WARNING 1 : The circuit in this project uses main voltage (220-240 Volt AC in western Europe). This can be deadly if not handled properly! You can easily hurt yourself as well. Build this circuit at your own risk.
WARNING 2 : Never ever ever power this circuit directly without a GFCI outlet (differential circuit breaker). Remember this wircuit will be used in a wet environnement. If you don't understand this, please watch this video https://www.youtube.com/watch?v=SHGo-52wCDc&t=63s and get some electrical knowledge about ground protection.
WARNING 3 : This project is still a work in progress, this page is a kind of building log, I haven't finish the board building and installation for the moment. Watch the issues page to see what is working and what is not.
This project aims to build a replacement for the motherboard of the Intex SSP-20 Spa (it may work with other Intex spa and could be used to build a spa from scratch, but this is not the purpose of this page). My goal was to be able to control the spa remotely and integrate it in my domotic system. I'm using Jeedom https://www.jeedom.com/ as a domotic system, an open-source system, but it should work with other system since the communication part of this board will rely on MQTT protocol and a rest server (based on the Arest library - https://github.com/marcoschwartz/aREST). The second goal of this project is to improve the reliability of this spa and specificaly to solve a random E95 or E9X error problem. My spa was still under waranty when i started this project so I tried to be as stealth as possible.
Below the annotate picture of the motherboard with my understanding of its working principle. Since the card is labeled, everything is pretty straight forward except the descaler system and the pump system (the upper terminal barrier connector on the board).
There are 5 sensors connected to the board, 2 temperature sensors (black and white connectors), 2 flow sensors (red and green connectors) and 1 temperature fuse (yellow connector). They are all connected with a 3 pins JST like connector (it looks like a JST XH 3P but the JST XH 3P doesn't have a lock mecanism).
Both temperature sensors are negative temperature coefficient (NTC) thermistore, it means that the resistance of the thermistore decreases with an increase in temperature.
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The temperature sensor 1 is installed at the intake of the water pump so it reads the water temperature and it is use to regulate the water temperature from 20°C to 40°C.
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The temperature sensor 2 is installed in the core of heating elements and its function is to detect overheating over 50°C and shut down the heating if necessary.
Since I'm reading a resistance value and not a temperature, I need to do some calibration (i.e. find a relation between the resistance I'm measuring and the temperature). To measure the real temperature of the water in the spa I connected a DS18B20 thermal sensor in place of the LCD panel. Then I have recorded the temperature of the water and the resistance of both integrated temperature probe of the spa during the heating process of the spa from 18°C to 40°C. The resut once smoothed is the curve presented below. (smoothing is mandatory since the ADC of the ESP32 is pretty noisy...)
I first tried to use the Steinhart-Hart equation https://fr.wikipedia.org/wiki/Relation_de_Steinhart-Hart but O did not get good results using this equation, especialy from 34 to 38 degrees.
Since I'm observing that the curve is pretty linear from 18 to 38 degrees, and that the value of the resistance is 0 for 40°C, I tried a linear regression. The result is pretty decent with a R=0,9926.
The equation is T = -276,38*R + 10513
You can also try a logarithmic regression an get the following equation : T = -7750*Ln(R) + 28589
One temperature fuse is installed just below heating elements. I cannot test the triggering temperature but it seems that in normal condition the fuse let the current pass and if the temperature goes over 84°C then the fuse burn and the current stop passing and shut down the heating.
Both flow sensors let the current pass only if flow is detected, they ensure that no heating is activated if there is no flow detected in the system.
All the power cable (input and outputs) are connected by a barrier terminal block. We will use the same connector on our board because we don't want to alter the power cable and change their connector.
There is two heating element in the spa for a total power of 2000 Watts. They are directly powered by a relay allowing 220VAC to pass trough the heating element. Please note that in normal condition :
- The water pump is always powered when heating. Any flow interruption signaled by the flow sensor result in an error and the heating stops.
- When you push the heating button the heating doesn't start immediately, the water pump starts and then a couple seconds after the heater 1 is powered then a couple seconds later the heater 2 starts.
- The heater 2 is shut-down if the jet pump is activated.
The jet pump is directly powered by a relay allowing 220VAC to pass trough the pump and pumping air into the Spa.
