Asked
— Edited
I seemed to be having issues with I2C BlinkM's I keep adding the control to the layout and connect the blink M to one of the i2C ports and it disconnects the EZB, every single time. To make sure I have connected the wires correctly could someone point me to a call out that has the break down of the I2C ports, i.e +,-,c,d
Thanks in advance.
is this one ?
http://thingm.com/fileadmin/thingm/downloads/BlinkM_datasheet.pdf
d = I2C SDA
c = I2C SCL
source:
https://www.ez-robot.com/Tutorials/Files/EZ-Bv4%20Datasheet.pdf
1) It's not wired correctly - which is why it's disconnecting.
2) the i2c address is specified incorrectly
There are a few different blinkm versions and revisions.
blinkm min product info:
https://thingm.com/products/blinkm-minm/
EZB is 3.3v
did you used that device before with EZB ?
Their pull-up resistor values on the SDA and SCL lines may also have changed. You could try placing low value (330 to 1kohm) resistors on your wiring harness (SDA to VCC & SCL to VCC) to place them in parallel with the pull-up resistors on the board. Putting these parallel resistors in place with decrease the resistance on the SDA and SCL lines pulling them up stronger.
I need your input:
Q1)
I traced the EZB pcb and it seems EZB does not have pull-ups on SDA, SCL lines, neither a resistor in series, can you confirm this ?
Regarding the Pull-Up values, several times I've used 4.7K with STM32F103, STM32F205 and other 3.3v micro-controllers.
When adding 2 devices with same values 4.7K brings down to 2.35K and still works, but if i bring down below <1.5K i had problems.
I know there are other factors:
1) cable length (let's assume we are using normal distances 30 cms)
2) I2c Bus speed
Q2) EZB I2c BUS Speed ?
*** EDIT: The default value is 100 kbit/s and can be configured in the ARC
Q3) I never heard before the recommendation for 330 to 1K, Isn't the value too low ?
Q4) Can you explain why the recommendation is different for EZB when compared to other/same 3.3 micro-controllers ?
*** EDIT 2:
STM32F205 (EZB microcontroller)
http://www.mouser.com/ds/2/389/stm32f205rb-956262.pdf
page 114
When you have long wires, the series resistors limit the slew rate, but i believe we don't need them.