5 replies to this topic

[GDSever]

I haven't gotten a Mini yet (after the holidays, more than likely) but I was looking at the schematic and noticed that there are already 10Meg resistors tied between the SCL and SDA lines and +3.3V...

So does this mean that you do NOT need to provide external pullups (typically 4.7k, right?)

Just curious - I suppose I'll find out the first project I try to use I2C with a Mini...

[Chris Walker]

HI GDServer, The 10meg resistors are effectively "dummy resistors." Or as I tend to call them "infinite-ish resistors". If a commercial customer orders a special batch of Netduino Minis, we can replace them with 4.7K or other value resistors. But for standard use, they'll have pretty much zero effect. Since I2C can be driven by 3.3V or 5V and because I2C resistor values change based on voltage and # of devices, we've left them off to enable maximum flexibility for users. Chris

[GDSever]

Thanks for the info - Can't wait to get my hands on a Mini and take it for a test spin.

[Anatoly]

Hello! I using Netduino mini and want to connect on I2C port one device - LIS 331 accellerometer. Please tell me how wright connect it? What nominal resistors place from SDL, SCA to VCC wire? And second - I planning power mini from +5.5V (USB port) but LIS 331 powered maximum 3.3 V can I use 1 LED for drop down power from 5.5 to 3.3? Or best offer will be using LM317L(with resistors defferential) current converter?

[Frode]

Hi Anatoly, 

for the pullup resistors for SDA and SCL you can just try to use 4.7k ohm.

 

For powering the LIS 331 you should use a 3.3V regulator. THe LM317L will work just fine, but it would be easier to use something like MC33269DT-3.3G instead, since it doesn't require any external components.

[Anatoly]

Thank you Frode! You just save more time for me! Regards.