Pi communication

Projects General Guidance
1

I have a 3.3v pro mini arduino board that I want to recv commands from a raspberry pi, possibly send acks or responses, that part less important than the first direction. Pro mini has no usb onboard and I do not want to add an ftdi or anything. I2c, spi, uart/serial should all be options, right? Which to use, and why?

The commands will be like 2-5 chars at a time, and once a minute or even less frequent. Any responses will probably be a 0/1 or Y/N single char, have not thought that far ahead yet

2

Use pi serial port.

3

So, pi tx to arduino rx, pi rx to arduino tx, no level shifter or buffer, and use the Serial functions on arduino? I have a python serial lib for the pi side.

4

blah44:
So, pi tx to arduino rx, pi rx to arduino tx, no level shifter or buffer, and use the Serial functions on arduino? I have a python serial lib for the pi side.

Right?

5

No.

Simplest way is just to plug the Arduino into the Raspberry Pi and talk to it serially.

With connecting pins you need a resistive divider from the Arduino TX to the Pi's RX and a single transistor from the Pi's TX to the Arduino's RX.

6

OP is using 3.3V version arduino pro so a direction connection as OP described should be sufficient.

7

Sorry missed that.
I would still use the direct method and use the USB port.

8

In case of USB port, get a cheap USB TTL adapter for a few USD. The hard part if you use C/C++ on PI is to disable all the crappy terminal features of a serial port. If you use python, there seems to be an easy way to do it. What does the book author say (GM)?

9

liudr:
OP is using 3.3V version arduino pro so a direction connection as OP described should be sufficient.

Thanks liudr!

10

What does the book author say (GM)?

No need for anything just plug the Arduino into the Pi with a normal USB cable.

11

Grumpy_Mike:

What does the book author say (GM)?

No need for anything just plug the Arduino into the Pi with a normal USB cable.

The pro mini has no usb, in fact adding usb via ftdi costs more than the pro mini itself!

Any advantage to usb given that?

12

Any advantage to usb given that?

No none at all.

Sorry for the confusion, just connect up the three wires.

13

Grumpy_Mike:
No none at all.

Sorry for the confusion, just connect up the three wires.

No problem at all, the input is always appreciated!

three wires? tx+rx, then what, ground? do they need to share a common ground for serial to work?

14

do they need to share a common ground for serial to work?

Yes all things need a common ground.
This page tells you why:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

15

Grumpy_Mike:
Yes all things need a common ground.
This page tells you why:-
http://www.thebox.myzen.co.uk/Tutorial/Power_Supplies.html

Great - thanks again!