Using GPIO pins on Raspberry Pi

The small size of the RasPi means that it lends itself very well to home automation projects. As my first step in understanding how hardware interfaces with the computer, I decided to follow the examples given at
drogon.net.

I got myself a nice starter kit from skypang.co.uk. The kit contains a plastic case for the RasPi along with a breadboard. The kit also contained connecting wires, 2 switches, a few LED lights and resistors.

My first crack at using the GPIO pins on the Raspi was with implementing tuxx crossing. As soon as I set up the first LED, I realised I could recycle some of the components from Siddharth's broken toys. There was a sword which we bought for haloween about 2 years ago. It had a speaker built in which made the sound of clashing swords as the press of a button. In the last play fight Siddharth had with the sword, the plastic blade had snapped and the sword had lost all interest for Siddharth. The speakers I extracted from the sword turned out to be suitable for use with the RasPi.

The project consists of an executable which can set/unset a pin or also read from it. This was used in conjunction with a shell script to write a Traffic Crossing system.

Here is the system in action.

The speakers are a nice touch and the entire system now mimics a Pelican Crossing quiet accurately.

Building kernel modules on the Raspberry Pi

To enable wireless on my RaPi, I bought a Edimax wireless usb dongle. This is based on the Realtek chipset which unfortunately was not supported out of the box on the 2012-06-18-wheezy-beta image I was running.

I was following the instructions posted here to enable the wireless dongle but soon found that the binary driver posted doesn't match the kernel version(3.1.9+ #144) I was running on my RaPi.  This meant that I had to build the kernel module required to run the wireless USB dongle from sources. The kernel headers for the running kernel are not provided in the Debian repository or the Rapi firmware git repository. Instead, the kernel sources used to build the kernel have to be used to setup the build environment.

Given below are instructions to build the kernel module for the latest development kernel on the Rapi as well as cross compile on a Linux based laptop or desktop. The limited resources on the RaPi means that building the kernel on the RaPi will take a long time. For this reason, I recommend that you cross compile on your desktop and then copy over the results to the RaPi.

Building on the RaPi.

1) Install git. Also make sure gcc and make are available on your Rapi.

# apt-get update
# apt-get install git make gcc

2) Clone the RaPi kernel git repository

# git clone --branch rpi-patches --depth 1 https://github.com/raspberrypi/linux.git rapi-linux

In my case, I cloned the branch on another machine and copied the resulting directory rapi-linux over to the RaPi at the location /root/rapi-linux.

3) Create a symlink to the kernel build directory used by the build process

# cd /lib/modules/3.1.9+/
# ln -s /root/rapi-linux/ build

4) Copy over the config file and prepare the sources

# cd /root/rapi-linux
# make mrproper
# zcat /proc/config.gz > .config
# make oldconfig
# make modules_prepare

You can build your kernel module at this stage but will find that the build complains about Module.symvers being missing. Attempting to load the resulting module fails with the error "Error: could not insert module ./8192cu.ko: Invalid module format" and the following line in dmesg "no symbol version for module_layout".

To complete the build environment, you will have to generate a Module.symvers file by building a kernel. To do this, run the command

# make vmlinux


This will take some time to build.


To build the module on the RaPi, simply change in to the module sources directory and run

# make -C /lib/modules/`uname -r`/build/ M=`pwd`


OR

Cross-compiling on a x86 based environment.

If you have a Linux based system, you could cross compile on your laptop and copy the result to the Rapi.

The following commands work for Fedora. You will need to adjust to get it working for your distribution


1) Install git, gcc, make and  gcc-arm-linux-gnu required to cross compile the kernel


# yum install -y git make gcc  gcc-arm-linux-gnu

2) Clone the RaPi kernel git repository

# git clone --branch rpi-patches --depth 1 https://github.com/raspberrypi/linux.git rapi-linux

3) Copy over the config file from the RaPi and prepare the sources

On the RaPi
# zcat /proc/config.gz > /tmp/config


Copy over /tmp/config on the RaPi to your own system. Now copy it over to the git repo you just cloned.


On the Laptop/Desktop
# cd rapi-linux
# cp /tmp/config .config
# make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnu- oldconfig
# make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnu- vmlinux

At this point, your build environment is complete.


To build a module on the linux desktop, change into the module sources and run

make ARCH=arm CROSS_COMPILE=/usr/bin/arm-linux-gnu- -C ../rapi-linux/ M=`pwd`

Replace ../rapi-linux/ with the location to your own RaPi kernel sources.

