How to transfer data to PC

Hi, I’m new to Codea
I would like to write a simple program to collect a fair amount of accelerometer data and analyze the data on a PC using Excel or other tools.
Would someone point me to an example on how to collect data and more importantly how to transfer data to PC?

The easiest way is to save the data locally in the file format of your choice and then use one of several apps (both available for PC and Mac) like FunBox, or iExplore to connect your iPad to your computer, you then have to browse the app directory structure, find the Codea folder, inside that find the .codea folder and inside that you’ll find the local documents folder where 's data files are stored.

For later analysis on the PC using Excel, you might want to save your data as a CSV (each value separated by a comma) file.

Hope this helps.

Other, slightly more difficult alternatives:

  1. Jailbreak, then use normal unix copy commands - rsync is my favorite. This has the advantage of being able to be done untethered.

  2. Use http.request() and send your data to a website.

As for how to collect the data - go look at the example programs (if you haven’t already) to see how to get the acceleration data; I’d then simply accrue it in a table, or if you’re doing (2) above just post it on the fly (depending on how often you want to sample)

.@bortels could you be more detailed on how to send a file to a website? I have a web site, but i don’t know how to send a file to my site with codea, nor what to do on the sever side…

Heh - I knew someone would ask.

So - here’s a basic skeleton, the minimal amount you’d need to do; and you can build on it. This is running on my ubuntu box at home:

bortels@duo:/var/www/codea$ ls -al
total 16
drwxrwxr-x  2 bortels bortels 4096 Dec  6 10:13 .
drwxr-xr-x 46 bortels bortels 4096 Dec  6 10:11 ..
-rw-rw-rw-  1 bortels bortels   26 Dec  6 10:13 data.txt
-rwxrwxr-x  1 bortels bortels  489 Dec  6 10:12 index.cgi
bortels@duo:/var/www/codea$ cat index.cgi

use CGI qw(:standard);                                      
use CGI::Carp qw(warningsToBrowser fatalsToBrowser);       

print header;                                               
print start_html;                            
$d = param('data');
if ($d) { print "Data received.\
"; }
else    { print "no data"; }
open (F, ">>data.txt");
print F scalar(localtime) . ' ' . $d . "\
close F;

print end_html;

You will likely need to “touch data.txt ; chmod og+w data.txt” to set up the permissions on the data file.

You can hit this with a browser - go to to see the data, and you can hit to add data. Please keep it clean. :slight_smile:

In codea, http.get() the above URL(s), to either read data.txt or to add data.

In the case of the original post, you could sample your accelerometer data, and do http.get with data=results and it would go to the text file, which you could then import into a spreadsheet or such; change the print statements in the perl script to use a reasonable format.

I hope this makes sense - it’s as simple as I could make it, but I’ve been doing this for what, 20 years? so I don’t know what’s clear and what’s not. Ask questions if you want.

Ok… Btsdfg""& hsol snzuenp sksi? Snhuejso lmsp mmmpsjd! Hahaha! Gdbsu,a ghuigh?
Hem, that’s a little bit what your post sound like to me… (No offense, i’m just an uneducated moron…) what langage is it? 'ubuntu’means linux i guess? Any suggestion for people who know only javascript/html and run their web site on the ipad from textastic…?

Heh - yeah, the real problem is that the above assumes you have some passing familiarity with perl (the language it’s in), ubuntu (a linux operating system, although the above should work on basically anything but windows), and some basic sysadmin skills.

This is actually a fairly suitable situation for a site that was in another thread - take a look at for a semi-complex example (but at least it’s in lua!). Modifying this to collect data, and spit it all back out, should be straightforward, and for temporary non-giant amounts of data, you’ll be able to use their free usage tier.

If that’s still greek, maybe I’ll try to work up the same thing I did above, but on as an example.

So here’s a very lame first crack using

d =
if (d) then
	 return d, {["Content-Type"]="text/plain"}
	 return "Boo!", {["Content-Type"]="text/plain"}

You can go there, make a new script, paste this in, then use the link they give you - for example, mine is to log “monkey”. You as the owner can then look at the logs.

You could also do things like save the data to persistent storage, and have a different URL in the same domain spit back out a csv file of the data or such. Again - look at the leaderboard for examples of both saving data and spitting out custom results.

Thanks for all this interesting info @bortels. I had a look at webscript link: the code is nice and simple, but i have not got the big picture of what they do: they sell and/or we have to pay an account to use their code? And this is LUA, but is not installed in codea, is it?
I’ll take the time to look at your examples and will do some experiments. Thanks.

They sell it (it’s what they call PaaS, Platform as a Service), with a free tier; in a nutshell, you can do what you want for free, but they nuke it after a week. For $5 a month, they’ll not nuke it. I don’t think it’s a great business model, but they seem to like it, and if you don’t want to get deep into server-side stuff, it does fit the bill.

There are other ways to get free server-side code - run your own box like I do, or use google appscript or redhat’s new openshift stuff (google for them) - but they tend to be more complex. (I actually really like openshift - it hits the sweet spot between ease and power, and it’s what I’d use if I didn’t have a server already)

And yes - that lua code is running on their servers, in response to what your lua code does.

Ok, thanks.

