diff --git a/avr/devices/0BUILD b/avr/devices/0BUILD
index be0570c..81d626e 100644
--- a/avr/devices/0BUILD
+++ b/avr/devices/0BUILD
@@ -33,10 +33,12 @@
     n25
     n26
     n27
+    n28
     r05
     r06
     s03
     t03
+    t04
   </subdirs>
 
 </gwbuild>
diff --git a/avr/devices/n28/.gitignore b/avr/devices/n28/.gitignore
new file mode 100644
index 0000000..8e0618c
--- /dev/null
+++ b/avr/devices/n28/.gitignore
@@ -0,0 +1,2 @@
+*.eep.hex
+*.obj
diff --git a/avr/devices/n28/0BUILD b/avr/devices/n28/0BUILD
new file mode 100644
index 0000000..a2d9bae
--- /dev/null
+++ b/avr/devices/n28/0BUILD
@@ -0,0 +1,21 @@
+<?xml?>
+
+<gwbuild>
+
+  <subdirs>
+    boot
+    main
+  </subdirs>
+
+  <extradist>
+    defs.asm
+    README
+  </extradist>
+
+  <data dist="true" install="$(datadir)/aqhome/devices/nodes">
+    aqua_n28.xml
+  </data>
+
+
+</gwbuild>
+
diff --git a/avr/devices/n28/README b/avr/devices/n28/README
new file mode 100644
index 0000000..c6733c4
--- /dev/null
+++ b/avr/devices/n28/README
@@ -0,0 +1,13 @@
+
+N28
+===
+
+- Role: Door sensor with temp sensor
+- MCU: AtTiny84
+- Connection: RJ45
+- Predecessor: N21, N16
+- Periphery:
+  - door sensor (TCRT1000)
+  - TWI interface
+    - SI7021 temperature and humidity sensor
+    
\ No newline at end of file
diff --git a/avr/devices/n28/aqua_n28.xml b/avr/devices/n28/aqua_n28.xml
new file mode 100644
index 0000000..700fa28
--- /dev/null
+++ b/avr/devices/n28/aqua_n28.xml
@@ -0,0 +1,17 @@
+
+<device name="aqua_n28" driver="nodes">
+  <manufacturer>AQUA</manufacturer>
+  <devicetype>N</devicetype>
+  <deviceversion>28</deviceversion>
+  
+  <values>
+    <value name="SI7021_TEMP"  id="0x01" type="sensor" dataType="rational" modality="temperature" units="C" denom="100" />
+    <value name="SI7021_HUM"   id="0x02" type="sensor" dataType="rational" modality="humidity"    units="%" denom="1" />
+    <value name="ADC"          id="0x03" type="sensor" dataType="uint16"                                    denom="1" />
+    <value name="MOTION"       id="0x07" type="sensor" dataType="rational" modality="motion"                denom="1" />
+    <value name="DOOR"         id="0x08" type="sensor" dataType="rational" modality="door"                  denom="1" />
+
+    <value name="LEDTIMING"    id="0x88" type="actor"  dataType="uint16" />
+  </values>
+
+</device>
diff --git a/avr/devices/n28/boot/0BUILD b/avr/devices/n28/boot/0BUILD
new file mode 100644
index 0000000..95d031c
--- /dev/null
+++ b/avr/devices/n28/boot/0BUILD
@@ -0,0 +1,32 @@
+<?xml?>
+
+<gwbuild>
+
+  <target type="AvrHexFile" name="n28_boot" >
+
+    <includes type="avrasm" >
+      -I $(builddir)
+      -I $(srcdir)
+      -I $(topsrcdir)/avr
+      -I $(topbuilddir)/avr
+    </includes>
+
+
+    <sources type="avrasm" >
+      boot.asm
+    </sources>
+
+
+  </target>
+
+
+  <subdirs>
+  </subdirs>
+
+  <extradist>
+  </extradist>
+  
+
+</gwbuild>
+
+
diff --git a/avr/devices/n28/boot/boot.asm b/avr/devices/n28/boot/boot.asm
new file mode 100644
index 0000000..cd8ec3e
--- /dev/null
+++ b/avr/devices/n28/boot/boot.asm
@@ -0,0 +1,129 @@
+; ***************************************************************************
+; Source file for base system node on AtTiny 84
+;
+; This is for the maintenance system (i.e. the flash loader).