References;
http://elinux.org/RPi_Kernel_Compilation

Chicken Salan

Salan is term used to describe a creamy curry. This recipe is currently my favourite Chicken curry recipe.

I first came across this recipe on Youtube. I have deviated from the original recipe by adding a tbsp of yoghurt to the curry while cooking it.

Ingredients

•  Chicken preferably on bone without any skin. I prefer using the 825 gms of Tesco's Free Range Corn Fed Chicken drumstick and thighs
• 2 medium onions, finely chopped
• 8 cloves garlic, finely chopped
• 2 inch piece of root ginger, finely chopped
• 2-4 green finger chillies, finely chopped
• 1 tsp tomato purée
• 1 tbsp coriander powder
• 0.5 tbsp cumin powder
• 1 tsp turmeric powder
• 1 tsp cumin seeds
• 1 tsp Garam masala
• 1 tbsp yoghurt
• 3 tbsp olive oil
• Fresh coriander leaves for garnishing.
• Salt to taste

Method

• Add the oil to a sauce pan and throw in the chopped onions. Mix them thoroughly and cover with a lid. Fry until the onions are dark brown.
• Add a cup of water, mix and let it boil for about 3 minutes.
• Add the dry spices, salt, garlic, ginger and chillies followed by the Chicken. Mix thoroughly, cover and let it cook for about 5 minutes.
• Add the yoghurt and the tomato purée. Replace the lid and cook for a further 7 minutes until the chicken is cooked.
• Switch off the heat and add the coriander leaves.
• Let it rest for about 5 minutes. 

Serve with bread, rice or rotis.

Palak Paneer

My mom was always concerned with my younger brother's diet after he developed patches on his skin which the doctor blamed on vitamin deficiency. She learnt of this recipe to make spinach, called Palak in Hindi,  from our Punjabi neighbors and she hoped he would like it. My brother never developed a liking for spinach, but I ended up loving it.

This dish is very popular in British Indian Restaurants where it is sold as Saag Paneer. They tend to use finely chopped spinach here instead of puréed spinach which I like to use. I have always associated Palak Paneer with puréed spinach and that is how I like it.

In this version I use Indian cottage cheese called Paneer. This is the usual cottage cheese which has been strained through muslin and cut into blocks. These are available in 200 gm packs at Tescos. I tend to use only half of it and freeze the rest to use at a later date. You could substitute it with peeled and boiled chunks of potatoes instead.

Ingredients

• 500 grams of Spinach washed with the stems removed
• 1 medium onion - chopped coarsely
• 4 cloves of garlic 
• 1 inch piece of ginger
• 2 finger green chilies 
• 2 Tomatoes - quartered
• Paneer - Indian Cottage Cheese - cut into chunks
• Vegetable oil - 2 tbsps
• Salt to taste

Method

• Wash the spinach and let the water drain away. Transfer this to a saucepan, add a bit of salt and start the heat. The water on the leaf as a result of washing should be sufficient for boiling it. If you see the leaves burning, sprinkle a bit of water on them. The salt helps preserve the green colour. Do not cover the sauce pan. The leaves will shrivel down to a tiny fraction of the volume you started out with. Switch the heat off and leave it to cool. Once cooled, puree the spinach in a blender.
• In another blender vessel add onions, garlic, ginger and the chilies and blend until you have a smooth paste.
• Heat a sauce pan and add two tablespoons of oil to it.
• Add the paste made earlier and fry until the raw taste of onion is no longer present. If the paste starts burning add a bit of water to it.
• Add the quartered chunks of tomato to the pan and fry for a minute.
• Add the pureed spinach, cover the pan and let it cook for about 5 minutes.
• Add the chunks of paneer, cover the sauce pan and let it cook for another 3 minutes.
• Once done, switch the heat off and let it rest for a few minutes.

Serve with rice or rotis.

Portugese Sea Food Rice

A while back, Shyja  along with some colleagues were invited home by Portuguese friends for lunch. One of the highlights was a sea food rice which Shyja could not stop raving about. She kept pestering me to cook something similar. So after a few searches on Google followed by some calls to her friend, I have the following recipe.

The recipe is based on the recipe listed here along with a few tips from Shyja's friend.

The recipe calls for a variety of rice used in Portugal. Basmati will not do for this dish since the final form is rice in a broth. Basmati will I suspect turn into squishy mass in such a case. Since I couldn't get my hands on the exact variety of Portuguese rice, I had to settle on Spanish Paella rice instead. This in my opinion is a very good substitution.

