OK, just the easy one this late in the evening: timestamps.

You need the datetime module. At the top of the file add “import datetime”. There are three classes in that module, date (just a date, with no time), time (time of day, 00:00 to 23:59) and datetime (date and time combined for a unique instant in history). For a log which will run many days you want datetime. The datetime class has a now() function which gives you the equivalent of the VBA now but for a log which might run for many months I'd suggest using its sibling utcnow so you don't get funny things happening when the clocks change.

I haven't got a Pi or anything with GPIO so just the interesting bits:

#!/usr/bin/python

import datetime

# ....
temperature = 42.5       # Dummy

tfile = open("/home/pi/Desktop/tempdata.txt","w")
#writes the temperature data to the tempdata/txt file
tfile.write("%s: Temp C,%s" % (datetime.datetime.utcnow(), temperature) +'\n')
#closes the tempdata.txt file
tfile.close()

Apart from using my own user name for the directory (rather than 'pi') that runs as shown for me and produces:

2013-01-24 23:18:35.028279: Temp C,42.5

It's confusing having the datetime module containing a class with the same name. If that's the only class from the module you want to use then you can make it a bit more compact at the point of use. Replace the import statement with:

from datetime import datetime

then just use the class name directly:

tfile.write("%s: Temp C,%s" % (datetime.utcnow(), temperature) +'\n')

Thanks Ed

Going to be back on it in an hour or so, once I have that working I can then try a loop so that it logs every few seconds. That should be fun.

Posted By: SteamyTeaIs it possible to put the modprode w1-gpio and modprobe w1-therm commands into the Python script at the very begining?

Yes, use the subprocess.call function to run an external program. Easier, use subprocess.check_call to run the external program and check its return code is zero (i.e., it worked). In simple cases it just takes an array of strings as the parameter, one string for each “token“ in the command line.

from subprocess import check_call

check_call(["modprobe", "w1-gpio"])

This throws an exception for me because I haven't got that module installed (not having GPIO on my laptop). When I use it with a module I have got it works fine.

Posted By: SteamyTeaThe other thing is that when it writes to the tempdata.txt file a terminal window telling me that it all went alright opens up which has to be closed before I can read the file (or reload it). What is that about?

Sorry, no idea. How are you starting your program?

I am starting it from Geany, if I want to start if from the .py file, do I have to compile it first (whatever that does) and do I have to make it executable? Does either of them stop me editing it after?

Edit:

Just made the led file 'executable' and the terminal screen does not pop up now but the light keeps flashing

I had a little fiddle with it and could not get it to start, so that may be the problem.

There is a Python for the RPi called RPi.GPIO, I used to it make the led flash. Should I try loading that and setting pin 4 to read instead?

As far as I know I do need to be logged in as root.
At this point in time being root or not does not worry me as I am only playing, maybe later when I want to do some more serious stuff it may become important.

When I tried putting it in it just said there was an error at line 7. After a bit of playing about it was loading but then getting errors at various lines of the modprobe module. Maybe that is why they developed the RPi.GPIO. Shall have to look it up when I get back later.

Posted By: SteamyTeaWith this subprocess thingy I should be able to look at the w1/devices directory and get the unique ID for each sensor and somehow put that into my scrip as a variable so save having to manually edit the scrip each time I change a sensor. Is that and easy thing to do?

You could use a call to one of the functions in the subprocess module to run ls and look at its output as per your previous method. That'd be a rather perverse way to do it, though.

There are various ways of wandering around the file system in Python. Here are examples of two. I don't have a w1 directory in /sys/bus/ so these work higher up the tree from what you'd want.

>>> import os
>>> os.listdir('/sys/bus')
['platform', 'pci', 'rapidio', 'spi', 'i2c', 'eisa', 'MCA', 'acpi', 'pnp', 'scsi', 'mdio_bus', 'usb', 'serio', 'mmc', 'sdio', 'event_source', 'pci_express', 'isa', 'ssb', 'hid', 'pcmcia']
>>> import glob
>>> glob.glob('/sys/bus/*')
['/sys/bus/platform', '/sys/bus/pci', '/sys/bus/rapidio', '/sys/bus/spi', '/sys/bus/i2c', '/sys/bus/eisa', '/sys/bus/MCA', '/sys/bus/acpi', '/sys/bus/pnp', '/sys/bus/scsi', '/sys/bus/mdio_bus', '/sys/bus/usb', '/sys/bus/serio', '/sys/bus/mmc', '/sys/bus/sdio', '/sys/bus/event_source', '/sys/bus/pci_express', '/sys/bus/isa', '/sys/bus/ssb', '/sys/bus/hid', '/sys/bus/pcmcia']

I think with glob you could even do glob.glob("/sys/bus/w1/devices/28-*/w1_slave") to directly get the devices you need to access all of your temperature sensors, ignoring any other 1-wire devices on the bus(es).

