Author Archives: garreth

Arduino Variable Types Explained

Here’s something for reference.
I can never find just quite the succinct reference to Arduino Variable types. Nowhere could i find a list of minimum and maximum values, the bits, and the memory used by each variable type.

Neither was there any clear definition of meaning of ‘unsigned’, which just means no plus or minus signs in this type – that is all numbers positive. This increases the highest number that can be stored in the same memory. (thank me in the comments).

Usage Variable type Bits Min value Max value Ram usage Comments
common boolean 8 TRUE FALSE 1 byte
common byte 8 0 255 1 byte
char 8 -128 127 1 byte  A single ‘character’ e.g. ‘a’ is a single char.  Represented by chr(65) or the binary: 01000001
word 16 0 65535 2 byte
common int 16 -32768 32767 2 byte
unsigned long 32 0 4,294,967,295 4 byte
common long 32 -2,147,483,648 2,147,483,647 4 byte
common float 32 -3.4028235E+38 3.4028235E+38 4 byte
The below types are only included for compatibility or further study.
redundant unsigned char 8 0 255  1 byte use byte instead
redundant unsigned int 16 0 65535  2 bytes use word instead
redundant double 32 -3.4028235E+38  3.4028235E+38  4 bytes use float instead
The below types are special types (see
special string variable  1 byte + x An array of chars
(used for storing strings to modify)
special enum variable  N/A Like boolean but custom fixed set of values allowed instead of TRUE/FALSE.
special struct variable  N/A Public sub variables
(as if you’d made a public class)
special pointer  N/A I’ll be honest, I wasn’t sure the use of this one. Here for completeness though!
Remark: “Unsigned” means no negative sign. This increases the range of positive numbers available.
Remark: Unsigned variables that exceed their capacity roll over back to zero. This could be useful to iterate through arrays of limited length

PPS If anyone can figure out how to properly format this table so it looks nice, with ‘center’ aligned text, please let me know wordpress was being frustrating!

(The formatting css is in the source, see the table tag)

Find Windows workstation logon script

This is a super quick tip from an online forum…
[ Where is the location for the windows logon script?]

If you’re looking for the location of the active logon script in a Windows domain network on a workstation, or just to figure out which logon script is being used for a workstation

TLDR; ‘Get to the point, where is the bleeding thing?!’:

To find the location of a user’s logon script, while logged in as the user, run the command:
net user “%USERNAME%” | find “Logon script”
or for a domain user,
net user “%USERNAME%” /domain | find “Logon script”

Standard location

The logon scripts themselves can be found on the network in the standard domain network share location:


Additionally, the commands:

net user “%USERNAME%” /domain


gpresult /r

Give interesting results for the current user and what Group policy rules are active for the currently logged in user/(machine?) respectively.

Obviously this is only relevant to windows computers in active directory with primary domain controller and group policy ordaining that each machine should run a logon script.


Search Terms:

Things i searched for in order to try and find this out:

  • find out what logon script a computer is using
  • find path of logon script from workstation
  • find path of logon script from workstation registry

(I couldn’t find the registry location as it turns out!)

If this post helped you, or you have additional tips, please leave them in the comments!

Excel tip – adding two numbers where one is text

Just a quick tip as i couldn’t quickly find the answer in google.

If you have two cells of data and you want to add them when one might have text instead of a number, use the SUM function.

For instance

Class Section 1
Section 2
Robots 10,000 1,000 =sum(B2:C2)
Humans 9,000,000,000 n/a =sum(B3:C3)
Plants n/a n/a =sum(B4:C4)

I also searched for: sum two values if isnumeric, excel add two numbers if text only include the non text and excel add two numbers if text.

Three Mobile Hotspot MITM Attack?


Is three performing a Man In The Middle SSL attack/proxy on my mobile hotspot?

Loading paypal:


Well hello NSA & GCHQ lol.

Funnily enough after searching Google for this issue and then retrying I don’t get some asshat trying to proxy my SSL connection. Or if they are they have a ‘genuine’ root certificate from a valid CA.

Project Teaser


Heres a little something that has come about from a related project I have built (and need to test)

Maybe I’ll write up both projects together!

