AVBus Protocol

This Project aims to reverse engineer the AVBus protocol of the Marantz ST560 Stereo Tuner.

Using the AVBus protocol it is also possible to control multiple HiFi devices from that device line, for example the PM451 Amplifier.

The main purpose of this repo is to serve as documentation. The code in here were my first attempts and I'll consider removing them.

Instead there's an implementation of the protocol for ESPHome. For details have a look at the ESPHome Section, or check out the sources in the AVBus Fork of ESPHome.

Devices

RMC-20AV

ST560

AV-Bus Jacks

PM-451

Ports

• There seems to be no difference between the IN and OUT jack
• It seems like most of the frames are sent on the Remote Control Bus (the orange one). I currently have no clue what the EasyBus (green) is for.
• Voltage on the bus is 5V
• The default state of the Bus signal is HIGH.

Protocol

The following section describes the protocol.

DISCLAIMER: The captures shown in the screenshots were captured with sigrok/PulseView

Frame

NOTE: Not the full Footer is shown here as it is much to long.

Each frame has the following structure:

Header	Data	Footer
10ms	8 Bits a 1ms	282 ms

This sums up to 300ms for each transmitted signal. The Header and Footer pull the bus to LOW.

Bits

A bit is 1ms long. The bus is pulled to HIGH to start a bit and then pulled to LOW. For a 1 the the HIGH phase lasts for 300us for a 0 for 700us. The remaining time the bus is at LOW.

1	0
300us HIGH	700us HIGH

Data

The data section of each frame consists of 8 bits. It seems like the first 3 Bits define the device and the remaining ones the command.

WARNING:

The commands never overlap so maybe it's just a coincidence that the devices start with the same 3 bits. On top of that, some commands for TV that should be sent aren't. Some investigation is needed whether they may be sent on the EasyBus.

Let's take the following capture of the Amp | Volume Down command as an example:

The first three bits are 0b101 or 5 which corresponds to Amp.

The last five bits are the command, which are 0b11101 or 0xD which in turn means Volume Down when combined with Amp.

Repeat

To repeat a signal the Footer is just extended by keeping the bus at LOW for the time the key is held on the remote. Exact timings need to be checked.

Codes

Device	Address	Function	Command
Amp	5	Vol+ (Front)	0x1E
		Vol- (Front)	0x1D
		Vol+ (Rear)	0x02
		Vol- (Rear)	0x12
		Mute	0x13
		Tuner	0x0A
		Phono	0x08
		CD	0x11
		Tape	0x18
		TV	0x09
		Video	0x07
		VCR	0x06
Tuner	6	AM	0x05
		FM	0x04
		Tune Down	0x00
		Tune Up	0x01
		1	0x0E
		2	0x0D
		3	0x0C
		4	0x0B
		5	0x0A
		6	0x09
		7	0x08
		8	0x07
Tape	3	Play	0x1E
		Stop	0x1B
		Rewind	0x1D
		Forward	0x1C
		Pause	0x1A
		Record	0x12
		Record Mute	0x18
		Direction	0x15
		Index Scan	0x19
		QMS	0x14
		Memo	0x17
Phono	6	Play	0x1E
		Cut	0x1B
		Cue	0x1A
		Repeat	0x16
VCR	2	Selector	0x15
		Memo	0x17
		Record Mute	0x18
TV	7	Play/Next	0x1E
		Stop/C	0x1B
		Pause	0x1A
		Repeat	0x16
System	1	1	0x1B
		2	0x1A

ESP Home Integration

I found it very convenient to integrate this protocol into ESPHome. With a little bit of circuitry, an ESP and some spare time, you will quickly be up an running.

If you haven't done so, start with setting ESPHome by following their guide.

To use the AVBus Protocol you can find a ready made custom component here.

Configuration

To use the custom component, include it in you ESPHome device config:

external_components:
  # use remote_receiver/remote_transmitter with AvBus support
  - source:
      type: git
      url: https://github.com/jodoll/esphome
      ref: avbus_protocol
    components: [ remote_receiver, remote_base, remote_transmitter ]

Then follow the instructions for remote transmitter/receiver in the official documentation.

Receiver

When including the external component, there's the avbus protocol available. Make sure you set idle to at least 11ms, as the Header of the protocol is 10ms long. When using a value that is too big, the receiver might not be able to decode values in fast sequence (it needs to wait until the signal is completed (idle) before moving on with the next one). I found that 20ms works quite well.

remote_receiver:
  dump: avbus
  pin: D2
  idle: 20ms

Transmitter

There's nothing special about the transmitter, just make sure to set carrier_duty_percent to 100%.

remote_transmitter:
  pin: D3
  carrier_duty_percent: 100%

Devices & Co.

Defining switches, automations, etc. is similar to other protocols, just us avbus as name.

# Individual switches
switch:
  - platform: template
    name: "AvBus Amp Vol Up"
    turn_on_action:
      remote_transmitter.transmit_avbus:
        address: 5
        command: 0x1E

Circuit

Here's how I've done the wiring for my ESPHome. It' might not be perfect, but it seems to work.

Note that the inversion of the signal for the receiver is (probably) not needed, as ESPHome will detect what's idle and will adjust accordingly.
On the transmitting side, however, signal inversion is a must.

CAUTION: The bus works at 5V while ESPs work at 3,3V. Don't just connect the bus to a pin without a transistor. You'll damage your ESP!

Used Parts

Name	Description	Amount
Q1, Q2	BC547B	2
R1	Resistor 1 kOhm	1
R2, R3	Resistor 10 kOhm	2
R4	Resistor 1500 Ohm	1
AvBus Output	RCA Jack	1

Third Party Software

• ArduinoJson (MIT)
• Arduino Core Avr
• Arduino Core Esp32 (LGPL v2.1)
• DS3231 (GPL v3)
• ESP Async WebServer (LGPL v3)
• FS (LGPL v2.1)
• PathVariableHandlers (MIT)
• RichHttpServer (MIT)
• Update (LGPL v2.1)
• WebServer (LGPL v2.1)
• WiFi (LGPL v2.1
• Wire (LGPL v2.1)

Todo

Electrical

• It seems the ST560 somehow get's stuck and doesn't accept any singnals from an actual remote control anymore when the ESP restarts while connected

Protocol

• Record and protocol all signals
• Narrow down timings for HEADER, 0, 1 and FOOTER
• What's the threshold where FOOTER makes a device repeat the command

Documentation

• Add diagram of wiring
• Add diagram of the bus signals