:-)

But the books have already been written. The one I have to hand all the time is the O'Reilly book <i>Python in a Nutshell</i> by Alex Martelli. I'd thoroughly recommend it to anybody who wants to learn Python if they already know a few other languages.

For introductory programming books using Python, I know there are a few around but haven't looked at any so can't say anything useful. However, <i>Python for Kids</i> looks interesting. My 13-year old niece was talking about how some other girls in her class had been learning to program on Raspberry Pis and lamenting that access to computers you can do that sort of thing on is not like it used to be in schools. I just laughed at her. She has a fairly powerful desktop with a gorgeous widescreen monitor, an iPhone and an iPad all of which would be just fine for getting some programming experience. Might get her that book next time I go to visit. Might be a good book for adults, too.

http://boingboing.net/2012/12/18/python-for-kids-a-playful-int.html

Splendid piece on Woman's Hour last week, on R4, with a splendidly clued-up girl programming a Pi and some similar basic computer like there was no tomorrow. I think she could teach!

If you're struggling with you pie you'll soon be able to ask the kids for help -

15,000 Raspberry Pis for UK schools – thanks Google!

Today’s been a bit unlike most Tuesdays at the Raspberry Pi Foundation. Today we’ re the recipients of a very generous grant from Google Giving, which will provide 15,000 Ra spberry Pi Model Bs for schoolkids around the UK.

Yeah the 13-year geek-girl was great. More like that please.

As you've discovered steamy, the correct way to get modules loaded automatically is to put them in /etc/modules/

(and trying to load them in your python program, whilst possible, is definitely not right).

If you want to read 1-wire devices easily the simplest way is to install owfs. That will expose your devices over http (owserver) or as a virtual filesystem (owfs). There are also python bindings, so you can easily enumerate, read, configure. But you can of course do your own low-level access via the kernel interface, as you are doing, if you prefer.

If you've only got a few lines of code accessing the 1-wire bus then I don't see any compelling reason to use owfs. If you later expand it to something more complicated which you don't want to be dependent on the details of Pi GPIO (because you might want to port it to other systems) then owfs would give a useful level of abstraction. It'd probably also help if you wanted to have multiple processes accessing the 1-wire bus or wanted to get at the 1-wire bus across your network.

Yes, a Python binding is a library (typically written in C) which allows Python code to call some other library. On Ubuntu the Python binding for owlib is in the package python-ow (i.e., sudo apt-get install python-ow, other packages which might be helpful are owserver and ow-shell). Use with import ow. Had a little play but must admit I couldn't figure out how to enumerate the devices on the bus - but maybe that's because I don't any real 1-wire devices to hand so owserver is simulating a fake bus for me (which is kind of it).

Yes, you'd need to use w1-gpio as well. Owfs does its own access to all the normal serial port and USB 1-wire adapters (and having w1 modules loaded breaks things, IIRC) but for GPIO owfs delegates all the work to w1.

As I say, I'd ignore owfs for now and concentrate on getting interesting stuff done. But it's worth keeping in mind for later.

Raspberry Pi Announces $25 Camera Module

Technical details are blurry. The exact sensor size is unknown, but five megapixels is the likely size according to official comments on RPi forums. Makers won’t be able to change lenses, add physical filters, or even zoom, but the camera module will be capable of HD video capture. Proposed applications for the new module are focused on robotics, home automation, and aerial applications where potential crashes favor low-cost solutions. Priced at $25, it will cost the same as the newly released Model A board — much cheaper and easier to replace than an iPhone or DSLR should an airborne project inadvertently “zoom in” to a crash landing.

Not done anything interesting like that Triassic but I did just break down and buy one to replace my old HTPC. It's absolutely cracking, and cost less than the parts from my old machine will get on Ebay.