Category Archives: Linux

Below I will outline how to automatically log into your Raspberry Pi from a Windows PC using Putty. This requires the setup of SSH keys, which is very easy to do.

1. Create SSH keys.
Download Puttygen from here and run it.
Once open, click on Generate and move your mouse around to generate your SSH keys. puttygen2

2. Copy and past the public key, which is shown at the top of Puttygen into notepad, we will use this later.

notepadkey

3. Now click Save Private Key and save the key to your local drive

puttygen4 If you getting a warning about saving the key without a passprase, just click yes. puttygen3

4. log into your Raspberry Pi and create the authorization file,

pi@raspberrypi ~ $sudo nano /home/pi/.ssh/authorized_keys

5. Copy in the text we placed into notepad earlier. If you already have a key in there, just paste the new one onto a new line. Then ALT-X to exit and save.

putty2

6. Open up Putty and add in the IP address for your Raspberry Pi and make sure that SSH is selected.

putty1

7. Within Putty, on the left hand side, expand connection and SSH and select Auth. In the path for Private Key for authentication select the the private key we saved earlier. putty3

8. We now need to add the user name to log in with.
On the left hand side, select connection and then Data.
Enter pi as the username.
putty4

9. Go back to the main screen and save the session.

10. Now select Open to log into your Rasspberry Pi automatically. No need to enter username or password. The first time you log in you will be asked to accept the key.

Balancing Robot, Linux, Raspberry Pi

Guide to interfacing a Gyro and Accelerometer with a Raspberry Pi

April 29, 2013 Mark Williams 108 Comments

A lot of people have asked how I got the readings from the Gyro, Accelerometer, and Compass inertial measurement unit(IMU) which is used to keep PiBBOT upright.

UPDATED And updated guide has been published here, with cleaner and simpler code.

In this guide I will explain how to get readings from the IMU and convert these raw readings into usable angles. I will also show how to read some of the information in the datasheets for these devices. The theory and principals below can be applied to any digital IMU, just some minor modifications need to be made. Eg register values, sensitivity level...

The code can be found here;
https://github.com/mwilliams03/Raspberry-Gyro-Acc

A note about Gyros and Accelerometers

When using the IMU to calculate angles, readings from both the gyro and accelerometer are needed, which are then combined. This is because using either on their own will result in inaccurate readings.

Here is why;
Gyros - A gyro measures the rate of rotation, which has to be tracked over time to calculate the current angle. This tracking causes the gyro to drift. However, gyros are good at measuring quick sharp movements.

Accelerometers - Accelerometers are used to sense both static (e.g. gravity) and dynamic (e.g. sudden starts/stops) acceleration. They don’t need to be tracked like a gyro and can measure the current angle at any given time. Accelerometers however are very noisy and are only useful for tracking angles over a long period of time.

Here is an excellent tutorial about accelerometers and gyros;
http://www.instructables.com/id/Accelerometer-Gyro-Tutorial/?ALLSTEPS

Setting up the IMU and I2C

The IMU I use is a MinIMU-9 v2 Gyro, Accelerometer, and Compass which uses a L3GD20 3-axis gyroscope and a LSM303DLHC 3-axis accelerometer and 3-axis magnetometer.
The datasheets are needed if you want to use these devices;
L3GD20 datasheet
LSM303DLHC datasheet

This IMU communicates via the I2C interface.

From the images below, you can see how to connect it to the Raspberry Pi. You can also see the orientation of the X, Y and Z axis.

Continue reading Guide to interfacing a Gyro and Accelerometer with a Raspberry Pi →

Balancing Robot, Linux, Raspberry Pi, Uncategorized

Expand the Number of GPIO Pins on the Raspberry PI

April 25, 2013 Mark Williams 14 Comments

As of revision 2 boards, there is space to add some header pins to get access to eight more GPIO pins. These are found on the Header 5. Highlighted below.

Here are their functions;

P5-Pin1 - 5v0
P5-Pin2 - 3.3v
P5-Pin3 - GPIO28
P5-Pin4 - GPIO30
P5-Pin5 - GPIO29
P5-Pin6 - GPIO31
P5-Pin7 - GND
P5-Pin8 - GND

I needed some more pins for PiBBOT as I want to change my TFT to a character OLED which needed more pins then I had spare, so I decided to make use of these extra pins.

Here are the results, I soldered the head onto the underside of the Pi so I could plug in an IDC cable.

Continue reading Expand the Number of GPIO Pins on the Raspberry PI →

Balancing Robot, Linux, Raspberry Pi

Success with a Balancing Robot using a Raspberry Pi

April 18, 2013 Mark Williams 36 Comments

I have had success with getting PiBBOT to balance.

