA and SCL pins for Environmental Sensing in Meshtastic firmware.
Pin 17 is SDA and pin 18 is SCL.

I tinned the two pads on the circuit board with silver bearing electronic solder and tinned the tips pf the two pin male header and, using the “helping hands” jig I soldered the pins to the board.

Using the Meshtastic web flasher (flasher dot Meshtastic dot org) on an Opera web browser on Linux, I flashed Meshtastic 2.2.23 and then, using the Meshtastic android app, I scrolled down to the “Module Configuration” section and clicked on “Telemetry” and enabled the “Environment telemetry” and enabled “Displayed on screen”, etc.

And it WORKED! Even though the SHT30 sensor is on the same i2c bus as the OLED display, it did not mess up the OLED display. If I probed the i2c pins with a voltmeter, it messed up the display."

7

Hello! I have meshtastic firmware on my Heltec V3
I am trying to ad the card kb using this information. Power cables are ok, and susibg puns 17 and 18.
When I boot my heltec screen is off. I don’t know what else should I try.
No les or lights are seen on the kb… :thinking:
Thanks

8

Did you ever get the CardKB working on the Heltec V3?

9

Yes
https://youtube.com/shorts/VfPcEuGCrhs?si=z7Kx8VS7283W5nUi

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