+;
+; All definitions and changes should go into this file.
+; ***************************************************************************
+
+.equ clock=1000000 ; Define the clock frequency
+
+.nolist
+.include "include/tn84def.inc" ; Define device ATtiny84
+.list
+
+.include "version.asm"
+.include "../defs.asm"
+.include "devices/all/defs.asm"
+
+.include "common/calls.asm"
+.include "common/utils_io.asm"
+.include "common/utils_wait.asm"
+
+
+
+; ***************************************************************************
+; defines
+
+
+; ---------------------------------------------------------------------------
+; LED
+
+.equ LED_DDR             = DDRA
+.equ LED_PORT            = PORTA
+.equ LED_PIN             = PINA
+.equ LED_PINNUM          = PORTA3
+
+
+; ***************************************************************************
+; code segment
+
+.cseg
+.org 0x0000
+
+
+
+; ---------------------------------------------------------------------------
+; Reset and interrupt vectors
+;  rjmp start ; Reset vector
+  rjmp main ; Reset vector
+  reti ; EXT_INT0
+  reti ; PCI0
+  reti ; PCI1
+  reti ; WATCHDOG
+  reti ; ICP1
+  reti ; OC1A
+  reti ; OC1B
+  reti ; OVF1
+  reti ; OC0A
+  reti ; OC0B
+  reti ; OVF0
+  reti ; ACI
+  reti ; ADCC
+  reti ; ERDY
+  reti ; USI_STR
+  reti ; USI_OVF
+
+
+devInfoBlock:        ; 12 bytes
+devInfoManufacturer: .db 'A', 'Q', 'U', 'A'
+devInfoId:           .db DEVICEINFO_ID, 0
+devInfoVersion:      .db DEVICEINFO_VERSION, DEVICEINFO_REVISION             ; version, revision
+firmwareVersion:     .db FIRMWARE_VARIANT_BOOT, FIRMWARE_VERSION_MAJOR
+                     .db FIRMWARE_VERSION_MINOR, FIRMWARE_VERSION_PATCHLEVEL
+
+firmwareStart:   rjmp main ; will be overwritten when flashing
+
+
+
+; ***************************************************************************
+; main code
+
+
+.org BOOTLOADER_ADDR
+
+
+main:
+  rjmp bootLoader ; this routine is in modules/bootloader/main.asm
+
+
+
+
+; ***************************************************************************
+; includes
+
+.include "common/utils_wait_fixed.asm"
+.include "common/utils_copy_from_flash.asm"
+.include "common/utils_copy_sdram.asm"
+
+.include "modules/flash/defs.asm"
+.include "modules/flash/eeprom.asm"
+.include "modules/flash/io.asm"
+.include "modules/flash/io_com2w.asm"
+.include "modules/flash/flash1p.asm"
+.include "modules/flash/flashxp.asm"
+.include "modules/flash/flashprocess.asm"
+.include "modules/flash/wait.asm"
+.include "modules/bootloader/main.asm"
+.include "modules/network/msg/defs.asm"
+.include "modules/network/msg/crc.asm"
+
+
+systemSetSpeed:
+.if clock == 8000000
+  ldi r16, (1<<CLKPCE)
+  ldi r17, 0
+  out CLKPR, r16
+  out CLKPR, r17
+.endif
+
+.if clock == 1000000
+  ldi r16, (1<<CLKPCE)
+  ldi r17, (1<<CLKPS1) | (1<<CLKPS0)
+  out CLKPR, r16
+  out CLKPR, r17
+.endif
+  ret
+
+
+
diff --git a/avr/devices/n28/defs.asm b/avr/devices/n28/defs.asm
new file mode 100644
index 0000000..9d709d0
--- /dev/null
+++ b/avr/devices/n28/defs.asm
@@ -0,0 +1,131 @@
+; ***************************************************************************
+; copyright   : (C) 2025 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+
