RootMaster

Note

This describes the revision 3 of the hardware. For the description of revision 2: RootMaster r2

Warning

The Raspberry Pi has been rotated 180° from revision 2. Please note the revision of your board before connecting the Raspberry Pi since it will be damaged if connected the wrong way!

Changes from revision 2

The major changes from revision 2 are:

• pH block changed to support external sensor hat. Either our own or EZO pH from Atlas Scientific

• Support for either BNC or SMA for pH probe

• Raspberry Pi rotated 180°

• Fixed known issues from Rev 2

Power

The RootMaster can be powered in two ways: via USB Power Delivery (USB-PD) or through a 12V barrel jack. The USB-PD input allows for flexible power options and can be used with a variety of USB-C power adapters. Please note that the USB-C power adapter must be 12 V capable. The 12 V barrel jack provides a more traditional power input method, suitable for use with standard 12 V power supplies.

STM32G473

At the core there is a STM32G473 that is connected to all external peripherals.

Hardware rev

The hardware revision can be read through 3 gpios. On rev 3 rev 0 should be read as 1 and rev 1 and rev 2 as 0.

Pin Number	Pin Name	Connected To	Note
8	PA0	HW rev 0	Should be read as 1
9	PA1	HW rev 1	Should be read as 0
10	PA2	HW rev 2	Should be read as 0

CAN-FD

There is a CANbus connecting the STM32 to Raspberry Pi and the external connection. This is CAN-FD compatible with a maximum speed of 1 Mbit/s. It is connected to the FDCAN3 peripheral in the MCU.

Pin Number	Pin Name	Connected To	Note
40	PB3	CAN-TX
41	PB4	CAN-RX

LEDs

RootMaster has two leds for status and debug. Both yellow.

Pin Number	Pin Name	Connected To	Note
2	PC13	LED1	Active Low
3	PC14	LED2	Active Low

Internal temperature and humidity sensor

There is an internal temperature and humidity sensor HDC1080 connected to I2C0.

Note: The i2c bus is also shared with the EC/temp sensor.

Pin Number	Pin Name	Connected To	Note
39	PA15	I2C0 SCL
44	PB7	I2C0 SDA

Temperature

The NTC temperature sensor is connected to the STM32G473 on pin 12 (PA4). This sensor is used to measure the temperature of the nutrient solution. The resistance of the NTC decreases as the temperature increases, and this change in resistance is measured by the ADC to determine the temperature.

The NTC temperature sensor is connected as part of a voltage divider circuit. The voltage divider is formed by the NTC thermistor and a fixed 49.9kΩ resistor. The output voltage of the divider, which varies with temperature, is fed into the ADC of the STM32G473 to measure the temperature.

Since the ADC of the STM32G473 cannot measure signals higher than 3.3V the signal is fed to a second stage dampening made up by another voltage divider consisting of a 18kΩ and a 33kΩ resistor. This scales the signal from 0-5V to 0-3.235V.

The resistance for the NTC thermistor can be calculated using the following formula given the ADC is 12 bit:

\[R_{NTC} = \frac {ADC_{VAL}*3.3V*R_1*(R_2+R_3)}{(5V*R_3*4095)−(ADC_{VAL}*3.3V*(R_2+R_3))}\]

If we replace the constants then the formula can be simplified to:

\[R_{NTC} = \frac {ADC_{VAL}*8396727}{675075000−(ADC_{VAL}*168300)}\]

Pin Number	Pin Name	Connected To	Note
12	PA4	NTC Temperature	Analog input

pH

The pH sensor interface must be used togheter with one of the sensor hats. This interface is connected to the i2c bus I2C1. Please see the respecive documentation for each on how to intefrate them into the software.

There is a GPIO on RootMaster that enables the pH peripheral that must be enabled before any readings can be performed.

Pin Number	Pin Name	Connected To	Note
14	PA6	pH disable	Active high, must be low to turn on sensor readings
30	PA8	I2C1 SDA
31	PA9	I2C1 SCL

EC and temperature

Pin Number	Pin Name	Connected To	Note
13	PA5	EC disable	Active high, must be low to turn on sensor readings
39	PA15	I2C0 SCL	Shared with temp/hum
44	PB7	I2C0 SDA	Shared with temp/hum

EC

The EC interface is using an ADS1115 ADC connected to I2C0. The 7 bit i2c address is 0x48. The EC value will be converted to a voltage on the AIN0 pin on the ADC. To work with as many probes as possible it is possible to set the gain using a MCP4017 digital potentiometer at the 7 bit address 0x2F. There is also a GPIO that enables the EC peripheral that must be enabled before any readings can be performed.

Temperature

There is a NTC interface connected to the same ADC as the EC on the AIN2 pin. The temperature NTC is connected as the bottom part of a voltage divider connected between 5 V and GND. The upper resistor is 49.9kΩ and must be taken into account when calculating the temperature.

Flow

The flow meter is connected to a GPIO pin and sends pulses proportional to the flow rate. Each pulse represents a fixed volume of liquid passing through the meter. The STM32G473 counts these pulses to measure the flow rate and total volume.

Pin Number	Pin Name	Connected To	Note
11	PA3	Flow meter	Pulse input

Digital in

There are 3 digital inputs that can be connected to various NC/NO sensors such as water level sensor or similar. All three inputs have pull ups connected to 3.3 V.

Pin Number	Pin Name	Connected To	Note
46	PB9	IN 1
43	PB6	IN 2
42	PB5	IN 3

12V high side switches

There are 6 high side switch outputs that can be used to connect valves or pumps. These outputs are capable of switching 0-12 V and are controlled using PWM signals from the STM32G473. Each switch can be individually controlled to regulate the power supplied to the connected devices.

Pin Number	Pin Name	Connected To	Note
29	PB15	Valve 1
28	PB14	Valve 2
27	PB13	Valve 3
15	PA7	Pump 1	TIM3 CH2
17	PB1	Pump 2	TIM3 CH4
25	PB11	Pump 3	TIM2 CH4

Raspberry Pi

The Raspberry Pi is used as the main controller for the RootMaster. To enable CAN on the Raspberry Pi, you need to modify the device tree overlay settings.

Enabling CAN

To enable the CANbus on the Raspberry Pi, follow these steps:

1. Open the boot configuration file:

   sudo nano /boot/firmware/config.txt
   

2. Add the file rootmaster.dtb to /boot/firmware/overlay

3. Open the systemd network configuration file:

   sudo nano /etc/systemd/network/80-can.network
   

4. Add the following:

   [Match]
   Name=can*
   
   [CAN]
   BitRate=1000000
   DataBitRate=1000000
   FDMode=yes
   

5. Save the file and exit the editor.

6. Reboot the Raspberry Pi to apply the changes:

   sudo reboot
   

1-Wire

To 1-Wire interface will be activated automatically by the rootmaster.dtb overlay

Verify that the 1-Wire devices are detected:

ls /sys/bus/w1/devices/

You should see a directory for each connected 1-Wire device.

Compatible peripherals

This is a list of peripherals that has been tested.

Peripheral	Link
Water pump 12V	AliExpress
EC + temperature	AliExpress