Talk to your old CD Player

Have you ever wondered why you should buy new devices just because the old ones don’t support IoT? Any device controlled by an infrared remote can be transferred into an IoT device with a Adafruit ESP8266, an infrared receiver and LED, and your remote control. With the help of an IR code library, I was able to make a program that does just that.

Triggered with the phrase “Hey Google”, the Google Assistant is able to feed the words following the trigger phrase into its database of applets, one of which is IFTTT. Once one of the applets recognizes the phrase, it responds with a statement showing that it has acknowledged the command. In this case the answer phrase is set by the user. The Google Assistant will respond by saying the term set in IFTTT. I set it to “IR Code Sent.” The conversation will be something like the one shown in the conversation above.

Problem analysis

Our goal is to teach the Google Assistant to control a device with an IR signal. In this case we use a Panasonic SC-HC20 CD player.

We need a device, controlled by Google Assistant that can mimic an infrared remote control. In this project we will try to build that device and hook it up to Google Assistant using IFTTT (If This Then That). We build this so people do not have to buy new devices just so they can be controlled by “smart” devices.

Design considerations

We will give an overview of what we found and explain some of the trade-offs that we made.

Teaching Google Assistant skills

Google Home in classroom learning new tricks

Adding Skills to the Google Assistant can be challenging, but IFTTT simplifies the process by setting up the api.ai (Google’s Voice Recognition Platform) part of the equation. This was normally the tricky part of teaching the Google Assistant, and IFTTT makes this much simpler. Now all we need to do is configure IFTTT and code the transmitting device.

If This Then That (IFTTT) adds custom voice commands to Google Assistant and can sent information to a device using HTTP
Actions on Google adds a dialog to Google Assistant and supports sending and reading information to/from devices.

Infrared Interface platform

We need to make a device that can accept commands over WiFi and relay them as infrared commands to the CD player.

Requirements: small, low power, WiFi, GPIO (general purpose i/o pins)
Contestants: Arduino, ESP8266, Arduino 101, ESP32
Winner: Adafruit Feather Huzzah ESP8266. 1 MByte flash enough for over the air updates. Micro USB for code upload / debugging.Y

Infrared Interface infrared codes

Our device needs to be able to mimic the remote as to control the CD player.

Requirements: must support the platform; it ideally should recognize the device codes so we don’t have to use raw IR timings.
Contestants: A fork from Chris Young’s IRlib;
Winner:A fork from Chris Young’s IRlib;

Traversing the WiFi router

The access router in our home is a jack-of-all-trades. Among its many duties it protects the home network from outside intruders. This comes with a catch: Google Assistant needs access to our home network to control the CD player. This means we need to provide a mechanism in which Google Assistant can contact the CD device.

Like with anything else on the internet, there are many choices to consider. The two trains of thought are:

Make an exception in the firewall to accept and forward incoming commands to the IR interface. We can also use this router to handle the more resource intense encryption and scrutinize the commands to prevent code injection. Problem is that anything on the internet can access our webserver, so we need an authentication mechanism. There are two protocols that come to mind: HTTP and MQTT. HTTP is the protocol that brings the web pages that you visit to you. We can use it to push messages from Google Assistant to our IR interface. The other protocol, MQTT, is designed to provide low latency, assured messaging over fragile networks and efficient distribution to one or many receivers. It is less known but powers Facebook, and is supported by AWS IoT.
Maintain a connection to a web service, so that it can send messages to the IR interface over that existing connection. When using the HTTP protocol, we need a kludges like long polling or websocket. A more elegant solution is Firebase Cloud messaging, but that requires a substantial amount of memory to handle HTTPS and identifiers. It appears to run on ESP8266. The memory is used for HTTPS, UID and authToken. Problem is that it causes a lot of idle traffic and requires an intermediate server (because IFTTT doesn’t support it directly).

IoT devices are characterized by a small processor, little memory and low power usage. In this respect MQTT would be ideal. However, this requires a bridge such as Ponte or web service to translate between HTTP and MQTT. Instead, we decided to go with the more common HTTPS protocol.

Design, development and unit testing

The design consists of various blocks as illustrated below. We will describe the design, development and the unit testing for these blocks. We will start the Infrared Interface and work our way up to integrating it with the Google Assistant ecosystem.

All code is available through the repository:

Infrared Interface

We go straight to the exciting part: the infrared interface.