Does anyone know how to decode a PNG image file. I’m able to pack data into an image on the iPad, save it in Dropbox, sync Dropbox with my PC and see the file with a .PNG extension on my PC. If I dump the file with a hex editor, I can find the different chunks of information, but I haven’t found anything that says how to decode the actual RGB information. I know the information in the file is correct on my PC. I checked this by loading the PNG file into a photo editor and increased the size of the image until each pixel was a square. I then took the eye dropper to display the RGB values of each pixel. If I start at the lower left pixel of the image and move up then repeat, each pixels RGB value is the value I packed in the image. If I can decode the PNG image, then I can create the file on the PC.

Thank you all for the suggestions.
As a beginner I’ll try TechDojo’s method first. :slight_smile:

Continuing from above. Actually, if I save the PNG file as a RAW file using a photo editor, the RAW file has the RGB values for each pixel as individual bytes. The RAW file just needs to be rearranged to match the original file.

Continuing my post from above, if I create the image file in the correct order for the RAW file on the PC, then there won’t be any reason to convert it at all. The steps would be, create the file as an image on the iPad, save it in Dropbox, sync Dropbox with the PC, load the PNG file into a photo editor, save it as a RAW file, and the RAW file should be the original file on the iPad. The only goofy process will be using the photo editor to convert the file. Sounds good in theory, I’ll have to wait and see if it actually works.

Continuing again from above. Everything worked out just fine. I was able to create the .PNG file so that the .RAW file being created was in the correct order. No converting of the RAW file on the PC was necessary. The .RAW file can be renamed to .txt or .bin depending on the type. So far, the program will create an ASCII file that’s terminated with HEX zeroes, or a HEX file with the file length as the first 3 bytes of the file. To test, I created an ASCII file of random values separated with commas that I imported into Excel without any problems. I’m still cleaning up the program and testing it, but so far everything looks OK. As I said above, the only goofy part is using a photo editor to convert the .PNG file to a .RAW file. But I guess that’s no more goofy than having to hook the iPad up to the PC and using a program to find the file on the iPad. So far the steps are, create a table/string of the info you want, pass the string into my program that creates a .PNG file in Dropbox, sync Dropbox with the PC, load the .PNG file into a photo editor, save the file as .RAW and rename the file and extension if necessary.

@thirtyeight If you’re still looking on how to save acceleration information in a table and to load it into Excel, this might help you. See my other post “Send file to a PC” for more details on what you need to do. As for saving acceleration data, change the interval for how often you want to read data, and change sample for the number of samples you want. In this example, it’s set up for a sample every 1/2 second and it will get 10 samples. So you will get 5 seconds of information. If this isn’t what you want, maybe it will give you an idea.

EDIT: I had an error in the table.insert lines, it’s been fixed.

function setup()
    -- 10 samples at 1/2 second intervals,  5 seconds run time
    interval=.5    -- interval in seconds
    samples=10     -- number of samples

function draw()
    if samples>0 then
        if (ElapsedTime - et) > interval then
            samples = samples - 1
    if samples==0 then

-- this function is all that's needed to create the .png image file

function createPNG(strng)    -- pass a string or table of information
    local fileName="Dropbox:CodeaFile"    -- file name for .png file
    local img1,size 
    local count=0
    local x,y,v1,v2,v3,s1,s2,b1,b2,b3,z
    local a1=256; local a2=256*256
    local ascii=true
    if type(strng)=="table" then
        strng=table.concat(strng)    -- convert a table to a string
    -- check for all ascii or a mix of ascii and hex
    for z=1,size do
        if x<32 or x>126 then    -- non ascii value
    -- calculate width and height for image size and create img1
    -- calculate 3 byte size (b1+b2*256+b3*256*256) for hex file
    b1=size; b2=0; b3=0 
    if b1>=a2 then
    if b1>=a1 then
    -- move string data into r,g,b values and set x,y point of img1
    for y=s2,1,-1 do   
        for x=1,s1 do
            if x==1 and y==s2 and not ascii then
                img1:set(1,s2,b1,b2,b3,255)    -- put size in 1st rgb entry of a hex file             
                count = count + 1
                if count<=size then
                    count = count + 1
                    if count<=size then
                        count = count + 1
                        if count<=size then
                    img1:set(x,y,v1,v2,v3,255)    --save rgb values per x,y point
                    img1:set(x,y,0,0,0,255)    -- fill remaining image with 0's

Two suggestions:
Save your file in the documents: directory instead of DropBox:. I don’t think the DropBox for has a bidirectional sync.
Create a class that is a vec3 and assign the acceleration data to a class instance, and store that in the table. Makes it easier to manage the data both from a read and write perspective.

Hi @aciolino The Documents directory doesn’t have a sync option, so saving the file there won’t help to sync it with the PC. Also, saving the data as a vec3 probably won’t help any either because the .png file is just a stream of bytes. It might save table space on the iPad, but in the .png file each RGB value is just a byte of data. You’re correct about the bidirectional sync. That takes care of writing code to send a file from the PC to the iPad using Dropbox sync.

OIC, I thought that the user was saving it to the iPad and trying to sync to the dropbox system to get it to the PC. That’s what I’m doing with my DropBox library, but it’s not what was being requested.