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'Sound Kit' electronics kit

'Sound Kit' is an electronics kit aimed at young people. Correctly soldering the components onto the included printed circuit board (PCB) creates a badge that visualizes the volume and frequency (the pitch) of sound via the microphone. As a bonus, the badge also creates a light scanner like used for example used by Kitt in the Knight Rider series.

English text Er is ook een pagina in het Nederlands aanwezig.

Sound Kit front back

The front and back of a ready built Sound Kit.


You can send your questions about the Sound Kit project to ivo [atsign] digiterraan.nl.

The engineers

Ronald PA5RB, Ivo PA1IVO and Leo PA0LEZ.

Thanks to

Building instructions

The building instructions can be found in a colour PDF file. When printing the manual, use a colour printer in order to see the red lines in the pictures. The instructions are only available in Dutch, but the instructions will be useful for everyone due to the graphical presentation.


In the manual you can find all the information you need to know to operate the Sound Kit, however in Dutch only. It is a PDF file in A4-format, containing two A5 columns of text. By double-side printing the A4 and cutting it exactly into two equal parts, you get two manuals in A5 format.

Spectrum mode testing

By playing the special .wav file, the spectrum mode of your Sound Kit can be tested. Hold your Sound Kit close to the speaker: the .wav file plays first eight tones that will light the leds one-by-one and second four dual tones that light two leds simultaneously.

The .wavfile plays the following tones:

500 - 750 - 1000 - 1250 - 1500 - 1750 - 2000 - 2250 - 500+1500 - 750+1750 - 1000+2000 - 1250+2250 Hz.


Schematic Sound Kit
Schematic of the Sound Kit electrical circuit.

Electronic parts

Part & reference Name / value Manufacturer part number Supplier & order code
Resistors R1,R4,R17 2.7 kΩ 1% VISHAY MRS25000C2701FCT00 Farnell 9466827
Resistors R2,R3,R5 33 kΩ 1% VISHAY MRS25000C3302FCT00 Farnell 9467351
Resistors R6,R7 15 kΩ 1% VISHAY MRS25000C1502FCT00 Farnell 9464689
Resistors R8 ... R16 1 kΩ 1% VISHAY MRS25000C1001FCT00 Farnell 9465170
Capacitor C1 1.5 nF (pitch 2.54 mm) KEMET C320C152J1G5TA Mouser 80-C320C152J1G
Capacitors C2,C4,C5 4.7 µF (6.3 x 11 mm) RS Pro 711-1784 RS 711-1784
Capacitors C3,C6,C7,C8 10 nF (pitch 5.08 mm) AVX SR211C103KAR Farnell 1100407
Leds D1 ... D8 5 mm red 120° - LEDs-buy 08-05-02-RO
Switches SW1 ... SW4 Tactile Switch off-(on) ALPS SKHHARA010 Mouser 688-SKHHAR
Microphone MK1
Reichelt MCE 100
(Farnell 2396073)
IC socket U1 28 pins (2 x 14) 7.62mm spacing ASSMANN WSW AR 28 HZL/7-TT RS 674-2498
IC socket U2 8 pins (2 x 4) 7.62mm spacing ASSMANN WSW AR 08 HZL-TT RS 674-2479
Microcontroller U1 ATmega88V-10PU Atmel ATmega88V-10PU Mouser 556-ATMEGA88V10PU
Op Amp U2 Low-Power Op Amp Microchip MCP6002-I/P Farnell 1292245
BT1 Battery holder 2 x AAA Keystone Electronics 2468 Mouser 534-2468
Batteries 2 x 1,5 Volt AAA - -

Sound Kit parts
Electronic parts Sound Kit.

PCB layout

The PCB layout is available as: The PCBs are manufactured at Safe-PCB.


The microcontroller (ATmega88, device signature 0x1E930A) firmware is available as .hex file. The fuse bits settings are: 0xF9, 0xD6, 0xE2 (extended, high, low).

Auto calibration

The microcontroller uses the internal RC oscillator as clock base, which is factory calibrated. To check and possibly improve the factory calibration, the auto calibration function is available in the Sound Kit. For determining the sound frequencies in the 'Spectrum mode' it is important that the clock runs at the correct frequency of 8 MHz (the clock is not divided by 8 by means of the CKDIV8 fuse).

For pre packed kits the auto calibration has already been done, so it only needs to be performed when you are programming the microcontroller yourself.

The auto calibration uses an external signal as an reference:

Auto calibration procedure:
  1. Remove the power from the PCB.
  2. Connect the external 1 kHz signal between pin 9 (PB6) and ground at pin 8 (GND).
  3. Connect pin 10 (PB7) to ground somewhere (for example pin 8 or pin 22 or another ground on the PCB).
  4. Supply the power (3 V) to the PCB again.
  5. The Sound Kit will now perform the auto calibration for about 15 seconds. The calibration found will be stored in EEPROM so it will also be available after a power loss.
  6. When the auto calibration is ready, the "disco mode" will start automatically.
  7. Remove the external signal from pin 9 and the connection on pin 10.
Pin 14 (PB0 / TP1) outputs a square wave signal which (at an exact internal clock frequency of 8 MHz) toggles every 64 µs, and thus provides a 7.8125 kHz square wave. By monitoring this point the calibration can be checked. During the auto calibration you can monitoring the 'search algorithm' for the correct calibration value.

2018-2023 by Ivo Klinkert, PA1IVO - Contact