Relevant hashtags #RaspberryPi #HTML5  #WS2812b


An explanation more beautiful than my words could ever be:
Giving Is The Best Communication – Thai Mobile Ad…:

The World full of horrible injustices, life is cruel and unfair. Survival of the fittest is now survival of the richest.

And the worst thing?
It feels like you’re just too powerless, poor or insignificant against the size if it.

Starvation, Cancer, HIV, Natural disasters whatever.

Well the truth is there is something you can do to change the world.

And its cheap, and simple and should make someone smile.

Its called A Random Act Of Kindness or RAOK.

Just do one small thing to improve the life of a stranger.
See that a Girl sobbing? Go give her a tissue.
Give your elderly neighbour a Christmas card or invite him round for a cup of tea.
Hold the door open for someone.
Carry a lighter just in case someone asks for a light.
Give out free hugs (I did this once. It was hugely fun. I made sure I got all the people with the saddest expressions 😉 ).

Have a think. Be good to people, even if you don’t know them.

Leave a note that says ‘pass it on’

Now you may never know the difference that a small random act of kindness makes to that stranger. But this is not about fame or fortune, its about changing the world one small random act of kindness at a time.

My hot tip? Why just one RAOK?

Share the love.

And Dear stranger,
If you find this, pass it on, and have a brilliant week!
(I know my name is on here, but who I am doesn’t matter. Thank me by doing a RAOK and asking them to pass it on 😉 )


Just a super-quick post here.

If you’re looking for addons or plugins for Microsoft Outlook to help you organize your emails and extend the functionality of Outlook

(note Outlook is very extensible, as with all Microsoft Office applications you can write Visual Basic code for Applications to hook into it’s functions. Absaloutely fantastic for hacking excel as I have been doing for the last few weeks – my work needs to invest in a proper database program for sure *sigh*)

You’d do no better than looking here

Snapfiles Outlook Add-ons


They have addons that are useful – and unlike most of the sites on i’ve found so far – up to date and compatible with recent versions (2003+) of Outlook.

Hope this helps folks!


Rfduino Chip vs Thermometer

Well, I’ve now debugged a few issues with my scripts from my last post.
(made them a bit more fault tolerant and actually take notice of $? exit statuses) .
Recap: Temperhum (USB) -> Raspberry Pi -> Xively chart, now also
RFDuino (bluetooth wireless) -> Raspberry Pi -> Xively chart

Tip:  If you’re struggling with the bluetooth on linux giving rx timeout errors (check the syslog if it’s not in the console),
update the software with the following commands:

sudo apt-get update
sudo apt-get upgrade

The Rfduino has been sitting next to my usb Temperature and Humidity sensor for a few weeks collecting data.


RFDuino and Temperhum

Since it had been both collecting data for a few weeks and sending them to Xively / Pachube / Cosm, I had a quick look to see how closely the readings match.

Rfduino vs thermometerr

The graphs do show correlation, thank goodness, but it looks like the RFDuino’s temperature scale isn’t right. The RFDuino is only updating the graph once a minute whereas the Temperhum is 2x a minute.

I didn’t really expect great accuracy for the RFduino thermometer seeing as it’s measuring from the chip. But this would still be useful in some more basic cases.

I think next on the roadmap for the RFduino is connecting sensors/remote controls (it would be cool to attach my RelaySockets to this and control the 2 connected relays via bluetooth from my Pi and Android smartphone!


My Humidity and Temperature sensor

A Temperhum from PCSensor.

A great little bit of kit – once you work out the conversion values for the C++ USB/i2c/HID code that lets linux talk to the thing!

Getting Rfduino working with Linux


I ordered this nifty ‘RFduino’, an arduino-compatible device which was also my first ever kickstarter purchase over a year ago now.
However, when the device arrived, the company behind it seemed exclusively interested in the iPhone handset to the detriment of all other platforms.
Personally, the lock in monopolistic attitude of Apple and its customers really gets my goat, but I digress.

The lack of support and that the device arrived half a year late left me with a sour first taste of Kickstarter.

Since then, I’ve played with the Rfduino using JT’s iGear (no, I don’t know why fell into the Apple pit either) using the only app available to use the sketch it comes with – the internal thermometer

But that’s rather limiting!! I bought this device with plans to build a Wireless ‘Internet of Things’ sensor network for my house.

I have designs on talking to every platform available using protocols such as mqtt, backends like rrdtool and web interfaces for my housemates to see and control the action.

