akreager/cd_changer_emulator8Raspberry Pi CD changer emulator for 1990s Kenwood car stereos. Reverse-engineers the 13-pin DIN serial protocol and replaces the changer with a Pi HAT featuring ATtiny1616, PCM5102A DAC, and automotive power management.
Changer cable breakout is an open-source printed circuit board by akreager, from the akreager/cd_changer_emulator repository on GitHub, published under the MIT licence. It is a 2-layer board of 22 × 80 mm with 5 parts on 16 nets, routed with 140 tracks and 0 vias.
It is built around the SDD-130J. It belongs with the audio and music and interfaces and adapters boards and the AVR (ATmega, ATtiny) boards of this library.
This KiCad project implements a passive, pass-through breakout board for the Kenwood KRC-3006 head unit's 13-pin mini DIN connector. The board provides:
COMPLETE AND TESTED — Boards received 2026-03-28 from OSH Park. S/N 1 verification completed 2026-04-10, per TL-02-01-20260410. Its step 1.1 result remains a closeout question (DC-13). Breakout board is fully functional and ready for protocol reverse engineering work.
| Ref Des | Component | Function |
|---|---|---|
| J1 | SDD-130J, 13-pin mini DIN female | Head unit side connector (front side) |
| J2 | SDD-130J, 13-pin mini DIN female | Changer side connector (back side) |
| J3 | 1×11 female pin header, 2.54 mm pitch | Digital/control signal test points |
| J4 | STX-3100-3NB, 3.5 mm TRS audio jack | Head unit side audio breakout |
| J5 | STX-3100-3NB, 3.5 mm TRS audio jack | Changer side audio breakout |
| Pin | Signal | Description |
|---|---|---|
| 1 | REQ H (Active Low) | Request handshake output from head unit. |
| 2 | GND | Ground (factory name; DN-02 §1). |
| 3 | B.U. | Battery Unswitched. |
| 4 | ON | Changer connect/enable signal. |
| 5 | MUTE | Mute request line. |
| 6 | D. GND | Digital ground. |
| 7 | RESET | Reset pulse output to changer. |
| 8 | R CH | Right audio channel, analog. |
| 9 | REQ C (Active Low) | Request handshake output from changer to head unit. |
| 10 | DATA C | Serial data from changer to head unit. |
| 11 | DATA H | Serial data from head unit to changer. |
| 12 | L CH | Left audio channel, analog. |
| 13 | CLK (Active Low) | Synchronous clock. |
| J3 Pin | J1 Pin | Signal |
|---|---|---|
| 1 | 2 | GND |
| 2 | 4 | ON (CH-CON) |
| 3 | 3 | B.U. (+14V) |
| 4 | 7 | RESET |
| 5 | 6 | D. GND |
| 6 | 1 | REQ H (Active Low) |
| 7 | 9 | REQ C (Active Low) |
| 8 | 5 | MUTE |
| 9 | 10 | DATA C |
| 10 | 11 | DATA H |
| 11 | 13 | CLK (Active Low) |
| J4 contact | J1 pin | Signal |
|---|---|---|
| Tip | 8 | R ch (to head unit) |
| Ring | 12 | L ch (to head unit) |
| Sleeve | 2 | GND |
| J5 contact | J2 pin | Signal |
|---|---|---|
| Tip | 8 | R ch (from changer) |
| Ring | 12 | L ch (from changer) |
| Sleeve | 2 | GND |
These are contact labels, not numbered pins. Mapping follows approved R-4, which cites the PCB and TL-02 steps 1.12–1.13 and 3.3–3.4. This corrects the README labels only.
The audio channels (Pin 8 - R CH and Pin 12 L CH) are not routed as a direct pass-through between J1 and J2. Instead, they are broken out to two 3.5 mm TRS audio jacks mounted on the right edge of the board:
The audio jacks use a standard 3-conductor (TRS) footprint with no switching contacts. When nothing is plugged in, the audio pins on both the head unit and changer sides float.
This topology enables three operating modes:
| Mode | Configuration | Use Case |
|---|---|---|
| Audio pass-through | Connect J4 to J5 with a male-to-male 3.5 mm TRS cable. | Normal protocol capture with authentic changer audio reaching the head unit. |
| Audio intercept | Connect monitoring equipment (oscilloscope, audio recorder, powered speakers) to J5. | Listen to or record the changer's audio output without routing it to the head unit. |
| Audio injection | Connect an external audio source to J4. Leave J5 disconnected or connected to monitoring equipment. | Feed test tones or music from a phone, DAC, or Raspberry Pi directly into the head unit's audio input path. Useful for verifying the audio path independently of changer protocol state. |
Audio pass-through requires the external cable. The board cannot function as a fully transparent sniffer without it. This is an intentional design decision — the separate jacks provide flexibility that a hardwired pass-through cannot.
S/N 1 supported TP-01 Phase 1 on 2026-04-19. Next, follow TP-01 Rev C:
For every analyzer connection follow DN-04 §7: power down, block J3-3, ground only at J3-1, leave J3-5 empty, use the custom crimped harness and cover exposed rear joints (R-2).
| Rev | Date | Author | Changes |
|---|---|---|---|
| — | 2026-10-17 | A. Kreager | R-4: correct J4/J5 contact and channel labels. DC-05/13: factory ground name, recorded completion date and TP-01 Rev C work order; link FIX-01 instructions. |
| Qty | Value | Footprint | References |
|---|---|---|---|
| 2 | AudioJack3 | Library:Jack_3.5mm_CUI_SJ1-3523N_Horizontal | J4, J5 |
| 2 | SDD-130J | Library:CUI_SDD-130J | J1, J2 |
| 1 | Test Points | Library:PinSocket_1x11_P2.54mm_Vertical | J3 |
akreager/cd_changer_emulator
Raspberry Pi CD changer emulator for 1990s Kenwood car stereos. Reverse-engineers the 13-pin DIN serial protocol and replaces the changer with a Pi HAT featuring ATtiny1616, PCM5102A DAC, and automotive power management.
joypad-ai/joypad-os
Universal controller firmware for building adapters, dongles, and custom controllers.
OLIMEX/OLINUXINO
OLINUXINO is Open Source / Open Hardware, low cost from EUR 24 Linux Industrial grade Single Board Computer capable to operate -25+85C
jamro/tiny-engineer
A small desktop robot that brings an AI coding assistant to life, physically acting out when it reads files, thinks, writes code, and finishes work.
hackclub/OnBoard
💡 Join 1,000 teenagers and make your first PCB with a $100 grant!
Luos-io/luos_engine
Open-source and real-time orchestrator for cyber-physical-systems, to easily design, test and deploy embedded applications and digital twins.
It measures 22 × 80 mm and has 2 copper layers, 1.6 mm thick.
5 parts, built around the SDD-130J. 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.
From the akreager/cd_changer_emulator repository on GitHub, at the commit this page was made from: the board is hardware/kicad/changer cable breakout/changer cable breakout.kicad_pcb and its schematic hardware/kicad/changer cable breakout/changer cable breakout.kicad_sch. PCBKit opens the board in the browser, with nothing to install.
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).
