Skip to main content
jmjobin
jmjobin
Associate II
December 22, 2020
Solved

B-L072Z-LRWAN1 LoRa®Discovery kit using PB8 and PB9 IC2 with a display. Does not function properly

  • December 22, 2020
  • 7 replies
  • 2028 views

Developing with B-L072Z-LRWAN1 LoRa®Discovery kit with sensor board and GNSS Teseo.

I added an OLED ssd1306 and connected it on IC2 PB8 PB9. I can send commands but when I send data I very often get a display hang. How should I handle PB8 PB9? Should this be terminated? Is it a jumper to set on any of the 3 boards?

This topic has been closed for replies.
Best answer by Tesla DeLorean

I'd use something more aggressive than 10K, something like 2K7 nominally, but perhaps 1K5 in a pinch. You want reasonable rise times in the presence of capacitive load.

7 replies

Tesla DeLorean
Tesla DeLorean
Guru
December 22, 2020

Those OLEDs certainly work on that board. I2C expects pull-ups at some point on the bus pins​. Seem to recall the .96" panels already have pullups, but might depend on make/model. The larger 2.4" ones need converting to I2C and the reset connected.

Have these things running continously for days/weeks​.

I'd look for code level issues, or timeouts that were too tight.

Other devices on bus might not play well together.​

Tips, Buy me a coffee, or three.. PayPal Venmo (See Profile) Up vote any posts that you find helpful, it shows what's working..
jmjobin
jmjobinAuthor
Associate II
December 22, 2020

Thank you Clive for your answer. Looking at the code STM32CubeFunctionPack_LORA1_V2.2.0, I am using the same bus as the sensors and the sensors still work well. I cannot understand what is going on. my code also worked well for several hours and then stops working when I used another brand of display. Replacing back the "working" display did not really help. It hangs regularly. That is why I was thinking about jumpers or terminators to add...

jmjobin
jmjobinAuthor
Associate II
December 22, 2020

I think I found the problem. Tried PullUp resistors 10k did not help.

Tried 5VCC and not 3.3V and it worked for all display. At 3 .3V only one display was OK.

Tesla DeLorean
Tesla DeLoreanBest answer
Guru
December 22, 2020

I'd use something more aggressive than 10K, something like 2K7 nominally, but perhaps 1K5 in a pinch. You want reasonable rise times in the presence of capacitive load.

Tips, Buy me a coffee, or three.. PayPal Venmo (See Profile) Up vote any posts that you find helpful, it shows what's working..
jmjobin
jmjobinAuthor
Associate II
December 23, 2020

Clive, Thank you good advice I will try this too, (1k5).

I have another point that looking at the code I cannot understand is how is the I2C speed sets in the code... STM32CubeFunctionPack_LORA1_V2.2.0

Any idea?

Tesla DeLorean
Tesla DeLorean
Guru
December 23, 2020

Not using that fork, but, on the L0​ the speed is set using a cryptic timing value, which encodes edge and cycle details. I'd expect to find it in the I2C init code or MSP code. Will look when at a computer.

Use a CubeMX wizard to calculate value in a scratch project and paste the constant into your own.​

Tips, Buy me a coffee, or three.. PayPal Venmo (See Profile) Up vote any posts that you find helpful, it shows what's working..
jmjobin
jmjobinAuthor
Associate II
December 23, 2020

Thank you Clive, To go back to the Pull UP resistors, You were right and "you are the best" :-D, I used the 1k8 at 3.3VDC and all is working fine... Thank you... This was the solution.

Terms & ConditionsAccessibility statement