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Connection variant 1

Advantage: Power is fed via Ethernet cable. Disadvantage: Occupies Ethernet cable.

[HR20] <--- Ethernet cable ---> [Converter module]

Converter module supplies both power and serial. If two HR20s should be controlled, then the same Ethernet cable can be used. Four wires per module suffice (Gnd, +3.3v, Tx (TTL), Rx (TTL) ).
Power(Gnd) - Rx: T568A/B White/Blue (4) -  Blue (5) cable pair
Power(+3.3) - TX: T568B White/Orange (1) - Orange (2) cable pair

Power(Gnd) - Rx: T568A/B White/Brown (7) -  Brown (8) cable pair
Power(+3.3) - TX: T568B White/Green (3) - Green (6) cable pair

Connection variant 2

Advantage: Power is fed via PoE Module. Can be routed further if a PoE Router is being used. HR20 with PoE PD module integrated

Connection variant 3

HR20 without PoE PD module. Power for the HR20 and Ethernet/wifi to RS232 converter is fed via a separate power supply.

Master/Slave connectivity

Each HR20 is per default connected to the master connecter. An additional slave output can be used to connect another slave.

Adapter cables convert RJ45 to DIP10. This requires a small module with multiple RJ45 connectors.


Using open HR20:
De facto standard firmware:
Latest source is now here
Antenna for 433/866MHz:
RF module:
HopeRF RFM12B 868Mhz Wireless Transceiver Module
Differences between RFM12 and RFM12B and functional description:
Connection between controller and RFM12B:
Bridging RS-232 to Wifi:
Bridging RS-232 to powerline:
Ebay: USR-TCP232-T-EN.pdf
openhr20 mit Ethernet-Controller ENC28J60 von Microchip:
Powerline adapter with firmware:
Programming Thermostat with AVRDRAGON in linux:
POE Power over Ethernet:
I've build a HM-11 Module into a "prototype" HR20-BTLE Version.

I just got around to programming the rest of my thermostats, and had to 
do the following:

sudo avrdude -p m169 -c dragon_jtag -e -B 12 -U flash:w:hr20.hex
sudo avrdude -p m169 -c dragon_jtag -U hfuse:w:0x99:m
sudo avrdude -p m169 -c dragon_jtag -e -B 12 -U flash:w:hr20.hex -U 
eeprom:w:hr20.eep -U hfuse:w:0x91:m

If I didn't flash the hex first, I was not able to set the fuse.
Security of HR20:

The best description I know of is in repository, 
(Compile with make hr25. The resulting hex file will be hr25.hex)

Android on virtualbox:

Bluetooth Gatt devices:
(enable communication with Bluetooth Smart or Smart Ready devices)   <--- mit Beispiel

Hersteller eurotronic:
App runterladen bei:
projects/electronics/openhr20.txt · Last modified: 2018/01/28 22:59 by admin