1. Compatibility
2. Motivation
3. Hacking the SB-H20
4. Building your own WiFi remote control
5. Contributing
6. Licenses and Credits

This projects was originally designed for the Intex PureSpa SB-H20. It is reported to work with the Intex SimpleSpa SB–B20 but is not compatible with the Intex SSP and SJB models.

Reading the user manual of the Intex PureSpa SB-H20 was a mistake. Everyone who has ever read a user manual knows this. They just contain things you don't want to know.

This model seems to be designed for daily attention. It is no news that the water of a pool should be run through a filter once or twice a day. Many pools have a timer for this, but not this one.

You could keep the circulation on permanently, but this has at least two disadvantages: The filter must be cleaned or replaced more often and you waste more than 1 kWh per day with the filter pump consuming around 60 W.

Somehow it should be possible to add a circulation pump timer. And if this can be done then the water temperature could also be controlled, thus combining power saving and comfort. Depending on the temperature profile you choose the energy saving can be really significant compared to a constant temperature setting because the heater consumes around 2 kW.

Opening the lid of the control panel and attaching a WiFi MCU in parallel to the buttons was the first idea that came mind. This was possible with the predecessors of this model, but not so with the control panel of the SB-H20. After testing around the edges of the case with my pry tools it became obvious that the lid is probably glued shut. If you want to open it anyway you might consider drilling holes into the sides of the case first to get better leverage for prying but I did not want to go that way.

Opening the pump unit and modifying the mainboard did not seem to be a good alternative either. But there is a cable between the pump unit and the control panel that might be tapped. Looking around I found the project diyscip from Geoffroy Hubert that gave me hope. Geoffroy did a splendid job with his reverse engineering but his project is about the SSP and SJB whirlpool models.

Using a multimeter, a scope and a logic analyser helped to establish several facts:

• there seems to be a good enough isolation between the mains and the signal lines (no guarantee whatsoever)
• the plug and the pinout of the SB-H20 control panel are identical to the SSP and SJB models
• most of the decoding of the signals from the mainboard to the control panel is identical or at least similar to the SSP and SJB models
• the original control panel and an additional remote control unit can be attached in parallel to the mainboard because the signalling supports a multi-drop architecture for listening
• the button signalling from the control panel to the mainboard seems to be completely different from Geoffroy's description

Getting all the details right for this last aspect took a while. With the SB-H20 data clock of 100 kHz it was like searching for a needle in a haystack. To get 20 data points per clock cycle you need to run the logic analyser with 2 MS/s and this results in 4 million data points for the 2 seconds it takes to press and release a button on the control panel. Programming an ESP8266 MCU to provide a hardware trigger for the logic analyser was the key to narrow down where the action takes place: the control panel pulls the data line low for about 2 µs after a specific button scan data word was received from the mainboard and this signalling must be repeated until the mainboard confirms the button action by enabling the display beeper.

Because of this difference between the Intex models it is not possible to use Geoffroy's schematics and code for the SB-H20. After testing several variants the required behaviour could be achieved with a much simpler circuit, that mostly consists of an ESP8266 and a TTL level shifter for the 3 signals.

For the button signalling to work the ESP8266 must be running at 160 MHz to get the timing right, but that is not all. Geoffroy documented in his code that the interrupt driven data receive is unreliable but he did not name a reason. The reason is that the ESP8266 WiFi processing has precedence over all other MCU tasks and will disrupt time critical processing including ISRs. This is acceptable for the data receive because the data repeats at a high frequency. Incomplete frames can be ignored and invalid frame data can be filtered out by using only repeated identical data. But during the button signalling a receive error causes side effects. A single button press might be ignored or may cause a double change. With multiple consecutive button presses the error probability increases significantly. To prevent this I decided to activate the ESP8266 WiFi modem sleep when changing the water temperature. This improves the reliability noticeably but the ESP8266 looses its connection to the AP and the MQTT server for a few seconds.

So far the SB-H20 was not modified. To keep it that way an Intex control panel extension cable is needed to insert the WiFi remote control but I could not find a source. If you have access to a 3D printer you should have a look at this 3D model. Otherwise you need to cut and tap the cable from the control panel to the main board.

⚠️ WARNING: If you decide to continue you will void your warranty for the SB-H20. You may only USE THIS PROJECT AT YOUR OWN RISK. I do not provide any warranty and I will not assume any responsibility for any damage you cause yourself or others by using this project.

Depending on your preferences you have several options available regarding the PCB:

• use a perfboard (the ciruit is rather simple)
• use the PCB design from @Elektroarzt
• create you own customized PCB

It is not even essential to use the D1 mini, it just makes uploading the firmware and the config file easier because you don't need an extra USB adapter and a 5 V DC converter is also included. Any other ESP8266 board with enough ports on the breakout will do (e.g. ESP12, HUZZAH) but may require slight adjustments to the circuit.

Before you make a final decision about the board type read the chapter about the thermometer below.

Select a case that is IP64 or better to protect the circuit from moisture and to protect the pool users from electrical shock. The same applies to the cables and plugs. For my solution these components were the most expensive part of the project at around 30 EUR.

This project will tap the 5 V DC power supplied by the SB-H20 mainboard to the control panel. Using this power source avoids electrical hazards that may be introduced by adding an additional mains power supply. A battery might be an alternative, but with a typical power draw of 20 mA you need a rather large power pack for a month of continuous operation.

The 20 mA apply if the ESP8266 is able to enter auto modem sleep mode and for this the communication from and to the ESP8266 must be idle most of the time. The periodic MQTT publish will interrupt this idle state only for a very short time with a consumption at 70 mA. The power on current of the circuit is almost 100 mA and if you have a lot of WiFi traffic addressing the ESP8266, e.g. broadcasts, the consumption might stay at 70 mA.

