Controlling Marantz amplifier using Arduino via “Remote” socket

Recently I decided to control my old Marantz PM-62 programmatically. There were a few reasons to do so:

1. Original remote control died and "compatible replacements" were not good enough.
2. I want to build more complex integration and routing for audio/video, so amplifier input switching would be a part of it.
3. It is fun

Playing with "Remote" socket

I found that there are 2 standard RCA sockets named "Remote IN/OUT" on the back panel. So I connected with the oscilloscope to the OUT plug and tried to use different buttons on the remote control. Soon I understood that this output shows signals received from the IR sensor, after amplifier (impulses are about 6V) and without carrier frequency. An interesting fact is that it sends here all commands, including one unit cant understand. Also, I found that there are 2 very different types of codes, with different lengths and impulse counts. I was also able to use a cheap Saleae clone (8ch, 24MHz) with a PulseView instead of the oscilloscope.

Native format and scan codes

I identified that Marantz using 2 different ways to encode the signal.

• Standard RC-5 encoding with 14 bits of data. Pulseview can decode such data using the IR RC-5 decoder. It has 2 fields – address to choose the device and command to send.
• Marantz RC-5 extension – this adds one more field, called extension. Also, this format adds pause after the first 8 bits, likely to simplify the identification of it. This format is not supported by PulseView protocol decoders.
• Both formats require at least 2 packets sent with Toggle bit flipped. I spent a lot of time trying to understand why it is not working for me until found that.

After all, I have been able to identify all scan codes from the original RC:

Name Address Command Extension Standby 16 12

Phono 21 63

CD 20 63

Tuner 17 63

AUX 1 16 00 06 AUX 2 16 00 07 DCC ON/OFF 23 63

TAPE ON/OFF 18 63

Volume + 16 16

Volume – 16 17

Finally making hardware to control it

I had a few Arduino mini clones, so decided to start with it. Initially, I started with Arduino IRremote library but soon found that impulses it generating are not something I am looking for:

• By default, it is re-creating carrier PWM impulses needed for real (wireless) IR transmit. This could be disabled by the USE_NO_SEND_PWM definition, but that causing an inverted signal with active HIGH. The amplifier was not able to recognize such a signal.
• There is no code for 20bit RC-5 anyway

So I decided to quickly write my replacement, without using this library. It is done and published on my gist. This code does not require any external libraries and can send RC5 and RC5-20bit to the amplifier in the way it understands it. Some code is taken from Arduino-IRremote. I also did a patch to PulseView decoder to understand Marantz’s format, which I will PR to the upstream later.

To control the device you need to connect the RCA jack to GND and D5 pins. Once the program is loaded it will switch amplifier inputs in a loop. I found that TTL levels from ATmega168 are enough to control the device without the need to use any TTL converters or additional transistors

Next steps

I think I will try to use ESP32 for the same purpose and will find an Android application to control the device from the smartphone if needed. Also will look for the replacement of the original remote control which is smart enough to learn or program all codes I found. There are power sockets on the backside, so it should be trivial to add some 5v PSU to control have it running. Maybe later will also do some XMBC integration to make it feel more native. Maybe I will also add decoding functionality to my gateway to understand commands from other RC-s. I tried to use decode functions from the Arduino-IRremote but they are not working properly, likely due to the same difference as with sending.