Ingredients

• 1 onion - chopped fine
• 4 cloves of garlic - chopped fine
• 2/3rds of a can of peeled plum tomatoes
• 1 capsicum
• 1 400g pack frozen raw "Fruits de Mer" - this includes prawns, mussels, scallops, squid, etc
• Paella rice - I used a 300 ml cup and filled it to the brim with rice. This serves 4-5
• 2 cubes of Maggi chicken cubes
• 4-5 crab sticks
• Fresh coriander for garnishing
• 1 tablespoon oil - I used olive oil
• Salt to taste

Method

• Add 1 tablespoon Oil to the saucepan. 
• Add chopped onion and garlic and fry till transparent. Add the chopped capsicum and cook for about 30 seconds.
• Add 2/3rds of the tin of peeled plum tomatoes and cook till some of the tanginess of the tomatoes is gone.
• Add washed Paella rice to the saucepan and mix well.
• Add 3 cups of water to the saucepan. The volume of water should  be 3 times the volume of rice. Top up the water in case you have a danger of it getting dry.
• Add the 2 cubes of Chicken stock to the cooking rice.
• When the rice is halfway done, throw in the sea food(fruits de mer) and let it cook until rice is done. This shouldn't be longer then 7-8 mins.
• When the rice is done, switch off the heat. The result should be rice in a very watery broth.
• Add the crab sticks and mix.
• Sprinkle fresh coriander on top.

Chicken Biryani - Kerala style

There are many variations to Biryani. The 2 most famous ones are the Hyderabadi Biryani where the rice and meat are cooked together and the Lucknowi Biryani where the rice and meat are partly cooked separately, laid out in layers and finally cooked under pressure.

My favourite version however is the one from down south in Kerala.
Prawn Biryani at OneIndia
I came across the recipe when searching for prawns biryani. The interesting twist in this version of the biryani is that the rice is cooked in diluted coconut milk. This gives it a very nice flavour.

This is a very easy recipe where you only require one large vessel to cook it in. In my case, I use a pressure cooker. If you do not have a pressure cooker, you could use a vessel with a lid instead.

For the coconut milk, I use Maggi Coconut milk powder. I also use Shaan Bombay Biryani spice mix. You could use other brands of biryani spice mix instead. This biryani masala contains chilly powder which makes it hot enough for me. In case your spice mix doesn't contain chilly powder or you like it hotter, you could add Red Chilly powder just before you add the tomatoes.

Ingredients

• Chicken - I use thigh pieces.
• 1 Onion - Chopped
• 2 Tomatoes - Chopped
• Few mint leaves
• Handful of fresh coriander
• Ginger Garlic Paste
• Turmeric powder
• Basmati Rice - This depends on the number of people you cook for.
• Whole Spices
• 4 Green cardamom
• 2 Black cardamom
• 1 Stick cinnamon
• 2 Star Anise
• 4 Cloves
• 2 Bay leaves

Method

• Soak the Basmati Rice for about 10 minutes. Do not keep it in water for longer then 10 minutes or the results would be squishy Biryani.
• Heat oil in a pressure cooker base and add the whole spices to it.
• Add chopped onion and let it fry until the onions are brown.
• Add the chopped tomatoes to this mixture and cook till the tomatoes break down.
• Add mint and coriander leaves and fry for another minute.
• Add Chicken followed by the Biryani Spice mix. Mix the contents thoroughly.
• You now need to add water diluted with coconut milk. It is very important to get this right. The rough guide is to add slight less then twice the amount of rice in terms of volume. This is because chicken leaves a lot of water while cooking. So if you use 3 cups of rice, I would use 5 1/2 cups of water with coconut milk. Mix the contents thoroughly  making sure you don't have anything sticking to the bottom.
• Close the pressure cooker lid and let it cook until it lets out steam twice. In case you are not using a pressure cooker, let it cook till the water is completely soaked.
• Switch the gas off and let it cool down slightly. In case you use the pressure cooker, take it off the stove and let it cool until the pressure is sufficiently low so that you can open the lid without any difficulty.
• Serve with Raita.

Ealing Road Temple, London

Pictures from the Ealing Road Temple. The carvings on the outside were very nice. They would not let me take pictures of the interiors which was also very nice.

Even though there weren't too many people at the temple, there was temporary barriers set which took you around the temple. It felt more like an exhibition and less like a temple. This could have been setup because of the Janmashthami celebrations recently.

The security and the notices which includes gems like 'You are responsible for your own safety in the temple.' just put me off.

If you are looking for good vegetarian food, the restaurants outside the temple were very good. We had the Special Gujrati thali at a place called Dadima and it was very very good.

Ealing Road Temple