Beware that the power reserve of the SB-H20 mainboard is unknown and that's why I added a fuse. It is still possible that the extra load of the WiFi controller may overtax or damage the mainboard. With a consumption of 20 mA the probability is rather low because a single segment of a 7-segment display alone will consume a few mA and not all segments are on all the time but the power supply of the SB-H20 should have the reserve for this case.

Build the firmware using the Arduino IDE with the board settings documented in the INO file and flash the MCU. Note that the firmware uses DHCP and the MQTT server is addressed by hostname. If you prefer static IPs you must modify the firmware appropriately.

Edit the example configuration file config.json in the subdirectory data. If you install the Arduino ESP8266 LittleFS Filesystem Uploader you can use the Tools menu of the Arduino IDE to upload the content of the data subdirectory to the MCU.

Example:

{
  "wifiSSID": "WiFi-SSID",
  "wifiPassphrase": "WiFi-secret",
  "mqttServer": "mqtt.at.home",
  "mqttUser": "leave blank if you don't need authentication",
  "mqttPassword": "leave blank if you don't need authentication",
  "mqttRetain": "no"
}

If mqttRetain is omitted the MQTT messages will be published without the retained flag set. If defined all values except "no" will activate retaining.

All other config values are mandatory. If you get a parsing error in the serial monitor when starting the MCU look closely into your config file. Maybe you missed a quote or a comma somewhere.

Prepare your MQTT server for a new device.

Published Topics

The topics will be published once after the connection to the MQTT server is established and then only on change except for the topic intex/state, with a change rate limit of 1 per second.

Subscribed Topics

The pool topics are equivalent to the buttons on the control panel of the SB-H20. Refer to the user manual for more details.

Wait for the next update of the equivalent published topic after each command and use a timeout to detect command failure. The SB-H20 control panel can only handle one command at a time. The duration for changing the water temperature depends on the temperature delta.

If wifi/state is error you are only allowed to send the command pool/command/power=off. The SB-H20 will continue to beep for a while. To clear the error it is necessary to power down the SB-H20.

The circuit comes with a NTC sensor for measuring the temperature inside the waterproof case. The ESP8266 is said to be rather robust (-40 °C to 125 °C) but this way you are able to monitor the case temperature.

It cannot be avoided that the temperature inside a sealed case will be much higher than the ambient temperature. For proper heat dissipation the metal case of the ESP8266 could be attached to a heat spreader. But your options are limited because you need a plastic case for good WiFi reception and electrical isolation.

The default settings in the code provide an accuracy of approximately 1 °C at room temperature and this should be good enough for most use cases.

If you need a higher accuracy you can calibrate the thermometer by providing the following 4 values that should be measured with a mulitmeter with at least 3 digits accuracy:

ESP module not attached to circuit and not powered on:

• Re: resistance between ESP module A0 and GND
• Rt: resistance between ESP8266 A0 and GND
• Rr: resistance between NTC and GND

circuit powered on:

• Vr: supply voltage at NTC

Insert these values into the thermometer setup command in the INO file:

 thermometer.setup(Rr, Vr, Rt/Re);

Some ESP modules do not come with a voltage divider for A0 (Re and Rt > 1 MOhm). In this case you need to add your own voltage divider because the ESP8266 analog input is limited to 1 V.

Connect the WiFi controller to the SB-H20. Verify the pinout before powering up the pool. After power up the control panel should operate normally. The WiFi controller should connect to the AP, receive an IP address and connect to the MQTT server within a few seconds. If this was successful it will report the current status of the pool to the MQTT server.

In case of an error you should check the logs of your AP and your MQTT server. If the WiFi controller connects to the MQTT server successfully but reports offline state you should check the pinout again, preferably with a scope. If this does not help you should use the serial monitor of the Arduino IDE and you can activate additional serial debugging in the firmware.

Security aspects are typically not the focus of a DIY project and the basics for the electrical security have been mentioned above.

Regarding the network security of the project you will notice that it does not include a webserver. At first glance this seems to reduce the usability. But you need the Aruduino IDE anyway to build and upload the firmware and uploading the config file with the Arduino IDE as a seconded step is seamless. And if you want a webserver anyway it would be easy to add.

But not enabling the webserver is a security improvement because it is nearly impossible to harden the webserver on an IoT device. That is why the project only uses TCP/IP clients with predefined servers: One is the MQTT client and the other is the OTA client. In this configuration a hacker must take over significant parts of your network and if he got so far then he cannot be stopped anyway if he knows what he is doing.

So just make sure that your MQTT server UI is secured properly and you will not find your pool cover blown off because a guest turned on the bubbles while the cover was closed.

One up would be to use encryption for the MQTT communication but the MQTT client library currently does not support it.

If you want something clarified or improved you may raise an issue.

Copyright (c) 2021 Jens B.

The code was edited with NetBeans.

The firmware was build using the Arduino IDE.

The schematic was created using KiCad.

The signal analysis was aided by PulseView.

The badges in this document are provided by img.shields.io.

The firmware source code depends on the following projects:

Copyright (C) 2015 Arduino Core for ESP8266 Project

Parts of the "Arduino Core for ESP8266" project have different licenses, see the project description for more details.

Copyright (C) 2014 Benoît Blanchon

Copyright (C) 2017 Arm Limited

Copyright (C) 2008 Nicholas O'Leary

The concept of this project and parts of the firmware are based on:

Copyright (C) 2020 Geoffroy Hubert

Copyright (C) 2022 Elektroarzt