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Honeywell HR25

This page describes the HW differences between the Honeywell (Rondostat) HR20 and the HR25 in an effort to get the OpenHR code running on the HR25. See http://embdev.net/topic/118781#new

  HR20 HR25
 MCUATmega 169V ATmega329PA
 Connected LCD 3xN segment
 4xN segment

This gives double the Flash, EEPROM & RAM (32Kbyte, 1kbyte, 2Kbyte respectively). As far as I can see there are no other differences.


The 10 pin connector pinout is identical to the HR20. A cheap ebay USB jtag programmer (that works with the 169 on the HR20) is, as it comes, unable to program this, even although it can read fuses and erase the flash. Update: the JTAG software can be changed and made to JTAG program the HR25s.

To get around this, I soldered on an ISP connector and used a cheap USBtinyISP programmer to get the code on.


Here are the pictures on the PCB. COM3 is now connected to the LCD, complete with cap to ground.



See the patch for the layout of the segments in code


Update: code now in svn. I've changed lcd.c/.h to cope with the new LCD layout, and also the Makefile to make a target for the hr25. Compile with make hr25. The resulting hex file will be hr25.hex.

There are no other changes in just now. The new parts of the LCD are currently unused.

User manual (in German)

JTAG connections

Pictures to aid my memory. Correct pinouts can be obtained from forum links. JTAG: Orange=PIN1 (TCK), Blue=PIN2 (GND).

(Unit pictured is an HR20, not HR25)


HR25 original firmware prints things at 9600 like:
>HR25 SW Version  109 from 31. May. 2011 12:00  HW Version 2
K: 0b10
>K: 0b0

It has its fuses set which stop reading of the code. There is a delay before the SW comes up - 1s+. Could this be a bootloader?

Zzz Zed,
14 Nov 2011, 14:15