Optical string-tuning tool

This tool assists you in tuning your string instrument to a given tone. It utilizes the stroboscopic effect to give feedback about the adjustment of your instrument. The two LEDs on the board blink with the frequency that the chosen tone has. When the string vibrates with the correct frequency, two lines are projected at a fixed position on the string. If frequencies don't match, the lines appear to be blinking or moving to the observer's eye. The moving or blinking effect decreases with decreasing difference between the two frequencies.

Menu

The "Stimmmopped" has two switches to choose the tone and instrument. Switch S1 toggles the current mode of the menu, which is either "choose instrument" or "choose tone". The 7-segment display displays the current selection. In the instrument selection mode, the display is lit up a bit brighter. Switch number two (S2) selects the tone or instrument in the given mode.

Here's how the menu is structured:

Displayed character	Name	Explanation
b	Bass (5-string or dropped)	b0 (string 5), d1 (string 4 dropped), E1 (string 4), A1 (string 3), d2 (string 2), G2 (string 1)
b.	Bass (5 string) lower halftone	A#0 (string 5), C#1 (string 4 dropped), d#1 (string 4), G#1 (string 3), C#2 (string 2), F#2 (string 1)
G	Guitar (normal & dropped)	d2 (string 6 dropped), E2 (string 6), A2 (string 5), d3 (string 4), G3 (string 3), b3 (string 2), E4 (string 1)
G.	Guitar (normal & dropped) lower halftone	C#2 (string 6 dropped), d#2 (string 6), G#2 (string 5), C#3 (string 4), F#3 (string 3), A#3 (string 2), d#4 (string 1)

When the menu is in tone setting mode, the tone and octave are displayed alternating.

Since the device is battery powered, it switches itself off when no button is pressed for a period of 30 seconds. It may also be manually switched on and off by holding down the S2 switch. In normal usage conditions the battery will last for about a year.

Circuit board

The board is designed to be used as a plectrum. Here's the layout:
 

Click to enlarge

Part list

Amount	Part	Description
1	ATmega48-20AU	Microcontroller
1	8,0000-HC49U-S	8MHz Quartz
3	CR 2032	Battery (a set of 3)
1	KZH 20-1	Battery holding unit
2	NPO-G0805 22P	Capacitor for the Quartz
2	SMD-0805 47,0Ω	Resistors for the LEDs
8	SMD-0805 560Ω	Resistors for the 7-Segment
2	LED 5-4500 RT	LEDs for the strings
2	X7R-G0805 100N	Capacitor
2	TASTER 3301	Switch
1	SMD TAN.22/20	Capacitor
1	SA 39-11 GN	7 segment display

Source

Sourcecode & Layout can be found in our svn right here.

Links

Information about midi notes 

das-labor.org