Friday, November 13, 2015

Hacking a Logitech MK220 wireless keyboard and mouse combo for a community computer

Recently during my stint as a Teach For India Fellow, I have been building Community Computers for use at my school. These involve creating an easy to carry box with projector, computer, speakers and wirless keyboard/mouse all stuffed in. After building one based around Intel NUC PC I decided to think of ways of decreasing cost of the Community Computers and make it more user friendly for our not so tech savvy teachers. Towards that, I thought of using an old non-HDMI VGA projector paired with a Single Board Computer APC 8750 which runs Android OS and has a VGA video output which makes pairing with an old projector possible..

If you think about it, a computer that runs Android would be more successful with teachers as compared to a Windows based PC. Teachers now days have access to smart phone so that are already comfortable with using Android. If you install appropriate apps on an Android based community computer, they can play all kind of content - videos, photos, PDFs etc. Also Android based SBCs boot fast and you don't really have to worry about viruses.

The APC 8750 supports playing of Videos and Photos from a USB flash drive that you plug into it. Here is what the result looked like:

If you notice, there is a small box with colored switches next to the wireless mouse. That box is actually a full fledged wireless keyboard hacked down to retain just the 4 arrow keys along with Esc, Space bar and Enter keys - because those are the only keys that you need to operate the Android OS on APC 8720 for playing videos and photos. It has proven to be a good idea because carrying a cumbersome keyboard to class when you only want to show videos and photos is not such a good idea. Big keyboards are prone to damage in a chaotic classrooms.

Here is how I went about hacking the Logitech MK220 wireless keyboard and mouse:

Step 1: Open up the keyboard and separate out the parts:
You can see the back side of the transmitter circuit and key membrane

Keyboard membrane (the one with silver traces on it), pressure pads sheet (made of rubber) and the transmitter.
Step 2: The membrane separates into two sheets - Top and Bottom. So the next step was to scan the sheet so as to highlight the traces for the keys that I wanted on my compact new remote. Since the length of the membrane sheets was more than what would fit in my A4 sized scanner, I had to perform the scan twice from both ends of the membranes and join the two images. While scanning the two images, I placed a black folder as their background to ensure that there was contrast between the traces of the membrane and the background which would otherwise have been white due to the white sheet usually stuck on glass facing side of the scanner lid.

Two sheets of the membrane lying on top of each other

Black folder providing contrast while scanning

Scanning in progress

Scanned the membranes from one side...

... and then from the other side because they did not fit all together at once in the scanner
Step 3: Next, I used Microsoft Paint to join the images. Then I used IrfanView to decrease their color depth to 2 colors (black and white) and then back to 16 million colors. This ensured that the contrast for the image had been maximized (each pixel was either white or black) and that I could now use the paint bucket tool of Microsoft Paint to trace the tracks on the images. The tracks were white and the background was black,

Decreasing the color depth (IrfanView) and then increasing it again (Microsoft Paint

Joined image. Decreased to depth of 2 colors only.
Step 4: Finally use the paint bucket tool to trace the tracks to the pads of keys of interest on the top as well as the bottom layer of the membrane. Then match the connecting pins to the pads on the keyboard transmitter PCB and make a list of what to pads on the transmitter PCB correspond to pressing of which key.

Step 5: Finally mount tactile switches on a PCB and assemble your own circuit for the wireless remote control. Solder wires from these tact switches to pads on the transmitter PCB corresponding the keys that the new tact switches need to proxy. Fit them all in a small door bell box, add batteries, close the box shut and you are done.

NOTE: Here is the list of various other Community Computers that I built using various other projectors and single board computers over the few months of my fellowship.

Thursday, November 12, 2015

Community Computer using Intel NUC PC

NOTE: Here is the list of various other Community Computers that I built using various other projectors and single board computers over the few months of my fellowship.

As I began my Teach For India fellowship, I got inspired by the K-Yan and decided to build my own community computer for my own class of 48 7th graders. I tried building one using a Raspberry Pi, but the results left much to be desired (Couldn't install Prezi, wasn't powerful enough, video player required commands to operate, no internal storage etc). That's when I came across Intel's Next Unit of Computing (NUC) PCs. These are small form factor PCs built for portable applications like interactive kiosks etc.

