"A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects." (Robert A. Heinlein)

Saturday, 21 April 2018

Remotely controlling the Raspberry Pi Zero and Pi Camera


Here I am continuing my very slow paced building of a Raspberry Pi Zero based camera. After experimenting with raspberry-desktop file exchanging I’ve now took some time experimenting with remote controlling options. I’ll eventually have to wire to the Raspberry some, at least minimal, physical interface, but remote control, trough a Android smart-phone, could be a viable solution to avoid a too complex hardware interface.

The ready-made solution: Raspicam Remote

The first solution I found in Android Play store has been Raspicam Remote. Raspicam is a quite simple application providing a simple but complete user interface and connecting to the Raspberry Pi using Wi-Fi and SSH.
Unfortunately Raspicam doesn’t work on my old phone (Jelly bean) but it works fine in my much newer tablet. I understand you can’t keep backwards compatibility with everything. Other solutions are available but they look more suited for remote surveillance than camera interface.

The mostly Do-it-yourself solution: BlueDot

Interfacing to the Raspberry trough Wi-Fi offers clear advantages a specially in terms of connection speed but also poses some disadvantage. Setting-up a Wi-Fi connection might be trivial while at home where is available an already configured access point but it’s not the same while outside. Connecting the Raspberry with a smart-phone using Wi-Fi means configuring one of them to act as access-point, its not difficult but it might become tricky. Also on the power consumption aspect must be kept in consideration especially for the device acting as access-point.
Bluetooth overcomes both set-up and power consumption problems in exchange, of course, for transfer speed and connection range.
Here comes to play BlueDot: a simple looking Android application that together with a easy to use Python library allows a unidirectional Bluetooth communication between smart-phone and a Raspberry device.
Installing BlueDot means, on the Android side, just installing the BlueDot application from Android Play Store. On the Raspberry side some Python library is necessary. Since I’m quite new to Python and have no backward compatibility problems I’ve choose to use exclusively Python 3.
sudo apt-get install python3-picamerasudo apt-get install python3-dbussudo apt-get install python3-pipsudo pip3 install bluedot
Once everything has been installed the Raspberry and the phone must be paired in order to communicate freely over Bluetooth. I followed this tutorial and used the bluetoothctl command.
sudo bluetoothctl
this command has its own command line interface: the commands ...
agent ondefault-agent
enable the pairing agent, then the command …
scan on
start scanning for available devices. Once the my phone has been listed …
pair <device-id>
start the pairing procedure.
When all preliminary operations have been completed I verified BlueDot was working by starting the simple demo Python scripts available at BlueDot site. Among the already povided BlueDot demos one is dedicated to taking a photo at the press of application “blue dot”.

Sending back photos using Bluetooth

BlueDot is a one-way-only communication system, so I thought on I the raspberry could send back photos to cell-phone. The file transfer protocol over Bluetooth most commonly used is called OBEX FTP, back some year ago, when most phones didn't have wireless support, it was more common having to deal with it. Now it’s almost forgotten but still supported both from Linux and Android phones.
OBEX FTP is installed on Raspbian with the following command
sudo apt-get install obexftp bluetooth
As install completed I’ve been able to interrogate my, already paired, phone for available Bluetooth services.
sudo sdptool browse <device-id>
Among the available services I took note of the channel number (12 in my case) of “OBEX push service” the one allows receiving files like a message. After some searching on the Internet I eventually came to the right command to send a file:
obexftp --nopath --noconn --uuid none –bluetooth <device-id> --channel <channel> -p <file>
File transfer is quite slow, even slower than I used to remember, so is not fit as main file transfer mean but it could be enough to get a preview from a display-less camera.