+; ***************************************************************************
+;
+;                                 AtTiny84
+;                                 --------
+;                            VCC  1     14  GND
+;                            PB0  2     13  PA0  TCRT1000_Enable
+;                            PB1  3     12  PA1  COM-DATA
+;                  /RESET    PB3  4     11  PA2  TCRT1000_Input
+;                            PB2  5     10  PA3  LED
+;                  COM_CLK   PA7  6      9  PA4  TWI-SCL
+;                  TWI-SDA   PA6  7      8  PA5
+;                                 --------
+;
+; ***************************************************************************
+
+
+
+.equ BOOTLOADER_ADDR = 0xd00
+
+.equ FIRMWARE_VARIANT_BOOT        = 0
+.equ FIRMWARE_VARIANT_TEMP_WINDOW = 1
+
+.equ DEVICEINFO_ID       = 'N'
+.equ DEVICEINFO_VERSION  = 28
+.equ DEVICEINFO_REVISION = 0
+
+
+
+; ---------------------------------------------------------------------------
+; LED module
+
+.equ LED_SIMPLE_ONTIME  = 1     ; shorter
+.equ LED_SIMPLE_OFFTIME = 50    ; longer
+.equ LED_SIMPLE_DDR     = DDRA
+.equ LED_SIMPLE_PORT    = PORTA
+.equ LED_SIMPLE_PORTIN  = PINA
+.equ LED_SIMPLE_PINNUM  = PORTA3
+
+
+
+; ---------------------------------------------------------------------------
+; LED activity module
+
+.equ LED_ACTIVITY_DDR     = DDRA
+.equ LED_ACTIVITY_PORT    = PORTA
+.equ LED_ACTIVITY_PORTIN  = PINA
+.equ LED_ACTIVITY_PINNUM  = PORTA3
+
+
+
+; ---------------------------------------------------------------------------
+; COM module
+
+.equ COM_BIT_LENGTH      = 52000 ; 104000ns=9600, 52000ns=19200, 26000ns=38400
+.equ COM_HALFBIT_LENGTH  = 26000 ; see https://de.wikipedia.org/wiki/Universal_Asynchronous_Receiver_Transmitter
+
+.equ COM_DATA_DDR       = DDRA
+.equ COM_DATA_INPUT     = PINA
+.equ COM_DATA_OUTPUT    = PORTA
+.equ COM_DATA_PIN       = PORTA1
+
+.equ COM_CLK_DDR       = DDRA
+.equ COM_CLK_INPUT     = PINA
+.equ COM_CLK_OUTPUT    = PORTA
+.equ COM_CLK_PIN       = PORTA7
+
+.equ COM_IRQ_ADDR_CLK   = PCMSK0
+.equ COM_IRQ_BIT_CLK    = PCINT7        ; bit 7 in PCMSK0
+.equ COM_IRQ_GIFR_CLK   = PCIF0
+.equ COM_IRQ_GIMSK_CLK  = PCIE0
+
+
+
+; ---------------------------------------------------------------------------
+; TWI master module
+
+;.equ TWI_BIT_LENGTH = 10000 ; 100000 and 200000 works for display: 10000, 100000, 200000
+.equ TWI_BIT_LENGTH = 1 ; 10, 100, 500, 100000 and 200000 works for display: 10000, 100000, 200000
+
+.equ TWI_DDR_SCL          = DDRA
+.equ TWI_PORT_SCL         = PORTA
+.equ TWI_PIN_SCL          = PINA
+.equ TWI_PINNUM_SCL       = PORTA4
+
+.equ TWI_DDR_SDA          = DDRA
+.equ TWI_PORT_SDA         = PORTA
+.equ TWI_PIN_SDA          = PINA
+.equ TWI_PINNUM_SDA       = PORTA6
+
+
+
+; ---------------------------------------------------------------------------
+; LCD module
+
+.equ LCD_TWI_ADDRESS      = 0x3c
+
+
+
+; ---------------------------------------------------------------------------
+; SI 7021
+
+.equ SI7021_ADDR          = 0x40
+
+
+
+; ---------------------------------------------------------------------------
+; ADC/TCRT1K
+
+
+.equ TCRT1K_LED_PORT    = PORTA
+.equ TCRT1K_LED_DDR     = DDRA
+.equ TCRT1K_LED_PIN     = PORTA0
+
+.equ TCRT1K_ADC_PORT    = PORTA ; adc2