The water pump is powered by 12VAC but before that a relay allows 220VAC to flow through a dual output 12VAC transformer (see the drawing above). The first output is send to a closed relay and the second output of the transformer goes into a full bridge rectifier producing 12VDC send to activate the relay and let the 12VAC flow into the water pump. It seems that the only goal of this system is to allow the descaling system to start at the same time as the pump (see below the descaling system). On this version on the board we will not implement the descaling system (maybe on the next version) so we will power the pump directly from the output transformer. (connection of A and B wires to C and D wires)
I will replace the control panel with an external control box connected through the enclosure of the spa with an IP68 SP21-12 connector. (available here : https://www.amazon.com/gp/product/B071R6RSN6/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1)
It seems that this spa is equiped by a magnetic descaling system. Here is the wikipedia page on this technology (https://en.wikipedia.org/wiki/Magnetic_water_treatment). I cannot find the type of signal send to this device, it seems that the signal is AC with a modulation of amplitude. I will maybe investigate it later... so this function has not been implemented on the replacement board.
An ESP32 (DevKitc) is the heart of the system. It allows us to connect :
- 2 temperature sensors on 2 analog inputs,
- 2 flow sensors on 2 digital inputs,
- 1 temperature fuse on 1 digital input,
- 5 buttons on 5 digital input (PUMP, HEATING, JET, +, -),
- 1 LCD display on 2 digital inputs (I2C protocol),
- 4 power relays on 4 digital inputs.
Relays, LCD, temperature sensors, flow sensors, and buttons will not be powered from the 5 Volt pin of the arduino, we will use directly the 5 Volt DC power supply to power them directly.
The integrated wifi chip also allow us to connect to the wifi and the MQTT server to send and receive data.
I used Eagle 8.2.2 to design the replacement board, below is the electrical drawing. The eagle files will be available soon.
I wanted the board to be easily produce at home by anybody so I choose to use a single side PCB with plated-trhough holes (PTH) components. SMD component will be a also good choice, but I know that occasionnal welder are more at ease with PTH components. The drilling size is 0.8mm, the width of the electrical tracks is 16mil (0.40mm) and the clearance is 10mil (0.25mm), theses parameters allows you to produce the board using the toner transfer method (this method requires very few tools).
Relays are integrated on the board to be integrated more easily in the original enclosure.
The original motherboard dimension are 10.5 cm x 17 cm, mounting hole are 5mm wide and are placed 4.5mm from the edge of the board. The PCB will be mounted using the same mounting screw used by the original motherboard (but I don't think I will be using the center plastic lock).
The power tracks (tracks going to relays) will carry a lot of current. The total power of the Spa announced by Intex is 2200 watts. I have made some measurement on the original board to see how much current is use by each component :
- Heater 1 : 6.70A (Peak at startup) / 3.70A (Cruise) @ 220 Volt AC
- Heater 2 : 7.00A (Peak at startup) / 4.00A (Cruise) @ 220 Volt AC
- Water pump : 0.16A @ 12 Volt AC (This measure include also de descaler)
- Air pump : 5.50A (Peak at startup) / 3.60A (Cruise) @ 220 Volt AC
As we can see, if everything is running at the same time the spa can draw a total of 11.46A with a peak at startup of 19,36A which is a lot. In the original board there is some rules to avoid the spa to reach this high current drawing :
- Heater 1 and 2 have a 20 seconds startup delay between each other.
- Air pump and heater 2 can't run at the same time.
We will implement the same rules to our board so the maximum current draw will be around 8A with a peak around 11A when starting the heater or the pump. (Which is about what is announced by Intex around 2400 Watts). By dimension the track width for 10A, 2oz/ft copper, an ambiant temperature of 25°C and a maximum temperature elevation of 5 degrees, we find that we need a 2,36 mm (93mil) track width.
Board schematic has been sent to PCBway a chinese PCB prototyping company. https://www.pcbway.com/. They can even populate your board with the component if you want them to do it.
The list of component with links to buy them is provided below :
Open the lastest *.ino file within the arduino IDE and configure the following variables to your needs.
const bool wifi_enable = true;
const char* ssid = "YOUR_WIFI_NETWORK_NAME";
const char* password = "YOUR_WIFI_NETWORK_SECURITY_KEY"
Please note that in the current state of developpement you must activate WiFi in order to control the spa. The local commands are not working properly.
