Thursday, 15 October 2015

Guitar tutor - 12 frets done

A little while back, we started a project that has been a bit of a brain-itch for a while: a light-up-LED-neck guitar tutor. We got our idea working for the first 12 frets on the guitar neck and - as every good guitarist will tell you - everything on the guitar repeats from the 12th fret onwards. So every time we light up the first fret, for example, we should light up the 13th. If the 5th fret is lit, the (12+5=) 17th fret is also lit up.

This basically means that once we've got the first 12 frets working, we need to simply recreate the original design, with less space between the LEDs (since the frets get closer together the further up the neck you go).

With this in mind, we're concentrating on getting the firmware working for the first 12 frets on our guitar tutor. As it turns out, each "string" of 12 LEDs is actually made up of three sections of four LEDs in a row. So it's not really much more than a bit of bit-shifting that gets our patterns out onto the guitar neck. But because the entire fingerboard is made up from a number of sections, we had to play about with bit-shifting to get the right pattern to appear in the right section. In particular, we had to make sure everything worked properly, even when it spanned two (or more) PCB sections.

Here we're making sure that good old pentatonic box one works correctly, even when split up over two different sections of PCBs. Eagle-eyed readers will spot that it's actually the "blues" version of the pentatonic box one, with the added flatted fifth - the "blues note".

Here's a video showing how the firmware can display chords, scales and patterns, for the first 1-12 frets along the neck.

In a final version, the nasty orange wires placed over the top of the PCBs would obviously be tracks running on the reverse of a double-sided board. But for home-etching, and to simply prove the concept works, big, ugly, surface-laid wires will suffice!

For those interested, the patterns displayed are all in the key of A:

  • pentatonic box one
  • pentatonic box two 
  • pentatonic box three
  • pentatonic box four (note how the pattern "wraps around" - what appears on frets 1-4 would also appear on frets 13-16 if there were in place on the neck)
  • pentatonic box five
  • A major chord (E-shape)
  • A minor chord (E-shape)
  • A major chord (A-shape)
  • A minor chord (A-shape)
  • A major chord (C-shape barre)
  • A major chord (D-shape barre)
  • "BB King Box"
  • "Albert King Box"
  • "Clapton Box"
  • Entire pentatonic scale - all positions

The patterns then repeat, this time with the root notes (A) highlighted by flashing them at 250ms intervals. The ability to highlight "target notes" can be very useful when learning to play melodic phrases, so we might even look at highlighting other notes in the scales, such as the thirds, flatted thirds and fifths, to help us mix the major and minor sounding scales.