Adding web based remote control to my Marantz amplifier

In one of my previous blog posts I explained how to emulate Marantz remote control with Arduino using "remote in" socket. Now I decided to do something useful about it. My final goal is:

• Allow managing a device from any mobile or tablet
• Automatically power off the device if needed (e.g. at 4 AM)
• Could also be used for alarm functionality
• Better integrate with other devices, e.g. to turn on the radio if "Tuner" input is selected

Implementation

To support WIFI and be able to run a web server I decided to use the ESP32 platform, which is widely available and supported by Arduino IDE. Initially, I tried to connect GPIO12 output directly to the "Remote In" socket. This was working fine but completely blocked IR. So I had to add a diode, to avoid current from the amplifier to the ESP32. This solved the problem. As a power supply, I am using an old mobile charger with micro-USB output.

To implement HTTP i am using ESPAsyncWebServer project. Web UI is done using simple HTML/CSS/JS.

One of the early problems I found was that connection latency was very unstable, from 10 to 100ms. It was solved when I disabled power saving on the wireless interface, now it is within 1-5ms.

Source code

Source code is published in my github repo. To compile it – add spressif/arduino-esp32 and ESPAsyncWebServer manually.

Screenshot

To do

Something I may add in the future:

• Web interface for the sleep timer
• Maybe also wire device status to the ESP32. This would require some modification of the amplifier, so not sure if I want to do it.
• MQTT for the better IoT integration
• May be OTA, just to learn how it should work

Comments are welcome

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.

Sample of the decoded RC-5 command (“CD Input”)

Same from oscilloscope

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.

ESP32 based old clock controller, with NTP sync

I have been able to find an old “slave” clock from 1960 (according to the serial number).
It is Pragotron PJ 27, 12V version. They have been produced in Czechoslovakia during
196x years and using the PS-1 mechanism.

This type of clocks usually been used in organizations with central time management systems, e.g. schools, factories, etc. To drive them initially big mechanical “master” clock has been used, later such systems been replaced by digital one.

The clock mechanism is very simple and expects 1m impulse with different polarity on every run to move the arrows. There are also 6V, 24V, and 60V versions.

Making new clock controller hardware

After cleaning up clocks from the dust I tested them with a 12V power supply and found
that they are still working. As I don`t have any master clock to drive them – I
decided to build my controller. I had already an ESP32 controller with an OLED screen
on-board, so decided to utilize it. Also, I found a 220V → 12V/1A power supply left
from another project.

To generate 12V impulses with different polarities i decided to buy L298N DC Motor Driver Module.
It should be more reliable compared to a set of relays, polarity could be set using
TTL inputs and the module itself is very cheap (1-2$). Also, it provides a 12v → 5v converter,
so we can power our ESP32 board from it. I am currently using only one channel to drive clocks,
the second channel could be used for the alarm or clock in a different timezone.

Wiring, in this case, was very simple: 12V is wired directly to the L298N controller, 5V L298N
output and GND → to the ESP32 5V and GND, and L298N IN1 and IN2 are connected to the GPIO
pins 12 and 13. Clocks are connected to the L298N OUT1 motor output.

Software part

As ESP32 does not have real RTC I decided to use NTP over WIFI as a precise time source. This way I can avoid using an additional RTC module with battery.
To store slave clock status I am using ESP32 flash. I built software for the controller
using the Arduino IDE. Some of the features implemented:

• On boot, it connects to WIFI and using NTP to get actual time. After initial sync
  time is updated from NTP every 5 minutes.
• Timezone support is implemented using Timezone.
• Actual time, slave clock status, wifi status, and NTP sync status is displayed on the OLED screen.
• There is a special “init” mode which is enabled by touching GPIO15 and reboot.
  In this mode, impulses are generated every second. When the slave clock set to 12:00
  the pin needs to be released. This mode is useful for the initial setup or testing of the slave.
• State is saved every minute to the ESP32 Flash using the “Preferences” library. It is requesting
  “nvs” partition which implements basic wear leveling. To make it more efficient I changed the NVS partition size to 1Mb.
• To avoid OLED degradation in a 10m screen goes to the “screen-saver” mode. To exit screensaver – touch GPIO15 pin.

Code is available on the samm-git/clock-controller-esp github repo, comments are welcome.

Summary

It was an interesting journey to add NTP and wifi support to the device from 1960.
I was able to find a case from the old-time relay which now hosts my controller.
Maybe in the future, I will add more devices to this master.