2 layers42 × 60 mm OndraMELODIK, the printed circuit board in 3D

OndraMELODIK

Music interface for the famous czechoslovak home computer Ondra SPO186

Size: 42 × 60 mm
Copper layers: 2
Thickness: 1.6 mm
Parts: 22
Nets: 41
Pads: 149
Tracks, vias: 438, 10
Routed: Yes
KiCad: KiCad 6 (file 20211014)
Created: 24 Aug 2022
Updated: 10 Feb 2026

Overview

OndraMELODIK is an open-source printed circuit board by 72ka, from the 72ka/OndraMELODIK repository on GitHub, published under the MIT licence. It is a 2-layer board of 42 × 60 mm with 22 parts on 41 nets, routed with 438 tracks and 10 vias.

It is built around the 74LS00SC and 74LS74PC. Its parts include 6 resistors, 5 switches, 4 capacitors, 3 ICs and 1 diode. It belongs with the interfaces and adapters boards of this library.

Main components

README

README.md

OndraMELODIK

Music interface for the famous czechoslovak home computer TESLA Ondra SPO186

SMD version with Joystick interface, but without printer connector by Solaris104 here: Ondra JOY/MELODIK.

You can read the OndraMELODIK story in this article (Czech language)

OndraMELODIK music interface - introduced in 2022

Czechoslovak home computer Tesla Ondra SPO186 - introduced in 1985

Features

Opensource hardware
Based on SN76489 chip
Compatible with OndraSD interface, OndraMELODIK is through out interface
It can play 3 channels square wave, 1 channel noise simultaneously
Minimum CPU usage - two byte transfer, in some cases even one byte transfer, this is essential for such a slow computer
External interface - no changes on the computer
Designed with 80´ technology - all parts was available in 1985
DB25 Centronics printer port (formerly known as LPT from PC) in one case
3D printed case STL files included

Usage

Turn off your belowed Ondra
Plug OndraMELODIK to Ondra X1 connector
Optionally plug the OndraSD or whatever interface to the OndraMELODIK

As music interface

Switch the switch to the MELODIK position
Plug the 3.5mm audio jack of your favorite audio system
Turn on Ondra
If you hear some noise or tone, just push once the RESET button
Load the software meltest.bin from this repository and test the device and listen the music

Notice: If you perform just Ondra reset and some tone or noise is coming out, just push the RESET button once

As printer interface

Switch the switch to the PRINTER position
Be sure you dont have plugged in the audio jack or the audio system is turned off
Plug your printer using standard PC printer cable
Turn on Ondra
Print using Ondra's monitor, BASIC or TEDIT (if you forget to unplug the audio jack and strange noises are coming out, it is normal)

Preview

How it sounds

https://www.youtube.com/watch?v=u5RyUs0VGdg

How it prints

https://www.youtube.com/watch?v=VYsxnQOKPeM

Real photos

License

MIT license

Category and platform

Interfaces and adapters

Project files

Show this board on your page

https://pcbkit.io/boards/72ka/OndraMELODIK

The board's own page, for a message or a post.

Source

Repository: 72ka/OndraMELODIK
Board file: KiCAD/OndraMelodik.kicad_pcb
Commit: 0ab56e1
Licence: MIT

Parts

Qty	Value	Footprint	References
2	100n	Capacitor_THT:C_Disc_D3.0mm_W1.6mm_P2.50mm	C1, C3
2	10k	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R4, R5
2	470R	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R1, R2
2	ONDRA_X1	TESLA:TX5112011	K1, K2
1	100uF/6,3V	Capacitor_THT:C_Radial_D6.3mm_H7.0mm_P2.50mm	C4
1	12k	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R3
1	2k	Resistor_THT:R_Axial_DIN0207_L6.3mm_D2.5mm_P7.62mm_Horizontal	R6
1	4,7uF/50V	Capacitor_THT:C_Radial_D5.0mm_H7.0mm_P2.00mm	C2
1	4MHz	Crystal:Crystal_HC49-4H_Vertical	Y1
1	74LS00	Package_DIP:DIP-14_W7.62mm	U2
1	74LS74	Package_DIP:DIP-14_W7.62mm	U3
1	AudioJack	Connector_Audio:Jack_3.5mm_Lumberg_1503_07_Horizontal	J1
1	KA206	Diode_THT:D_A-405_P7.62mm_Horizontal	D1
1	MELODIK / TISK	Button_Switch_THT:SW_CuK_JS202011CQN_DPDT_Straight	SW2
1	Printer (optional)	Connector_Dsub:DSUB-25_Female_EdgeMount_P2.77mm	K3
1	RESET	Button_Switch_THT:SW_PUSH_6mm	SW1
1	SN76489	Package_DIP:DIP-16_W7.62mm	U1

The 21 most common of 22 parts.

Similar boards

2 layers365.1 × 203.2 mm
DIAG
Nakazoto/CenturionComputer
This is just a simple backup of all the files related to the Centurion that I have stored on my HD. The Wiki itself has far more in-depth information about the Centurion and it's individual cards.
150 parts172
2 layers134.6 × 208.3 mm
Ts2
jefftranter/68000
Code related to the Motorola 68000 microprocessor.
110 parts133
2 layers407 × 184 mm
TRS-80-Model I G E1
RetroStack/TRS-80-Model-I-G-E1
Hardware Replica of the TRS-80 Model I Revision G
230 parts57MIT
4 layers337.6 × 105.7 mm
ISA CGA
hkzlab/CGA_Redux
The Color Graphics Adapter Redux board is a more or less faithful clone of the original IBM CGA, based on the original schematics
170 parts56
2 layers350 × 224.3 mm
Console
danwerner21/TI99_22
a 2022 replica of the classic TI/994a, using obtainable parts
251 parts50
4 layers243.8 × 170.2 mm
HEC1
Andy18650/HEC-Model-Z1
A Z80 computer with protected mode support
126 parts36GPL-3.0
4 layers276.9 × 172.7 mm
Simplevideo
gfoot/compvideo6502
Composite/component video output for homebrew 6502 computers
65 parts36Unlicense
2 layers333.2 × 205.9 mm
Dragon64
danwerner21/Dragon64
A clone board for the Dragon64 and Tandy Color Computer
232 parts34

Questions

How big is the OndraMELODIK PCB?

It measures 42 × 60 mm and has 2 copper layers, 1.6 mm thick.

What parts does the OndraMELODIK use?

22 parts, built around the 74LS00SC and 74LS74PC. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.

Where can I download the OndraMELODIK KiCad files?

From the 72ka/OndraMELODIK repository on GitHub, at the commit this page was made from: the board is KiCAD/OndraMelodik.kicad_pcb and its schematic KiCAD/OndraMelodik.kicad_sch. PCBKit opens the board in the browser, with nothing to install.

Can I use the OndraMELODIK design in my own project?

Its repository publishes it under the MIT licence: you may reuse it on that licence's terms (keep the author's notice, and for a copyleft licence share your changes alike).