+.equ TCRT1K_ADC_DDR     = DDRA
+.equ TCRT1K_ADC_PIN     = PORTA2
+.equ TCRT1K_ADC_MUX     = MUX2
+.equ TCRT1K_ADC_ADCSRB  = ADC2D
+
+
+
diff --git a/avr/devices/n28/main/0BUILD b/avr/devices/n28/main/0BUILD
new file mode 100644
index 0000000..cb38972
--- /dev/null
+++ b/avr/devices/n28/main/0BUILD
@@ -0,0 +1,34 @@
+<?xml?>
+
+<gwbuild>
+
+  <target type="AvrHexFile" name="n28_firmware" >
+
+    <includes type="avrasm" >
+      -I $(builddir)
+      -I $(srcdir)
+      -I $(topsrcdir)/avr
+      -I $(topbuilddir)/avr
+    </includes>
+
+
+    <sources type="avrasm" >
+      main.asm
+    </sources>
+
+
+  </target>
+
+
+
+  <subdirs>
+  </subdirs>
+
+  <extradist>
+    data.asm
+  </extradist>
+  
+
+</gwbuild>
+
+
diff --git a/avr/devices/n28/main/data.asm b/avr/devices/n28/main/data.asm
new file mode 100644
index 0000000..31ccc2f
--- /dev/null
+++ b/avr/devices/n28/main/data.asm
@@ -0,0 +1,14 @@
+; ***************************************************************************
+; copyright   : (C) 2025 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+
+
+.dseg
+
+
diff --git a/avr/devices/n28/main/main.asm b/avr/devices/n28/main/main.asm
new file mode 100644
index 0000000..39a6848
--- /dev/null
+++ b/avr/devices/n28/main/main.asm
@@ -0,0 +1,221 @@
+; ***************************************************************************
+; copyright   : (C) 2025 by Martin Preuss
+; email       : martin@libchipcard.de
+;
+; ***************************************************************************
+; * This file is part of the project "AqHome".                              *
+; * Please see toplevel file COPYING of that project for license details.   *
+; ***************************************************************************
+
+
+
+
+; ***************************************************************************
+; Source file for temperature sensor node on AtTiny 84
+;
+; This is for the full system (i.e. not the boot loader).
+;
+; All definitions and changes should go into this file.
+;
+;
+; ***************************************************************************
+
+
+.equ clock=1000000 ; Define the clock frequency
+;.equ clock=8000000 ; Define the clock frequency
+
+
+
+.nolist
+.include "include/tn84def.inc" ; Define device ATtiny84
+.list
+
+.include "version.asm"
+.include "../defs.asm"
+.include "./data.asm"
+
+.include "devices/all/defs.asm"
+.include "common/calls.asm"
+.include "common/utils_io.asm"
+.include "common/utils_wait.asm"
+
+
+
+; ***************************************************************************
+; defines
+
+; ---------------------------------------------------------------------------
+; generic
+
+.equ NET_BUFFERS_NUM            =  10
+.equ NET_MSGNUMINBUF_SIZE       =  8 ; max buffer nums in ringbuffer (global incoming)
+.equ NET_IFACE_OUTMSGBUF_SIZE   =  8 ; max buffer nums in ringbuffer (per interface outbound)
+
+
+
+
+; ---------------------------------------------------------------------------
+; firmware settings including list of modules used
+
+; #define MODULES_TIMER
+#define MODULES_CLOCK
+;#define MODULES_LED_SIMPLE
+#define MODULES_LED_ACTIVITY
+#define MODULES_NETWORK
+#define MODULES_COM2W
+#define MODULES_TWI_MASTER
+;#define MODULES_LCD
