This may be me but here is the situation
I am communicating via the I2C bus to a Devantech SD21 using an Ardunio Mega 2560
If I use the Arduino on board 5 volt and ground everything works ok.
If I try to use 5 volts to the SD21 and simply use the SDA/SCL from the Ardunio the sketch hangs, the 1st time it attempts to end the transmission.
It acts as if the SD21 is not powered by the external power, I did verify that power does exist at the appropriate pins on the SD21.
Am I missing something obvious ? Have noticed this problem with other sketches as well that use the servo library to fire up an R/C ESC.
Any troubleshooting suggestions
When you do this
"If I try to use 5 volts to the SD21 and simply use the SDA/SCL from the Ardunio the sketch hangs, the 1st time it attempts to end the transmission. "
are you connecting the 2 grounds together?
Thanks for the very quick reply
No actually I am not, to connect the grounds, I am assuming the ground on the SD21 will go to ground on the Arduino, does it matter which one ? I am assuming you would go to the ground beside the 5 volt pin ?
Yes. All grounds must connect together. The Gnd on the header is a convenient location.
That resolved the problem. I appreciate the assistance.
Glad to help.