Christmas lights : lightshowpi

 I have a very simple some coloured  5050 LED strips which provide a very colourful addition to Christmas.  Lightshowpi (LSPi) is wonderful Raspberry Pi (RPi) software which analyses music and allows you to configure lights accordingly.  I think most people use it with relays and big external displays but I prefer a small indoor spectacle when listening to Christmas songs.  My LSPi setup tends to change each year and this years effort works well.

The Raspberry Pi has rubbish sound quality through the headphone jack.  This year I attached a USB audio card which only cost about £5 and provides a signal quality which I can send through my hi-fi (is it still called that) to play pleasant sounding music.  It is possible to spend a more money (£60-£130) on an RPi DAC HAT or high quality USB audio but this is quite acceptable to me.

All my music is accessible using the venerable linux music player daemon (MPD) on an RPi which has a share to network attached storage (NAS) and can stream radio stations.  I use a web interface to mpd  so I can select, play and manage music from a browser.  LSPi is quite happy playing an http or icecast stream from MPD and I can direct its output to the USB audio card.

Previously I used bluetooth connection from RPi/MPD to my hifi but this makes synchronisation a little tricky as bluetooth introduces a selay of 2-3 seconds.  When playing sound through the USB card LSPi synchronisation is much better and I can see the colours changing in time with the notes.

The 4 colour LED strip runs at 12V and requires three GPIO pin signals to control Red, Green and Blue output.  The RPi can only provide 5V, limited current output so I have a simple setup with MOSFETs driving the LED strip with an external power supply.

Bash in full screen mode with colour

 I rarely use a linux GUI and I find that command line output is often dull and difficult to read.  It is easy and common to embellish the shell prompt with extra information and colours.  Also it is possible to amend colours for directory listings, editor entities etc. and I found a good list of ideas on stackexchange.  I would like to be able to do some simple formatting tasks on displayed screen output, such as putting text at a specific cursor position, in colour, perhaps surrounded by a box as shown below.

I can do this with a few escape codes in a script as shown below.

We start with a command to clear the screen \e[2J.  The \e causes the escape character to be sent, and the following three characters are a "vt100 escape code".  A VT100 (see below) was a screen introduced by Digital Equipment Corporation in 1978, one of the first to support escape codes.  I used vt100s in the early 1980s for programming and became very familiar with their capabilities.  DEC produced wonderful minicomputers in the 1970s and early 1980s but fell from grace and were consumed by Compaq, who in turn were digested into HP.  When working for HP in the 2010s I talked to a few of the engineers who had remained after the demise about the good old days and we lamented the passing of a great company.

Returning to the subject we can see the command to clear a screen in a list of VT100 escape codes which includes "esc[2J" to clear the screen and "esc[<v>;<h>H" to position the cursor. Thus "esc[6;20H" positions the cursor at row 6, column 20.  Note that the linux TERM variable does not need to be set to vt100 for this to work, it worked for me with TERM=xterm or TERM=xterm-256color.

For line drawing characters we use VT100 character codes. In the table we see that unicode characters 

\u2500, \u2502, \u250c,\u2510,\u2514,\u2518 are what we need to draw the box.  We need quite a few \u2500 characters to draw the horizontal box line.  What we have so far gives us a very presentable box around our title.

We now want to add a bit of colour to the text / box, which is easy.  I googled a simple reference at bluesock. Within a bash script it isa easier to use variables for colours and unicode characters and I changed my script so that it was a bit more understandable when colouring it in.  For example to set text to cyan I used the variable $COLOR_LIGHT_CYAN with value "\e[1;36m"

We now have the capability to control our ssh shell display layout.  Clearly it would be a real pain to format our screens like this in practice but I find it really useful to be able to understand how to do it at this level.  One could setup a standard bash script containing variables for all the options/colours you use or combine with other linux utilities, for example tput for clearing the screen and positioning the cursor.

I like the idea of a simple C program to do some of the work.  I find bash a bit painful for processing and it makes sense to use C for this.  As an exercise I redid the title box in C without any extra thought.

It is very simple, you just invoke gcc to compile it, and I saved it as /usr/local/bin/colourtitle.  I could then display the title putting colourtitle in a script.  Of course I need to accept a title as an argument and allow selection of colours but this provides an easy proof of concept.