LoRa Thing Plus expLoRaBLE fails with accessory board. Same boards work with Red Board Qwiic

Qwiic System
1

I’m using an i2c scan sketch to test. I’m keeping it simple using the same board, same sketch and same cable. When I connect them to the Red Board Qwiic, the accessory board all reply with their address. When I connect them to the LoRa Thing Plus expLoRaBLE, some boards respond as expected. Others do not. See below.

I’m powered from the USB ports of my laptop for both.

Red Board Quick

0x27, Qwiic GPIO

0x40, 0x76, Qwiic PHT MS8607

0x37 Qwiic MP3 Trigger

0x6C Quad Relay

0x72 SerLCD

expLoRaBLE

0x27, Qwiic GPIO

0x40, 0x76, Qwick PHT MS8607

Qwiic MP3 Trigger - lists all from 0x01 > 0x7F

Quad Relay - lists all from 0x01 > 0x7F

SerLCD - Disconnects USB and hangs

I expect based on the results, its a power issue. Either the expLoRaBLE is not able to supply enough to the current or something else?

I’m looking for advice and recommendations. I’m planning to connect a about 10 devices via the Qwiic bus to the expLoRaBLE if its having issues with 1, there is quite a gap to bridge.

2

What COULD be the issue is the many parallel pull-up- resistors on SCL and SDA line. Many of the devices that are connected to the I2C/QWICC have their own (2K2) pull-up resistors. The more you put those in parallel, the lower the resulting resistance get and the more current is drawn from 3V3 in case of sending an ACK (connect to GND) in responds to their address. Try to cut on the different boards the pull-up resistors JP-x (which one it may be). On a single SCL or SDA line, a single 4K7 to 10K resistor is enough.

3

Thank you. I figured that may be related however for this test, I only have a single additional board connected (in addition to the Red Board /expLoRaBLE) and the on board PU is all default. With a single board the source must be something else.

4

It must be something else. I have a total of a master and slave board and one cable. I’m swapping the accessory board and running the i2c scan each time. All boards work individually on the Red Board Qwiic but only two of the five boards work connected to the expLoRaBLE.

Is it typical that there are power budgets that need to be considered? How would one inject more current onto a i2c bus if thats the case?

5

weird indeed… the ExploRaBLE has an SX1262 in the chip but I would not expect that to take much current when not being used. I assume both boards are programmed with V2.0.6 and in that case they use the same core code and initialization (only different pads/pins). The code will already set a 1K5 pull-up on SCL and SDA pad and 12mA drive strength. Do you experience the same issue when using SDA/SCL2 (on pins 16 and 17)? Could it be I2C-speed?

6

I’ve been strictly using the Qwiic connector. I2C speed I haven’t looked at. Thanks for the idea, I’ll do some research and see if that may be it. I’ve never changed them on purpose so I expect they would be whatever the factory Sparkfun speed is.