July 19, 2013 AT 2:00 am

RPi.GPIO Basics @Raspberry_Pi #piday #raspberrypi

We really like this review of the basics via raspi.tv and hope you do, too!

It struck me the other day that I’ve published some fairly advanced RPi.GPIO tutorials, (e.g. interrupts and PWM) but not done anything more basic, apart from the Gertboard examples. So here’s an attempt to remedy that situation.

Over the next few days, we’re going to have a walk around Ben Croston’s RPi.GPIO, which is now at version 0.5.3a. Some of this stuff may be new to you even if you’ve been using RPi.GPIO’s more advanced features, so it’s worth having a look.


Part 1: “how to check what RPi.GPIO version you have” starts out with:

RPi.GPIO_.VERSIONb

It’s quite useful to be able to find out what version of RPi.GPIO you have. Some features require a recent version, whereas others work with older versions. For example, interrupts were added at 0.5.1, PWM at 0.5.2 and with 0.5.3 some bugs have been squashed.

You don’t have to write or run any programs to find out which version you have. You can do it very quickly in a live Python session. If you don’t know how to do that, it’s a great way of testing things out in Python.

Get started with Part 1 here.


Part 2: “how to check what Pi board Revision you have” follows up with:

P5-holes

It all started in September 2012. The Raspberry Pi Foundation went and made some improvements to the Pi. How dare they!! ;) Seriously, though, there were some significant improvements to the Pi and a Rev 2 version was launched with double the RAM and some other changes/additions/improvements.

This threw up some minor headaches for developers because some of the GPIO pinouts were changed and some new GPIO ports were made available on a brand new “solder it yourself if you want it” header called P5 (see the leaning header of Pi5a)

GPIO 0 became GPIO 2 (P1 pin 3)
GPIO 1 became GPIO 3 (P1 pin 5)
GPIO 21 became GPIO 27 (P1 pin 13)

The two i2c buses were swapped around:
SDA0 became SDA1 (P1 pin 3 alternative function)
SCL0 became SCL1 (P1 pin 5 alternative function)

Some new GPIO ports 28, 29, 30, 31 were made available if you solder on P5 header.

Read Part 2 here.


Part 3: “how to Exit GPIO programs cleanly, avoid warnings and protect your Pi”:

Screen Shot 2013-07-15 at 12.17.18 PM

RPi.GPIO provides a built-in function GPIO.cleanup() to clean up all the ports you’ve used. But be very clear what this does. It only affects any ports you have set in the current program. It resets any ports you have used in this program back to input mode. This prevents damage from, say, a situation where you have a port set HIGH as an output and you accidentally connect it to GND (LOW), which would short-circuit the port and possibly fry it. Inputs can handle either 0V (LOW) or 3.3V (HIGH), so it’s safer to leave ports as inputs.

Read Part 3 here.


Part 4: “setting up RPi.GPIO, numbering systems and input”:

Rev2-GPIO-bold

Well, today is the day we actually get to use RPi.GPIO a little bit. But, before we get to that, you should know about the two different numbering systems you can use with RPi.GPIO.

If you take a look at the main GPIO header (P1) of the Raspberry Pi, you’ll see that there are 26 pins. The top left pin (as we look at this photo) is called pin 1, the one to the right of it is pin 2. So the next row is 3, 4 etc. and on down to 25, 26. This is how pin headers are numbered.

Check out Part 4 here!


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