Since these PCs only have and HDMI output, I would need an HDMI capable projector. So I asked my friends for donations and went shopping and bought these:
  1. BenQ MS521p [Cheapest HDMI Projector]
    INR 30,000
  2. Intel DN2820FYKH [NUC PC]
    INR 9,340
  3. 8GB Low Voltage 1.35V SODIMM DDR3 RAM Kingston KVR16LS11/8 [For NUC PC]
    INR 3,300
  4. 2.5" SATA 500GB HDD Toshiba MQ01ABD050 [For NUC PC]
    INR 2,870
  5. HP S3000 USB Powered Speakers
    INR 729
  6. Logitech mk220 Wirless Keyboard/Mouse Combo
    INR 1,300
  7. HDMI Cable
    INR 790
So for under INR 48,500 I had managed to collect all the components:

I began by installing the HDD and RAM in the NUC PC and Installing Windows on it using a pen drive. Installing Google Drive on the PC (I have WiFi at school too), allowed me to sync stuff from my home PC to this Community Computer easily

Next I mounted all the components on a piece of plywood (I had to add in a powerstrip and phone charger to power the speakers) and voila!: I had an easy to carry community computer which took no time to setup and assemble at the start of the class because all the components were always wired together beforehand and did not need any connection and disconnection. The setup just had a single 3 core AC mains cable coming out of it. I could now go into my class, setup the projector, and show videos, photos, powerpoint slides, prezis and all kinds of content to my kids.

Carrying it around was still cumbersome and the plywood meant it wasn't sturdy enough.
Also, I had to carry the keyboard and mouse separately.

I was looking for a way to make it more compact and easy to carry.
That when Mr Rohit Garg, who owns a electronics goods and service shop here in Aundh, Pune suggested that I mount it in a casing meant for a voltage stabilizer. I gave him the current setup and this is what he came up with:

This made it immensely more sturdy. But the keyboard and mouse still had to be carried separately.
That and the ventilation was a big issue. I did not want the projector/PC's lives to be diminished just because of lack of ventilation. Rohit had made cut out for vents but somehow it did not seem enough for me. So I did away with the shell, and while I was at it, I added a lunch box to hold the projector's remote and wireless mouse. For the keyboard I added velcro (loop and hook) stickers to make it easy to stow inside the case itself. The Community Computer now had to be carried using two hands which was more comfortable. The keyboard, mouse and the projector remote are now stashed inside the community computer itself.

Community Computer frame with the keyboard and mouse stashed within it

Velcro hook stickers applied to the projector top to attach the keyboard

Velcro loops on back of wireless keyboard

Lunchbox lid attached to the community computer frame to hold the mouse and projector infrared remote
Front View

Intel has recently come up with the Intel Compute Stick. The compute stick is a cheaper replacement for the NUC PC. The stick has 32GB of eMMC storage (its like an SSD Hard Disk) and 2 GB of RAM already inside it. It retails for INR 9,800 on flipkart and comes pre-loaded with Windows 8.1:

NOTE: Here is the list of various other Community Computers that I built using various other projectors and single board computers over the few months of my fellowship.

Thursday, October 29, 2015

A Security Cam that pushes video clips to your phone: Motion Pie + PushBullet


Raspberry Pi running Motion Pie. USB Webcam is connected to it. A bash script pushes small snippets of videos (shot when motion is detected() to your phone.


  1. Signup for PushBullet and install the android app on your phone (and chrome extension on your browser)
  2. Take a Raspberry Pi and connect a Raspberry Pi Camera or USB Webcam to it. I used a UVC USB Webcam.
  3. Format a SD Card on your computer and write the Motion Pie image to it. Here is how to do it.
  4. Connect your Raspberry Pi to your home WiFi router using Ethernet cable. My house has CAT5 wire running through pipes concealed in the walls.
  5. Perform basic configuration on the Raspberry Pi using its web interface. 
    1. Administrator password. (Otherwise you wont be able to connect to it using SSH/PuTTY)
    2. Setting the timezone.
    3. Network setting - I used static IP address.
    4. Enable FTP write support.
    5. Video Device - Camera name or rotation etc.
    6. File storage: I used "network share" option to point back to the RPi's SD card folder shared over the network. Not sure why the default option of saving files to SD card did not work for me.
    7. Motion detection threshold - I set mine to 10% because I also have a motion activated light switch installed outside my door.
    8. Working Schedule - Make sure to cover all days and times of the week
  6. Use PuTTY to install a bash script ( on it.
    1. Make sure to set your PushBullet access token in the script.
    2. Before you can use nano to create a script file , you will need to remount the filesystem to make it writable. to do that issue the command: mount -o remount,rw /
      Read FAQ here.
    3. Mark the script as executable: chmod +x
  7. Configure the Raspberry Pi using its web interface to run the script when Motion is detected. This option is available under "Motion Notification"
  8. Put everything in an enclosure and install it near your door. In my case I used a lunch box to hold the RPi and its power supply (standard 5V USB smart phone charger). I installed the cam near the door and ran its USB came through my concealed wiring pipes embedded in the walls of my apartment.
  9. Wait for motion.


