OpenHR20

This is a fork of OpenHR20 with RFM and Thermotronic support completely removed.

The goal of this fork is to provide a clean firmware with UART support for controlling the HR20 thermostats through external devices. Therefore RFM is obsolete and Thermotronic doesn't support UART, so support for both has been removed.

Why remove RFM support?

I am mainly interested in controlling my HR20's through an ESP8266 directly through the pin headers via UART. Since it will be powered through a DC adapter anyway, the increased power consumption doesn't matter as I won't be using batteries anyway.

Features

All original HR20/HR25 features
UART control through pin header
~~Wireless control through RFM radio module~~ (removed)

Planned

Migrate build to PlatformIO with MegaCore (as soon as ATmega169 support has been merged)
Guide for flashing
ESPHome module for integration with Home Assistant

Compiling

To compile the sources, avr compatible gcc crosscompiler is required. On many linux distributions, you can install this via packages, e.g. on debian based distros, installing "gcc-avr" package should install the whole required toolchain. For flashing, "avrdude" package is also required.

Prerequisites

Arch Linux based distributions

sudo pacman -Sy base-devel avr-gcc avr-binutils avr-libc cppcheck

Debian based distributions

sudo apt install build-essential gcc-avr binutils-avr avr-libc cppcheck

Compile the firmware

To compile the default configuration - HR20 version:

make

To compile with predefined REVision ID

make REV=-DREVISION="123456_XYZ"

To compile with hardware window open contact

make HW_WINDOW_DETECTION=1

OpenHR20 SW variants

*_sww - software window detection
*_hww - hardware window contact PE2<->GND (closed = connected, open=open)

Binaries

*.bin *.hex - flash on BIN and HEX format
*.eep - initial EEPROM content
*.elf - flash, eeprom and fuses combination
*.txt - info about compilation

Flashing

PINOUT HR20

The externally accesible connector on HR20/25 thermostats allows direct connection to the MCU for flashing via JTAG, or for wired communication. The connector layout is:

ATmega169PV	(<Port,Pin>/<No.>)
Vcc	RXD(PE0/02)	TDO(PF6/55)	TMS(PF5/56)	/RST(PG5/20)
GND	TDI(PF7/54)	TXD(PE1/03)	TCK(PF4/57)	(PE2/04)

Connection to JTAG

HR20	JTAG
Vcc	Vcc
GND	GND
RxD	-
TDI	TDI
TDO	TDO
TxD	-
TMS	TMS
TCK	TCK
/RST	NSRST
PE2	-

I used an AVR-JTAG-USB programmer from Olimex. AVR-JTAG-J (from Olimex), AVR DRAGON or AVR JTAG ICE (MKI & MKII) will work as well.

How to flash?

You can use the following commands to flash the firmware

# set your programmer:
#   jtag1 = AVR JTAG ICE MKI
#   jtag2 = AVR JTAG ICE MKII
#   dragon_jtag = AVR DRAGON in JTAG mode
#   or execute "avrdude -c ?" if you got another jtag programmer
export PROGRAMMER=jtag1

# the port of your programmer
export PORT=/dev/ttyUSB0

# the directory where backups will be stored (e.g. /your/current/directory/backups/2022-09-27_19:13:22)
export BACKUP_DIR=$(pwd)/backups/$(date "+%F_%T")

# backup fuse values
avrdude -p m169p -c $PROGRAMMER -P $PORT -U lfuse:r:${BACKUP_DIR}/lfuse.hex:h -U hfuse:r:${BACKUP_DIR}/hfuse.hex:h -U efuse:r:${BACKUP_DIR}/efuse.hex:h

# backup flash and eeprom (make sure to save these somewhere for the original firmware)
avrdude -p m169p -c $PROGRAMMER -P $PORT -U flash:r:${BACKUP_DIR}/hr20.hex:i -U eeprom:r:${BACKUP_DIR}/hr20.eep:i

# set fuses
avrdude -p m169p -c $PROGRAMMER -P $PORT -U hfuse:w:0x9B:m -U lfuse:w:0xE2:m

# change into the directory with the compiled firmware that you want to flash
cd bin/HR20_uart_sww

# write flash and eeprom
avrdude -p m169p -c $PROGRAMMER -P $PORT -e -B 12 -U flash:w:hr20.hex -U eeprom:w:hr20.eep

shawly / OpenHR20