Design

The hardware for this project is straightforward. The microcontroller is an ESP8266-based Feather HUZZAH that already has an USB interface for programming and debugging.

The software uses a framework that provides: online WiFi SSID/passwd configuration, saves fatal exception details to non-volatile memory and supports over-the-air (OTA) software updates.

Development

The ESP8266 is connected to an Infrared Receiver to decoding signals from the original remote control of the CD player. To send infrared codes to the CD player it uses a transistor to drive an IR LED.

Hardware

Schematic of WiFi/IR interface — WiFi/IR interface schematic

Build the circuit as shown in the schematic above.

Gather the parts shown in the table below. Be careful to use the PN2222A or 2N222A transistor (not the P2N2222A).

Label	Part#	Description	Information	We paid
IR1	Vishay TSOP38238	Infrared Receiver 38kHz	datasheet	$ 1.08
D1	Everlight EL-SIR333-A	Infrared Diode 875nm 1.5V_drop	datasheet	$ 0.39
T1	PN2222Atfr	NPN Transistor	datasheet	$ 0.49
PCB1	Feather HUZZAH ESP8266	Microcontroller board	detail	$ 16.95
R1	1kΩ ¼W	Resistor		$ 0.02
R2	68Ω ¼W	Resistor		$ 0.02
	Feather Proto board		detail	$ 4.95

Assemble the circuit using a breadboard or prototyping board. The illustration below shows the pinouts.

Semiconductor pinouts
Test T1 and D1. Disconnect R1 from the ESP8266 module, and connect it to the 3.3V rail to verify that the voltage drop over R1 is approximately 3.4 V, indicating that the current through the infrared diode is 3.4V/68Ω=50mA. Reconnect the resistor to the ESP8266. Alternatively you can use camcorder to view the infrared light.
Note that we used the 5 Volt rails (labeled USB to supply the Infrared LED with sufficient current.

We assemble it for prosperity on a prototyping board

Software

When IFTTT makes the web request via Webhooks, the host of the website, in this case an Adafruit Huzzah Feather ESP8266 receives the command, and checks the command against its list of valid commands. If the command checks out, then it is matched to the corresponding IR command. It then sends the value out to the CD player, which completes the action.

Prepare your Arduino IDE or Microsoft Visual Studio environment. Install the board support and libraries listed in the table below.

IDE, board support and external libraries
Type	Component	Author	Version tested
IDE	Arduino	arduino.cc and community	1.8.5
Board support	ESP8266	esp8266 community	2.4.0
Library	WiFiManager	tzapu	0.12.0
Library	ESP8266 Framework	Coert Vonk	1.0.0
Library	ESP8266 Fatal	Coert Vonk, forked from Krzysztof	1.0.0
Library	IRremoteESP8266	Sebastien Warin et al.	2.3.1

Training is required so that the device issues the correct infrared codes to the CD player. to capture the infrared codes from the existing remote control, we used the example IRrecvDumpV2 from the IRremoteESP8266 library.
1. Compile and upload it to the device over USB Serial, then open the Serial Monitor.
2. Press the relevant buttons and note the button pressed and codes generated. E.g. for my CD player it shows the the manufacture’s address as 0x4004 (Panasonic) and the code for “play” as 0x05505005.
Program the device using the code from GitHub.
1. Copy or clone ir-interface.c.
2. Update the code with your own codes.
3. Compile and upload it to the device over USB Serial. Subsequent uploads may be performed using over-the-air (OTA) updates.
4. The first time the board starts up it will be in Access Point mode. Use a computer or phone to connect to WiFi network. If it doesn’t automatically connect you to the device, use a browser with any address. Use the browser to configure your networks SSID and password. These values will be saved in EEPROM so next time the device can connect directly.
5. Open a serial monitor and note the IP address assigned to the device.

Unit testing

Test the webserver pointing a webbrowser at http://ir-interface.local/ir/ir. You should see the infrared menu.
Test a keyword by pointing a webbrowser at e.g. http://ir-interface.local/ir?req=play. The CD player should start playing. The image below shows the pulse train on an oscilloscope

Infrared pulse train
Test the remaining keywords

Access router

The design relies on the router as an integral part of the solution. It functions as a remote proxy and translates between HTTPS used on the internet and HTTP on the local area network.