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--- hr25_thermostat [2013/11/04 10:22] – add initial content (parts, wiring and links) GoHoHa
+++ hr25_thermostat [2013/11/06 20:14] – [Open the HR25 thermostat] typo corrected Inhumierer
@@ Line 1: / Line 1: @@
 ====== Modification of Honeywell HR25 thermostat  ======
-//to do//
+{{ :hr25.jpg?200|Figure 1: Honeywell Rondostat HR25 thermostat}}
+The Honeywell Rondostat HR25 is an electronically programmable thermostat for radiators.
+For integration into a smarthomatic network it needs a RFM12B transmitter and a new firmware.
+To keep the programming scheme similar to other smarthomatic devices, an ISP connector is added for easy flashing.
+The housing is hacker friendly, it opens without the risk of breaking it.
+The electronics is based on an ATmega329P processor.
+Initial idea is based on the development done for the HR20 thermostat, the OpenHR20 project.
 ===== Needed Parts =====
-You need a Honeywell Rondostat HR25 thermostat. It costs about 30,-EUR, but used items away for sometimes as low as 15,-EUR at [[http://www.ebay.de/sch/i.html?_nkw=Honeywell+HR25|ebay]]/[[http://www.amazon.de/gp/offer-listing/B0051UHFEI|amazon]] .
+You need a Honeywell Rondostat HR25 thermostat. It costs about 30,-EUR, but used items go away for sometimes as low as 15,-EUR at [[http://www.ebay.de/sch/i.html?_nkw=Honeywell+HR25|ebay]]/[[http://www.amazon.de/gp/offer-listing/B0051UHFEI|amazon]].
 ==== Partlist (in buildup order) ====
 ^  Amount  ^               Part              ^ Picture                         ^
-|    1     | Honeywell HR20/HR25 thermostat  | {{ parts: }}                    |
+|    1     | Honeywell HR20/HR25 thermostat  | {{ parts:hr25_small.jpg }}      |
 |    1     | Connector ISP 2x3 pin           | {{ parts:connector_isp.jpg }}   |
 |    1     | Transceiver PCB RFM12B          | {{ parts:ic_rfm12b.jpg }}       |
@@ Line 17: / Line 24: @@
 some thin short flexible wires to connect ISP and RFM12B with the PCB of the HR25 thermostat.
-===== Integrate it into a housing =====
+===== Hardware Modification =====
+==== Open the HR25 thermostat ====
+To open the housing, lift the turn wheel with a flat piece of plastic to avoid scratches.
+It snaps off and you can look into the device (Figure 2).
+Then remove the lock pins using the same plastic lever (see Figure 3, arrows to left and right).
+After pushing the 4 notches (see arrows in figure 5), the housing snaps open.
+Unscrew the PCB (just 1 screw) and slide it out.
+Sometimes the mounting contact is stuck on the housing.
+{{:hr25_removewheel.jpg?189|Figure 2}} {{:hr25_back_arrows.jpg?200|Figure 3}} {{:hr25_front_arrows.jpg?200|Figure 4}} {{:hr25_mainparts.jpg?216|Figure 5}}
+==== Integrate the additional electronics into the housing ====
+If a 2x3 PCB-pin connector is used for ISP, it is possible to hide it behind the turn wheel. This way it it easy accessible for reprogramming and there is little to no need to modify the housing or PCB((An other option would be to sacrifice the JTAG connector, cutting and wiring some connections.)).
 The RFM12B fits well inside the thermostat housing between display and PCB.
-If a 2x3 PCB-pin connector is used for ISP, it is possible to hide it behind the turn wheel. This way it it easy accessible for reprogramming and there is no need to modify the housing or PCB((An other option would be to sacrifice the JTAG connector, cutting and wiring some connections.)).
+{{:hr25_with_isp.jpg?200|Figure 6}}
 ==== Wiring of ISP and RFM12B ====
-//to do//
+The ISP (//tested, works//) and RFM12B (**not tested yet**) are connected as follows as shown on the right.
+You will need a fine solder tip. The best is to solder the wires to the back side (looking up to the display).
+{{:hr25_pinlayout_rfm12b_isp.png?300|Figure 7: Wiring of ISP and RFM12B to the Atmega329P}}
 ===== Flashing the firmware =====
@@ Line 37: / Line 66: @@
   * [[http://sourceforge.net/projects/openhr20/|OpenHR20 sourceforge project]]
   * [[http://www.mikrocontroller.net/articles/Heizungssteuerung_mit_Honeywell_HR20|Long thread about HR20 mods (GERMAN)]]
+  * [[http://embdev.net/topic/118781]]
   * [[https://piontecsmumble.wordpress.com/2013/02/25/openhr-20-tutorial-part-0-introduction|OpenHR 20 Tutorial]]
   * [[https://github.com/bruce33/openhr20|Bruce clone of OpenHR20 code with modification for HR25]]