When I saw my first two wheel balancing robot I was very fascinated. And after receiving my Raspberry Pi, I decided to build one myself.
PiBBOT (Pi Balancing roBOT) is my first successful balancing robot. And it has room for improvement and extra functionality.

When building PiBBOT, I had a few roadblocks I needed to overcome;

I originally had the Anker as the power source for both Pi and the motors, however the amperage was too low.
Original H-Bridge not powerful enough for my motors
Gyro calculation off by 15 degrees

The TFT displays the angles from the accelerometer, gyro, complementary filter and power to the motors.
The buttons are to turn the motors on and off and to reset the gyro.

What next?

Incorporate the wheel encoders for better balance
Build a sturdier frame
Implement direction control
The able to self right itself after falling over
Room mapping
Retrieve a can of beer from the fridge

PiBBOT consists of these components;
Adafruit:
TFT; 2.2" 18-bit color TFT LCD display
RF Receiver :RF M4 Receiver - 315MHz

Pololu;
Motors; 9.7:1 Metal Gearmotor 25Dx48L mm with 48 CPR Encoder
Wheels; Pololu Wheel 90x10mm
IMU; MinIMU-9 v2 Gyro, Accelerometer, and Compass (L3GD20 and LSM303DLHC).

Anker;
Battery; Anker® Astro3 10000mAh 5V / 9V / 12V 2A Dual USB Output External Battery

Tenergy;
Battery; 7.2V Tenergy 3800mAh Flat NiMH High Power
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Continue reading Success with a Balancing Robot using a Raspberry Pi →

Linux, Raspberry Pi

Raspberry Pi with a 1.8″ TFT shield

April 17, 2013 Mark Williams 1 Comment

I'm using a shield from Texy to attach my TFT to my Pi.

This is soooo much easier then connecting up the cables individually, which requires me to always refer to the wiring diagram... and it always takes me two or three goes to get it right.

This just requires a quick snap onto the top of the GPIO pins. It also includes wiring to use 3 buttons on the GPIO pins not being used by the TFT.

Look here to find out where you can get one;
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=59&t=40674

Continue reading Raspberry Pi with a 1.8″ TFT shield →

Linux, Raspberry Pi

Automatic login between two Raspberry Pi hosts

March 22, 2013 Mark Williams Leave a comment

If you have multiple Raspberry's or even multiple Unix hosts , you will start to get frustrated at constantly having to enter a password every time you copy files between them or access these devices from another Unix host.

There is an easy way to disable this with RSA key pairs.

On each host, enter ssh-keygen
Hit enter to keep the default directory.
Passphrase. Leave blank and hit enter
Your keys are created under .ssh/

Now you need to copy over your key to all the other hosts with;
ssh-copy-id -i .ssh/id_rsa.pub username@serverip

Once this is done, you should now be able to copy files or access each device without having to use passwords.

You still need to enter a password when trying to connect from a host that hasn't got a key.

Continue reading Automatic login between two Raspberry Pi hosts →

Linux, Raspberry Pi

Raspberry Pi with a 2.2″ TFT

March 18, 2013 Mark Williams 3 Comments

Notro has done some great work with developing drivers for different models of TFT displays for the Pi.
He successfully created one for the Adafruit 2.2" TFT . This is a great little display and is very clear.

Notro's Wiki with instructions can be found here.

As with the 1.8" TFT from Adafruit, this device can be used to display video, images and your own data with easily using pygame.

A couple of images from my Pi running the 2.2 TFT;

Continue reading Raspberry Pi with a 2.2″ TFT →

Balancing Robot, Linux, Raspberry Pi

PiBBot – Robotic Project – Phase 2 – Prototype

March 8, 2013 Mark Williams 5 Comments

Here is my first attempt at getting PiBBot balanced.

This is a very early prototype, confirming that all the hardware works and the I can get the time of the main loop down to 20ms, which was easy.
This prototype also helped me get my head around the code and math need to balance.

I am waiting on the delivery of some hardware to build my final and larger version. Which will have a battery pack placed up high, this will help a lot with the balancing.

The main components used to balance this prototype;

MinIMU-9 v2 Gyro, Accelerometer, and Compass (L3GD20 and LSM303DLHC Carrier)
Solarbotics GM6 120:1 Mini Gear Motor Offset Output
Dual H-Bridge Motor Driver
315MHz RF M4 Receiver
12v battery

The receiver allowed my to change the PID values in real time.

There is also a lot of other components on the breadboard, but they are not needed to balance. Eg TFT, 8x8Matrix, Temp monitor...

Continue reading PiBBot – Robotic Project – Phase 2 – Prototype →