## Your PushBullet Access Token
## Fetch yours from your "Account Settings" Page:
## PushBullet API Documentation link:

## Following bash script function taken from
## It extracts value for a corresponding key from a JSON response.
function jsonval {
    temp=`echo $json | sed 's/\\\\\//\//g' | sed 's/[{}]//g' | awk -v k="text" '{n=split($0,a,","); for (i=1; i<=n; i++) print a[i]}' | sed 's/\"\:\"/\|/g' | sed 's/[\,]/ /g' | sed 's/\"//g' | grep -w $json_key`
    echo ${temp##*|}

## Get the current date and time
DATESTAMP=$(date +"%Y-%m-%d")
TIMESTAMP=$(date +"%H-%M-%S")

## Get the name of the latest AVI clip shot and placed with a folder on your Raspberry Pi's SD card
LATESTAVI=$(ls -tr1 /home/ftp/sdcard/$DATESTAMP/*.avi | tail -1 | sed 's#.*/##')

## The latest AVI might still be open and being written to.
## So if we try to upload the file rightaway, the file size will be reported to be greater than 25 MB
## and PushBullet will reject it. So we will wait for 30 seconds to allow the system to finish writing the file.
## Ideally we should use lsof utility to wait until the file is done writing, but lsof command is not available on Motion Pie.
sleep 30

## Pushing a file is a 3 step process
## Step 1: Send a request for file upload.
##    PushBullet will respond with a URL to which you can upload your file. (upload URL)
##    PushBullet will also respond with a URL at which the file will be available after upload. (File URL)
##   No push message is sent in this step.
##   File is not uploaded in this step.
##   Documentation:
## Step 2: Upload the file to the URL which was assigned to you in Step 1
##   Documentation:
## Step 3: A push need to be sent for that file. This push can include a message as well as the File URL generated in Step 1.
##   Documentation:

## Step 1: Request file upload
json="$(curl \
--header 'Access-Token: '$ACCESSTOKEN \
--header 'Content-Type: application/json' \
--data-binary '{"file_name":"'"$LATESTAVI"'","file_type":"video/avi"}' \
--request POST \"

## Extract the JSON fields: espesially the Upload URL and File URL




## Step 2: Upload the file
echo "About to  upload $LATESTAVI to $UPLOAD_URL"
curl -i -X POST $UPLOAD_URL -F file=@/home/ftp/sdcard/$DATESTAMP/$LATESTAVI
echo "Done uploading. File now available at $FILE_URL"

## Step 3: Send a push message including a link to the file. 
## If the Push is received on a smart phone, the file will be automatically downloaded to it.
echo "Now pushing the file $LATESTAVI to Devices."
curl \
--header 'Access-Token: '$ACCESSTOKEN \
--header 'Content-Type: application/json' \
--data-binary '{"type":"file","body":"Motion detected at '"$DATESTAMP $TIMESTAMP"'","file_name":"'"$FILE_NAME"'","file_type":"'"$FILE_TYPE"'","file_url":"'"$FILE_URL"'"}' \
--request POST \

My web configuration settings:

Make sure to set admin password. Set the timezone too.
Network settings may be needed if you don't want to use DHCP - it is always
better to ensure static IP address if you want to access
the live video feed using VLC app on your phone or a
computer from inside your own home network.

Enable FTP and Samba write support

Nothing much to change here.

Name the camera. Since I had mounted my camera upside down,
I had to set the rotation to 180 degrees.

Set the storage to Network Share and point it to the IP address of RPi itself.
Enter the appropriate credentials as well.

I set the motion detection threshold to 10% and
turned the frame changes ON (Pink square around the changing parts
of frame where motion is detected)

Working schedule set to cover all days and times.
The location of is mentioned here under Motion Notifications - make sure to perform that setting only after writing the script to the SD card using PuTTY.

Motion Clips and Screenshots

Motion detected notification on phone

Motion clip being played on phone

Motion clip being played on phone


Photos of hardware

All in a lunch box. Switch added to make the thing easy to turn on and off.

5V smart phone charger acting as Power Supply.

There is a security door in field of view of my camera, perhaps I should install
the camera outside this door to get a clear view of the person ringing the door bell

I use a webcam, it has infrared lights, haven't bothered to figure out how
to activate the illumination infrared LEDs over USB.....
...because I have a motion switch which turns on the porch light
whenever someone comes near the door.


  1. motionPie has been renamed to motionEyeOS and lives now at
  2. Get the latest SD Card image from:
  3. Installation instructions can be found here: