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Project by Richard Palmer HomeAssistant Satellite using a Raspberry Pi Pico W » Analog and digital inputs and outputs » Can transmit infrared remote control codes » Includes a relay/LED driver » ESPHome supports hundreds of sensors and controls » Includes an I2C bus connector compatible with 2QWIIC, STEMMA QT, GROVE & PiicoDev » Remote configuration and management This simple board lets you connect lots of different kinds of sensors, displays and other things wirelessly to a HomeAssistant based Home Automation system. n a Home Automation system, sensors and actuators CON9, a 4-pin JST-SH connector that is compatible with Itions attach to ‘satellites’, which can be placed at different loca- QWIIC, Stemma QT, Grove and PiicoDev devices. CON8 around the home. Each can support multiple attached also provides access to the I2C0 bus, allowing the connec- devices communicating with the hub over the household tion of a small OLED screen. If two devices with the same I2C address need to be WiFi network. Our Satellite uses a Pico W microcontroller module pro- connected, a second I2C bus is available at several locagrammed with the ESPHome firmware. While the newer tions on the expansion connector, CON4. However, note Pico 2 W may be used, it costs a little more and the extra that pull-up resistors will need to be added if the second power is not required for this application. I2C1 bus is used. A small PCB hosts the Satellite’s The adjacent table lists the functions CON4 expansion header pinout basic components and makes it easy to available on the expansion connector. connect to a wide range of supported Pin Signals Separate pads for the 5V and 3.3V supdevices. You can see a list of the sup- 1 plies and ground are provided at CON1GP15, I2C1, SPI1 ported sensors at https://esphome.io/ CON3. 2 GP14, I2C1, SPI1 components For remote control, IR LED1 is driven 3 GP13, SPI1, UART0 by Q1, a BC817 or similar NPN transistor, Circuit description from the 5V supply. Its 40mA operating 4 GP12, SPI1, UART0 Fig.1 shows the Satellite circuit. current is higher than can comfortably GP11, I2C1, SPI1 As you can see, there isn’t a lot to it 5 be supplied directly by a digital output besides the Raspberry Pi Pico W mod- 6 pin on the Pico module. GP10, I2C1, SPI1 ule shown in the middle. Transistor Q2 can drive an off-board 7 GP9, SPI1, UART1 Most sensors and many control 5V relay or solid-state relay (SSR). LED2 GP8, SPI1, UART1 devices will connect to the Satellite 8 lights when the relay is operating, while via a two-wire I2C serial bus. I2C0’s 9 diode D1 protects the transistor against GP7, I2C1, SPI0 SDA (I2C data) and SCL (I2C clock) back-EMF when a traditional relay GP6, I2C1, SPI0 functions are connected to GPIO pins 10 switches off. GP28, ADC0 20 and 21, with pull-up resistors to 11 The 64kHz PWM signal at GP16 is the 3.3V rail as required for I2C com- 12 smoothed by an RC low-pass filter formed GP27, ADC1 munications. by a 10μF capacitor and 470W resistor, GP26, ADC2 Access to the I2C bus is provided by 13 giving a -3dB frequency of approximately 54 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.1: the Raspberry Pi Pico W module drives the IR LED (LED1) and relay through transistors Q1 and Q2. Digital and analog I/O is via CON4, with power available from CON1-3. CON9 is a QWIIC, Grove and PiicoDev compatible I2C connector. The I2C OLED display connects via CON8. 34Hz, reducing the ripple of a 50% duty cycle output to around 10mV peak-to-peak. While the Pico is capable of much higher PWM frequencies, which would result in even lower ripple, there is a trade-off between frequency and bit depth (resolution), which is 10 bits at this frequency. The smoothed output is presented at CON6, forming a basic kind of digital-to-­ analog converter (DAC). The board’s 5V supply is powered either via a microUSB cable plugged into the Pico W, or from CON5. In most cases, a 5V 500mA supply should be adequate, as the Pico W draws less than 100mA and the IR transmitter requires 20mA on average. However, the supply must also be able to support the needs of any connected devices. For instance, 5V relays commonly draw 75mA or more when energised. The Pico W module has an onboard 3.3V regulator capable of supplying 250mA to auxiliary devices. If more than this is required, an additional 3.3V supply will be needed. Construction The Satellite is built on a double-­ sided PCB coded 15104251 that measures 51 × 54mm. Start by soldering the SMD components in the locations shown in Fig.2. The band on the diode must point toward the power header. Next, add the two 20-pin female headers for the Pico, the JST-ST connector (CON9) and the two LEDs. Leave CON1CON8 off at this stage. Solder headers to the Pico W, if they weren’t already fitted, and plug it in with the USB socket at the top of the board. You can use the sockets on the board as a jig to hold the headers while soldering them to the Pico W. Now plug the USB cable into a port on your PC. 5V should appear on CON1 and 3.3V at CON3. Disconnect it after checking those supply rails. siliconchip.com.au Configuration If you have difficulty with any of the configuration steps below, there is documentation at ESPHome’s website (https://esphome.io) and a helpful user community at https://community.home-assistant.io Load the ESPHome firmware next. Go to the ESPHome Builder tab in HA, click on the + NEW DEVICE button and CONTINUE. You can name your device “myHome” (or something else if you prefer). Select Raspberry Pi Pico W as the platform, then click INSTALL. A copy of the encryption key will be saved in the configuration file. Select the “Manual download” option when the pop-up window appears – see Screen 1. It will take a minute or more for HA to compile customised code for the new device. When the wheel stops spinning, select Download project and UF2 factory format, then close the pop-up window. You may need to approve the download in your browser (“Keep” in Chrome) as it’s coming from an unsecured host. Hold down the BOOTSEL button on the Pico while plugging its USB cable into your computer. Copy the downloaded UF2 file across to the “RP1-RP2” drive that has appeared in the PC’s file manager and close the pop-up window. Fig.2: all components are on the top of the PCB; mount the SMD components before the through-hole items. Australia's electronics magazine September 2025  55 The block with your Pico’s name should become ONLINE in the ESPHome Builder tab, after a 30 second delay (Screen 2). This is a basic ESPHome device, with no sensors or outputs configured. Click on the EDIT link on the myHome card and the configuration file will be displayed. Additional configuration lines for sensors and controls will be added below this code – see Screen 3. Screen 1: the “New device” screen while the code is being compiled. Each YAML block starts with an identifier, usually the item’s type. Values are indented and the number of leading spaces is significant (usually two per level). Each level’s information is terminated when a less indented item is encountered. Comments begin with a “#” and continue to the end of line. Close the editing window by clicking the X at the top left corner and click on the LOGS link in the myHome card. A window will open with the history of the device since it was last booted. In this case, most of the information is in purple, describing the WiFi connection process. Close the window. The Satellite is now ready and the final step is to tell the HA Core that it exists. Go to Settings then Devices & services and +ADD INTEGRATION. Search for “ESPHome” and click SUBMIT. The Satellite should pop up as a discovered device. If not, type “myHome.local” (or prefixed with whatever name you gave it) into the “Host” field and click SUBMIT. If you had to enter the host name, the installer will ask for the encryption key from the myHome.yaml configuration file. Click SUBMIT after that. The Area field may be left blank on the next screen. Approve the request for the device to perform HomeAssistant actions, then click FINISH to make the Satellite active. The Satellite may not appear on the Overview dashboard at this stage, as it has no sensors or controls defined. Adding a sensor Unplug the USB cable, connect an SHT40 temperature sensor to the I2C port and plug the USB cable back in. Re-open the editor and add the following code at the bottom of the myHome.yaml file. Screen 2: the initialised Pico W Satellite’s card in the ESPHome builder tab. ## Temperature.yaml ## Temperature & Humidity sensor ## Pico W I2C0 bus i2c: sda: 20 scl: 21 scan: true frequency: 400kHz ## SHT40 sensor sensor: - platform: sht4x update_interval: 10s humidity: name: “Humidity” id: humidity temperature: name: “Temperature” id: temperature Screen 3: the myHome device’s initial configuration file. 56 Silicon Chip Rather than typing this in, you can copy and paste this from the file named “Part2.yaml” in the download package for this series (siliconchip.au/Shop/6/2482). That will not only save time but ensure you get the correct formatting for it to work. The first section defines the I2C bus that will be shared by other connected devices. The sht4x ‘platform’ uses the defined I2C bus by default. The “name:” field is used when displaying the entity, while the “id:” field is required if the entity is to be referenced by code. Australia's electronics magazine siliconchip.com.au In the SHT40 section, humidity and temperature sensors are defined, and the interval between readings is shortened from the default value of 60 seconds to 10. After adding the code, click SAVE and INSTALL (in the top right-hand corner) and select the Wirelessly option in the pop up. Depending on your HA setup, compiling the code may take a minute or more. You will know it has finished when the green SUCCESS message appears in the log. The code will then attempt to upload to the Pico and, after a delay of thirty or more seconds; the screen will show the Pico’s boot log. At the bottom should be light blue text indicating that temperature and humidity readings are being sent to the HA hub. If your configuration won’t compile, it may be due to incorrect indentation or code in the wrong location. The window may be closed by clicking STOP at any time after the download has completed. While STOP may appear a strange command to close the window, HA has launched a virtual Docker machine to do this work, and stopping the virtual machine when it is no longer needed closes the window. Close the myHome.yaml edit window, then go to HA’s Overview dashboard. After a minute or so, the myHome card should appear, showing the temperature and humidity. If it doesn’t, try reloading the web page. Screen 4: the myHome dashboard card with the Relay LED. The SSD1306 display showing temperature, humidity and the state of the Relay LED. Controlling the relay and LED Only a few extra configuration lines are needed to map the relay driver’s GPIO pin as a switch output. They are added to the Satellite system’s myHome.yaml configuration file below the SHT40 sensor definitions. The “switch:” component indicates that this is a binary output. The GPIO platform then maps the function to a microcontroller pin: ## Relay_LED.yaml ## Pico Relay and LED switch: - platform: gpio pin: 22 name: “Relay LED” id: led Save and install the updated configuration. After a minute or so, the myHome tab on the Overview dashboard should include a switch for the Relay LED – see Screen 4. Toggling the switch should cause the LED to come on. The completed Satellite board with and without the Pico W. All components are mounted on the top of the doublesided PCB. The optional header pins at CON8 allow easy disconnection of the OLED display. Adding a display ESPHome supports a wide range of displays. The SSD1306 OLED used in this project has an I2C interface and we can use it to show the current temperature and humidity, along with the LED/relay state and a graph of temperature over time. The display can be daisy-chained with the temperature sensor or connected via CON8. When wiring it up, take care with the pinouts as they tend to vary between display manufacturers. The I2C bus is already defined, so all that is needed is to declare the OLED display and add some lines of code to run regularly that write to the display. The OLED screen is set to the standard I2C address for 128×64 pixel mode. As the built-in font is blocky, we can use some Google fonts instead. In the display section of the code below, there is a portion siliconchip.com.au Australia's electronics magazine September 2025  57 Parts List – Home Assistant Satellite 1 double-sided PCB coded 15104251, 51 × 54mm 1 Raspberry Pi Pico W module with two 20-pin headers (MOD1) 1 micro-B USB cable 2 20-pin single-row female header sockets 4 3-pin headers (CON1-CON3, CON7) (optional) 1 13-pin header (CON4) (optional) 2 2-pin headers (CON5, CON6) (optional) 1 4-pin header (CON8) (optional) 1 4-pin JST-SH 1mm-pitch socket (CON9) [Core Electronics PRT-14417] Semiconductors 2 BC817 NPN transistors, SOT-23 package (Q1, Q2) 1 5mm 50mA IR LED (LED1) [Altronics Z0880A, Jaycar ZD1945, Core Electronics ADA387] 1 3mm red, yellow, amber or green LED (LED2) 1 SS14 or similar 1A schottky diode, DO-214AC/SMA [Altronics Y0084] Capacitors 4 10μF M2012/0805 16V X7R Resistors (all SMD M2012/0805 size 1%) 3 2.2kW 2 1kW 1 470W 1 100W Add-on sensors & display used in this article 1 SHT4x QWIIC temperature and humidity sensor [Core Electronics ADA4885 or ADA5776] 1 QWIIC cable [Core Electronics CE07773, Altronics Z6596 or Z6597] 1 AM312/AS312 PIR sensor module [Altronics Z6382A, Jaycar XC4444, Core Electronics CE05786] 1 SSD1306 I2C OLED display [Altronics Z6525, Jaycar XC3728, Core Electronics CE09493] marked “lambda”. Any code following the lambda marker is passed to a command interpreter for execution at runtime. Lambda code is written in the C language. Add the code to myHome.yaml below the relay’s “switch:” definition block: ## OLED_display.yaml ## define the fonts font: - file: “gfonts://Roboto” id: roboto_12 size: 12 - file: “gfonts://Roboto” id: roboto_16 size: 16 ## graph configuration graph: - id: temp_graph sensor: temperature ## sliding time window duration: 60min width: 106 ## half display height height: 32 border: True max_value: 40 min_value: 10 y_grid: 10 ## SSD1306 display display: - platform: ssd1306_i2c model: “SSD1306 128x64” address: 0x3C ## Print the text and graph lambda: |it.printf(0, 0, id(roboto_16), “%.1f°C %.0f%%”, id(temperature).state, id(humidity).state); if (id(led).state) { it.print(0, 14, id(roboto_16), “ON”); it.filled_circle(44, 22, 6); } else { it.print(0,14, id(roboto_16), “OFF”); it.circle(44, 22, 6); } it.print(110, 30, id(roboto_12), “40”); it.print(110, 52, id(roboto_12), “10”); it.graph(0, 32, id(temp_graph)); As with other YAML code, the lambda block ends when less indented text is found. The version in the download pack is easier to read, as the lines haven’t been wrapped to fit into a magazine column. The lambda code prints temperature and humidity on the first line, with the state of the LED and a circular on/ 58 Silicon Chip Australia's electronics magazine siliconchip.com.au Screen 5: the Traces screen for the “AC off” automation. off indicator on the second line. The bottom half of the screen displays a graph of the temperature over the past 60 minutes, between 10°C and 40°C, with horizontal grid lines every 10°C. The state of the relay LED slider on the dashboard (Screen 4) should be reflected in the OFF/ON text and indicator on the display. A simple thermostat Automations use the output of a sensor or other input condition, such as the time of day, to trigger an action. We will create a simple air conditioner thermostat that switches on the relay/LED when the temperature rises above 28°C and off again when the temperature falls below 27°C. These settings are convenient for testing with a finger on the temperature sensor. To implement the thermostat, the temperature reading is connected to the Relay/LED using two automations. On the HomeAssistant screen, go to Settings then Automations & scenes. Click on + CREATE AUTOMATION at the bottom right corner of the screen and Select “Create new automation” from the pop-up menu. Under “When”, click on + ADD TRIGGER. Select Device and choose “myHome” from the drop-down list. Select “myHome temperature changes” from the Trigger dropdown. Enter 28 into the Above field. The Below and Duration fields should be left blank. Under “Then do”, click ADD ACTION. Select Device and “myHome” as before. The Action is “Turn on myHome Relay LED”. Save the automation as “AC On”. Click the back arrow at the top of the screen to return to the “Automations” menu and create a second automation to turn the AC off. Under “When”, click on + ADD TRIGGER. Select Device and then myHome from the drop-down list. Select “myHome temperature changes” from the Trigger dropdown. Enter “27” into the Below field. Under “Then do”, click ADD ACTION. Select the Device myHome as before. The Action is “Turn off myHome Relay LED”. Save the automation as “AC Off”. The two automations will automatically activate within a minute. Go back to the Overview dashboard and hold a finger to the temperature sensor. The LED should light once the temperature rises above 28°C. The indicator on the dashboard should change, the relay LED should light, and the OLED display should indicate that the virtual AC is on. siliconchip.com.au When the temperature is allowed to fall, the relay LED should switch off below 27°C. Go back to the Automations & scenes menu and select “AC off”. Click on TRACES at the top right corner. The Trace Timeline tab should produce a screen very much like Screen 5; this view is useful when debugging more complex automations. We’ll have a follow-up article next month that describes how to use IR remote control to switch a split-system air conditioner on and off, a more realistic control method. Analog outputs We can set up GP16 to generate a 64kHz PWM signal that is smoothed by a simple RC filter and presented at CON6. The result is a voltage that’s proportional to the temperature, with the output scaled to a maximum of 3.3V at 33°C. The “monochromatic light” platform component is used as it provides a straightforward conversion from an input value to a brightness output. However, the conversion isn’t linear by default; the gamma value must be explicitly set to 1. Edit the configuration file’s “sensor:” block to add the on_value clause immediately after the “id: temperature” statement, then add a new “output:” block for the PWM at the end of sensor clause: ## PWM_temp.yaml ## PWM set by temperature ## Replaces existing temperature ## and humidity sensor code ## sensor: - platform: sht4x update_interval: 10s humidity: name: “Humidity” id: humidity temperature: name: “Temperature” id: temperature on_value: then: - light.turn_on: id: pwm_lamp ## 10 degrees/volt brightness: !lambda “return x/33;” Australia's electronics magazine September 2025  59 Screen 6: the myHome dashboard card with the PIR sensor. Also add the following after the sensor block: ## PWM_output.yaml output: - platform: rp2040_pwm pin: 16 id: PWM_16 frequency: 64000Hz light: - platform: monochromatic output: PWM_16 ## straight line temp:pwm gamma_correct: 1.0 name: “PWM lamp” id: pwm_lamp When the code is installed, the PWM output voltage at CON6 will track the measured temperature. PIR motion detection Connect a PIR sensor to the GP15 input at pin 1 on CON4, with 5V power and ground to CON1 and CON2, respectively. The required connections are shown in Fig.3. The sensor produces a binary value, so the code sits in a separate block to sensors that produce numeric values. Add the following code to your device in ESPHome Builder after the “sensor:” block, then save and install the changed configuration: ## PIR.yaml binary_sensor: - platform: gpio pin: 15 name: “PIR” device_class: motion id: PIR The MyHome card on the Overview dashboard should SC now look something like Screen 6. Fig.3: wiring for the PIR sensor is simple. In this example, Vout goes to GPIO GP15 (pin 1 on CON4), while 5V power comes from any combination of pins on CON1 & CON2. 60 Silicon Chip Australia's electronics magazine siliconchip.com.au