+;#define LCD_MINIMAL_FONT
+#define MODULES_SI7021
+;#define MODULES_STATS
+;#define MODULES_OWI_MASTER
+;#define MODULES_DS18B20
+;#define MODULES_MOTION
+#define MODULES_TCRT1000
+;#define MODULES_CCS811
+
+#define APPS_NETWORK
+;#define APPS_MOTION
+#define APPS_DOOR
+#define APPS_REPORTSENSORS
+#define APPS_STATS
+
+
+
+; ---------------------------------------------------------------------------
+; defines for values
+
+.equ VALUE_ID_SI7021_TEMP  = 0x01
+.equ VALUE_ID_SI7021_HUM   = 0x02
+
+.equ VALUE_ID_ADC          = 0x03
+;.equ VALUE_ID_REED1        = 0x04
+;.equ VALUE_ID_REED2        = 0x05
+;.equ VALUE_ID_DS18B20_TEMP = 0x06
+.equ VALUE_ID_MOTION       = 0x07
+.equ VALUE_ID_TCRT1K       = 0x08
+
+;.equ VALUE_ID_REED_CONF    = 0x81
+
+.equ VALUE_ID_LEDSIMPLE_TIMING = 0x88
+
+
+
+; ***************************************************************************
+; code segment
+
+.cseg
+.org 000000
+
+
+
+; ---------------------------------------------------------------------------
+; Reset and interrupt vectors (will be removed as soon as we can flash data over COM)
+
+;	rjmp main ; Reset vector
+        rjmp BOOTLOADER_ADDR ; Reset vector  ; use this for flashed system
+	reti ; EXT_INT0
+        rjmp com2wPcintIsr         ; PCI0
+	reti ; PCI1
+	reti ; WATCHDOG
+	reti ; ICP1
+	reti ; OC1A
+	reti ; OC1B
+	reti ; OVF1
+        rjmp baseTimerIrqOC0A ; OC0A
+	reti ; OC0B
+	reti ; OVF0
+	reti ; ACI
+        reti ; ADCC
+	reti ; ERDY
+	reti ; USI_STR
+	reti ; USI_OVF
+
+
+devInfoBlock:        ; 12 bytes
+devInfoManufacturer: .db 'A', 'Q', 'U', 'A'
+devInfoId:           .db DEVICEINFO_ID, 0
+devInfoVersion:      .db DEVICEINFO_VERSION, DEVICEINFO_REVISION             ; version, revision
+firmwareVersion:     .db FIRMWARE_VARIANT_TEMP_WINDOW, FIRMWARE_VERSION_MAJOR
+                     .db FIRMWARE_VERSION_MINOR, FIRMWARE_VERSION_PATCHLEVEL
+
+; ---------------------------------------------------------------------------
+; @routine firmwareStart @global
+
+firmwareStart:
+  rjmp main
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine onSystemStart
+
+onSystemStart:
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine onMessageReceived
+;
+; Called on every message received
+
+onMessageReceived:
+  clc
+  ret
+; @end
+
+
+
+; ---------------------------------------------------------------------------
+; @routine onEvery100ms
+;
+; Called every 100ms. Add your routine calls here. No arguments, no results.
+
+onEvery100ms:
+onEverySecond:
+onEveryHour:
+onEveryDay:
+  ret
+; @end
+
+
+
+onEveryMinute:
+;  lds r16, tcrt1kLastValue
+;  ldi r17, VALUE_ID_ADC
+;  ldi r22, AQHOME_VALUETYPE_UNKNOWN ; VALUE TYPE
+;  rcall Main_Send8BitValueReport
+  ret
+
+
+
+; ---------------------------------------------------------------------------
+; @routine onEveryLoop
+;
+; Called on every loop (i.e. after awakening from sleep).
+;
+onEveryLoop:
+  ret
+; @end
+
+
+
+
+
+; ***************************************************************************
+; includes
+
+.include "devices/all/hw_tn84.asm"
+.include "devices/all/includes.asm"
+
+
+
+; ---------------------------------------------------------------------------
+; defines for network interface
+
+.equ netInterfaceData = com2w_iface
+
+