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There's also a similar, commercial device available:
There's also a similar, commercial device available:
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Aktuelle Version vom 3. Januar 2012, 09:53 Uhr


Release status: stable [box doku]

Description The "Stimmmopped" is a tool to tune musical string instruments (i.e. guitars)
Author(s)  Madex (Martin)
Last Version  0.21
Platform  AVR (ATmega48 oder ATmega88)
License  GPLV3
Download  SVN browse

Optical string-tuning tool[Bearbeiten]

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.


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[Bearbeiten]

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




Part list[Bearbeiten]


Amount	 Part		  Description	                Price
1	 ATMEGA 48-20 AU  Microcontroller	        € 1,25
1	 8,0000-HC49U-S   8MHz Quartz	                € 0,18
3	 CR 2032	  Battery (a set of 3)		€ 0,35
1	 KZH 20-1	  Battery holding unit	        € 0,45
2	 NPO-G0805 22P	  Capacitor for the Quartz      € 0,05
2	 SMD-0805 47,0Ω	  Resistors for the LEDs        € 0,10
8	 SMD-0805 560Ω	  Resistors for the 7-Segment	€ 0,10
2	 LED 5-4500 RT	  LEDs for the strings          € 0,25
2	 X7R-G0805 100N	  Capacitor 	                € 0,05
2	 TASTER 3301	  Switch	                € 0,10
1	 SMD TAN.22/20 	  Capacitor	                € 0,17
1	 SA 39-11 GN	  7 segment display           	€ 0,43

The total sum amounts to € 5,43 (without the circuit board).


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


Information about midi notes

There's also a similar, commercial device available: [1]