if you want to use mqtt you must set :
const bool mqtt_enable = true;
const char* mqttServer = "IP_OF_YOUR_MQTT_SERVER";
const int mqttPort = PORT_OF_YOUR_MQTT_SERVER;
Additionnaly you could set-up the topic that will be used by the control board :
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const char* mqttTopicTemp1 = "spa/temp1";-> will contain the temperature from the sensor 1 (read only) -
const char* mqttTopicTemp2 = "spa/temp2";-> will contain the temperature from the sensor 2 (read only) -
const char* mqttTopicFlow1 = "spa/flow1";-> will contain the flow detection from the sensor 1 (read only) -
const char* mqttTopicFlow2 = "spa/flow2";-> will contain the flow detection from the sensor 2 (read only) -
const char* mqttTopicHeater = "spa/heater";-> will tell you if the heater is enabled (read only) -
const char* mqttTopicHeartBeat = "spa/heartbeat";-> will contain the heartbeat of the spa, an integer updated at each loop (read-only) -
const char* mqttTopicError = "spa/error";-> will contain the lastest error from the spa (read only) -
const char* mqttTopicTarget = "spa/target";-> will tell you what is the current target temperature (bi-directionnal) -
const char* mqttTopicTempRegulation = "spa/temp_regulation";-> will tell you if the temperature regulation is enabled (bi-directionnal) -
const char* mqttTopicFiltration = "spa/filtration";-> will tell you if the filtration is enabled (bi-directionnal) -
const char* mqttTopicJet = "spa/jet";-> will tell you if jet is enabled (bi-directionnal)
if you want to use WiFi OTA (a very usefull feature that will allow you to upload any update of the code over the air, wihout opening the case) you must set :
const bool ota_enable = true;
Place your ESP32 on a breadboard and upload the code. Once the upload is finish press the reset button of the board.
Open the serial port monitor of the Arduino IDE and set the baudrate to 115200. You should see the start-up and the IP of your board on the WiFi network.
If you have any error message during the start-up you should check your board configuration.
Once the board is connected to the wifi network you should open the following URL : http://IP-OF-YOUR-BOARD.You should get a JSON chain giving you the current state of the board. It should looks like this :
{"variables": {"flow1": false, "flow2": false, "temp1": 0.00, "temp2": 0.00, "heartbeat": 65065, "target_temp": 20.00, "filtration": false, "heating": false, "temp_regulation": false, "jet": false}, "id": "", "name": "", "hardware": "esp32", "connected": true}
If you have set-up the mqtt server
Try to connect to : http://IP-OF-YOUR-BOARD/filtration?param=1. This is the command to activate the filtration. You should receive a response of this form : {"return_value": 0, "id": "", "name": "", "hardware": "esp32", "connected": true}. You can turn it off by sending http://IP-OF-YOUR-BOARD/filtration?param=0.
The list of the available command is :
http://IP-OF-YOUR-BOARD/filtration?param=0orhttp://IP-OF-YOUR-BOARD/filtration?param=1-> will enable or disable the filtration.http://IP-OF-YOUR-BOARD/jet?param=0orhttp://IP-OF-YOUR-BOARD/jet?param=1-> will enable or disable the jet.http://192.168.100.75/temp_regulation?param=0orhttp://192.168.100.75/temp_regulation?param=0-> will enable or disable the temperature regulation.http://192.168.100.75/target_temp?param=X-> will set the target temperature.
First, it is very important to DISCONNECT THE POWER CABLE of the Spa. Remove the four screws securing the spa cover and remove it. Then locate the cover of the control board, remove all the screws and remove the cover. On the control board remove all cable from the lower and upper terminal, from the sensors and from the control panel, then remove the four screws securing the board and remove it.
Remove the central plastic pin in order to install the new board into the enclosure and then install the new board using the 4 screws from the old board. Then connect the old cables on the new board. Here is a quick connection guide based on the color of my board (double check it with you board before powering up the spa) :
- Red connector -> Flow 1 connector
- Green connector -> Flow 2 connector
- White connector -> Temperature 2 connector
- Black connector -> Temperature 1 connector
- Yellow connector -> DO NOT CONNECT (it doesn't work currently)
- Connector 1 -> N terminal
- Connector 2 -> L terminal
- Connector 5 -> N of the pump terminal
- Connector 6 -> L of the pump terminal
- Connector 7 -> N of the jet terminal
- Connector 8 -> L of the jet terminal
- Connector 9 -> N of the heater 1 terminal
- Connector 10 -> L of the heater 1 terminal
- Connector 11 -> N of the heater 2 terminal
- Connector 12 -> L of the heater 2 terminal
Then you have to connect together some wires from the upper terminal and isolate all non connected wires before powering up the spa.
- Cable A must be connected with cable C
- Cable B must be connected with cable D
You should get something like that :
