This respository contains the firmware for the STM8S207 microcontroller on the Brew hardware PCB. Its purpose is to automate a 3-vessel HERMS Brew-system. Such a brew-system contains a Hot Liquid Tun (HLT), a Mash-Lauter Tun (MLT) and a boil-kettle (BK). There are also two pumps, eight valves, four flow-sensors and several temperature-sensors present. For heating there are both gas-burners and 3-phase electrical heating-elements present.
The current PCB and firmware have the following features:
- Reading of 6 x temperature sensors: two in the HLT (one I2C LM92, one One-Wire DS18B20), one in the MLT (I2C), one in the boil-kettle (One-Wire), one at the output of the counterflow-chiller (One-Wire) and one at the MLT return-manifold (One-Wire).
- Reading of one hardware temperature by a LM35 temperature sensor: this is used to protect the Solid State Relays (SSR) from overheating. The LM35 is typically mounted to a heatsink of one of the SSRs that switch a heating-element.
- Reading a maximum of 4 x FS300A flowsensors: between HLT and MLT, between MLT and boil-kettle, one at the output of the counterflow-chiller and one at the entry of the MLT return-manifold.
- Control of 8 x solenoid ball-valves at 24 V DC.
- 2 x PWM signals (25 kHz, 28 V DC) for the modulating gasburners (HLT and boil-kettle burners).
- Control of 4 x SSR outputs at 230 V AC: the pump, a second pump (for the HLT counterflow-chiller), 230 V enable for the HLT gasburner and 230 V enable for the boil-kettle gasburner.
- Control of 6 x SSR outputs at 230 V AC for the three phase heating-elements in the HLT and the boil-kettle. With this, heating of the HLT is possible with a gas-burner, with 1, 2 or 3 heating-elements of with any combination of these.
- Synced SSR outputs for HLT and boil-kettle, so that you only need one three-phase connection. The boil-kettle outputs have priority over the HLT outputs, meaning that if (on any phase of 230 V) both HLT and boil-kettle are heating, only the boil-kettle is activated. It is also possible to use just one (or two) of the three-phases, depending on the number of heating-elements inside the HLT and/or boil-kettle. The firmware is capable of addressing one, two or three heating-elements per kettle.
- Ethernet and USB connection to PC: USB-connection is used for debugging, main connection between PC-program and the firmware is Ethernet.
- Frontpanel LEDs (24 in total) that show the status of all actuators. They are controlled by a MAX7219 LED Display Driver, located on a separate PCB, the frontpanel PCB.
Block-diagram of the hardware
Abbreviations used:
- BK: Boil-kettle, one of the three brewing kettles in a HERMS configuration. Contains the wort that needs to be boiled.
- HLT: Hot Liquid Tun, one of the three brewing kettles in a HERMS configuration. Contains fresh water of a certain temperature.
- MLT: Mash-Lauter Tun, one of the three brewing kettles in a HERMS configuration. Contains the wort with the grains and typically has a filter inside to leave the grains inside the MLT.
- I2C: A digital interface between ICs, one of the most commonly used interfaces to connect ICs and sensors to a microcontroller.
- One-Wire: A digital interface between a sensor and a microcontroller, consisting of only one signal wire.
- PWM: Pulse Width Modulation, a signal representation that is used to control an actuator. It is a square-wave of which the duty-cycle is varied between 0 % and 100 %.
- SPI: a digital interface between ICs and a microcontroller. Together with the I2C interface, it is commonly found on a microcontroller.
- SSR: Solid State Relay, a device that switches 230 V AC and is controlled by a 5V signal from the microcontroller.
Integrated Circuits (IC) used:
- STM8S207R8: an 8-bits microntroller from STM-microelectronics running on 24 MHz and has 64 kB Flash onboard. If has 56 free GPIO pins available.
- TD62783: an 8-channel high-voltage Source Driver, they can switch up to 50 V and 500 mA per channel. Used here the switch the solenoid ball-valves.
- LM35: a precision centrigrade temperature sensor, delivering 10 mV per °C. The analog value is read in by one of the AD-converters of the STM8S207.
- LM92: a 12-bit + sign digital temperature sensor with I2C interface.
- DS18B20: an One-Wire 12-bit digital temperature sensor.
- DS2482: an I2C to One-Wire bridge, connects to a microcontroller via the I2C interface and controls a One-Wire device, such as the DS18B20.
- MAX7219: a LED display-driver IC, capable of addressing 8 7-segment displays or 64 individual LEDs. It has an SPI-interface. The MAX7219 controls the 24 Frontpanel LEDs of the brewing hardware.
- Wiz550IO: an auto configurable Ethernet controller that includes a W5500 (TCP/IP hardwired chip and PHY embedded), a transformer and RJ45 connector.
More hardware and firmware design details: see my website: http://www.vandelogt.nl/uk_hardware.php. Note that the description there is still for the old hardware version, based around an Arduino Nano.
Top view of v4.01 prototype PCB, as made by JLCPCB
Use with IAR-STM8.
The Brew-Hardware uses a network cable as its main-connection to the PC. This is powered through a WIZ550IO module. It uses DHCP to obtain an IP address automatically. The standard port number for the firmware is set to 8888.
The Brew-hardware also uses two virtual COM ports as a backup connection to the PC. Virtual COM port settings are (38400,N,8,1).
Typically the PC-program sends commands to the Brew-Hardware, like P0 (Pump Off) or P1 (Pump On). These commands are then executed by the firmware of the Brew-Hardware. Although you can type in the commands manually, it is more efficient to use a dedicated PC-program for it, with a Graphical User Interface.
If you install the Brew-Hardware PCB for the first time, it is best to use a terminal program that can handle a virtual COM port (I had good results with Realterm). At initial power-up, you can type S0 to retrieve the version number of the firmware (and to check that everything is working). The E1 command enables the Ethernet module, if everything goes well, the IP address of the Brew-Hardware is returned.
UART-communication at power-up
More information about the PC-Interface can be found at my website: http://www.vandelogt.nl/uk_hardware.php#PC_INTF