This is something I’ve been dreaming and sketching out  for years, because lets face it, who doesn’t think having the lights turn out when you leave is super cool?

So without further ado, how do we get the RFduino to talk to a linux machine, in my case a Raspberry Pi running Raspbian.



You will need

  • Internet connection to download tools
  • Bluetooth packages installed (bluez-tools)


Power on the  RFduino and linux machine. I used two Alkaline AA batteries to power the RFduino although Rechargeables do work.

Install the Bluetooth 4 usb adaptor on the linux machine
Install the necessary bluetooth programs:

sudo apt-get install bluetooth bluez bluez-utils bluez-firmware

(you may need to reboot the machine afterwards, I don’t believe I did)

Bring up the bluetooth interface:

sudo hciconfig hci0 up

Run a Low Energy scan to find the address of your RFduino:

sudo hcitool lescan

Should elicit results similar to this:
EA:BA:20:48:37:80 (unknown)
88:D8:CD:08:12:FA (unknown)
99:D8:CD:10:66:FA (unknown)
DD:AF:13:17:23:80 RFduino

Select and copy the MAC address given for the RFduino on your system.

(I have no idea why you have to scan as root, someone please leave a comment if you do, and if theres a way to run as a normal user…groups?)


Read the temperature attribute from the RFduino using gatttool. Paste your devices MAC address in instead of mine of course.

sudo gatttool –device=DD:AF:13:17:23:80 –interactive
[   ][DD:AF:13:17:23:80][LE]>
[   ][DD:AF:13:17:23:80][LE]> connect
[CON][DD:AF:13:17:23:80]][LE]>char-read-uuid 2221
handle: 0x000e value: 00 00 a8 41 00 00 00 00 00 00 00 00
[   ][DD:AF:13:17:23:80][LE]>quit

Now from that exchange with the RFduino, we have gained a long hexadecimal string.
From a post on the RFduino forum, I learned that the value we want is always after the ’00 00′ string (in bold above).
This is the temperature read from the RFduino’s internal sensor * 8.
So we need to convert this to Decimal and divide by eight to retrieve the temperature value in celsius (American readers, why aren’t you on SI units yet? :P).

Convert the hex value to decimal temperature

echo $decimal

The above method returns an integer value. This is because Bash has limitations working with numbers that are not whole (decimals).
Workarounds use the command bc to interpret string inputs as decimal numbers. I think there is a method to define variable types in bash, but I didn’t get very far with this.

My attitude is that once you start hitting the limitations of a shell scripting language, it’s time to migrate to a proper programming/interpreted language (at least python).
Spending hours and using multitudes of additional programs make it work is often pointless.

Just think, if you had to run the script on a embedded system without most of those commands, wouldn’t it just be better to do it in C++?


Next time:

Now that I’ve successfully read the values being sent by the RFDuino I need to figure out how to automate the process – in non-interactive mode.

These commands do the same thing but respond differently

sudo gatttool -b [MAC] –char-read  –handle=0x000e
Characteristic value/descriptor: 00 00 a8 41 00 00 00 00 00 00 00 00

sudo gatttool -b [MAC] –char-read –uuid=2221
handle: 0x000e   value: 00 00 a8 41 00 00 00 00 00 00 00 00

Simple bash script to read temperature in celsius (accuracy is lost here as the decimal is converted to an integer)

stringZ=$(gatttool -b [MAC] –char-read  –handle=0x000e)
echo $decimal

don’t forget:
chmod +x [whatever you called the script]

and run it as root:
sudo [whatever you called the script]


I won’t pretend to understand the naming conventions of Bluetooth 4.0/LE.
I don’t! I spent a whole day looking into it and could not find a single source that easily explained the structure, naming, and profiles. If someone has seen something good, please post in the comments!

It’s frustratingly close, like I can see there is a neat logic to it, but I just don’t care to spend any more time trying to figure it out, when all I want to do is use it. This does make it slightly more hacky and less neat and quick of course, but that’s life!



gattool commands to read the sensor:
Bluetooth Low Energy: Read-Write to Sensor Network from Raspberry Pi

howto convert hex to decimal on the command line:

howto do calculations on the command line:

Hacked up way of using gatttool non-interactively, using ncurses and a python script:

Bash string manipulation: