diff --git a/firmware/at.c b/firmware/at.c
index 81e6b00..c52891d 100644
--- a/firmware/at.c
+++ b/firmware/at.c
@@ -12,7 +12,7 @@
 #include "time.h"
 #include "led.h"
 
-#define PROJ_STR __PROJ_NAME " " __PROJ_REV " ::: " __PROJ_AUTHOR " " __PROJ_DATE
+#define PROJ_STR __PROJ_NAME  __PROJ_REV " ::: " __PROJ_AUTHOR  __PROJ_DATE
 
 #define UNUSED(X) (void)(X)
 
@@ -107,8 +107,8 @@ int8_t cmd_ati_handler(uint8_t mode, char* arg)
   if(mode != M_NORM) return -1;
 
   uart_puts_P(PSTR(PROJ_STR "\r\n"));
-  uart_puts_P(PSTR("compilation " __DATE__ " " __TIME__ "\n\r"));
-  uart_puts_P(PSTR("avr-libc v" __AVR_LIBC_VERSION_STRING__ " " __AVR_LIBC_DATE_STRING__ "\n\r"));
+  uart_puts_P(PSTR("compilation " __DATE__  __TIME__ "\n\r"));
+  uart_puts_P(PSTR("avr-libc v" __AVR_LIBC_VERSION_STRING__  __AVR_LIBC_DATE_STRING__ "\n\r"));
 
   return 0;
 }
@@ -182,6 +182,8 @@ int8_t cmd_at_dat_handler(uint8_t mode, char* arg)
   {
     case M_GET:      
       uart_puts(rtc_data->date_str);
+      uart_putc(' ');
+      uart_puts(rtc_data->weekday_str);
       uart_puts("\n\r");
       break;
     
diff --git a/firmware/rtc.c b/firmware/rtc.c
index f483d27..74e8a35 100644
--- a/firmware/rtc.c
+++ b/firmware/rtc.c
@@ -1,16 +1,20 @@
 #include <avr/interrupt.h>
+#include <avr/pgmspace.h>
 #include <avr/io.h>
-#include <stdlib.h>
 #include "rtc.h"
 #include "i2c.h"
 
 #define DEC_2_BCD(dec) ((((dec) / 10) << 4) | ((dec) % 10))
 #define BCD_2_DEC(bcd) (((((bcd) >> 4) & 0x0F) * 10) + ((bcd) & 0x0F))
 
+static const uint16_t days_of_month[] PROGMEM = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334 };
+static const char weekday_strings[] PROGMEM = { "mon" "\x00" "tue" "\x00" "wed" "\x00" "thu" "\x00" "fri" "\x00" "sat" "\x00" "sun" };
+
 static volatile struct RTC_DATA clock;
 static void (*rtc_handler)(struct RTC_DATA* clock);
 
 void rtc_read_datetime(struct RTC_DATA* data);
+uint8_t eval_weekday(struct DATE_YMD* date);
 
 void rtc_int0_init(void)
 {
@@ -35,7 +39,7 @@ void rtc_set_time(struct TIME_HMS* time)
 void rtc_set_date(struct DATE_YMD* date)
 {
   clock.buffer[3] = ((date->year & 0x03) << 6) | DEC_2_BCD(date->day);
-  clock.buffer[4] = DEC_2_BCD(date->month);  
+  clock.buffer[4] = (eval_weekday(date) << 5) | DEC_2_BCD(date->month);  
   i2c_writebuf(RTC_I2C_ADDR, 0x05, 2, &clock.buffer[3]);
   i2c_writebuf(RTC_I2C_ADDR, 0x10, 2, (uint8_t*) &date->year);
 }
@@ -122,5 +126,26 @@ void rtc_read_datetime(struct RTC_DATA* data)
   *(curr_char++) = (data->buffer[4] & 0x0F) + '0';
   *(curr_char++) = DATE_SEPARATOR;
   itoa(data->date.year, curr_char, 10);
-  *(curr_char+4) = 0;
+  *(curr_char+4) = 0;  
+
+  // data->weekday_str
+  strcpy_P(&data->weekday_str, weekday_strings + data->date.weekday * 4);
+}
+
+uint8_t eval_weekday(struct DATE_YMD* date)
+{
+  uint16_t yy = (date->year-1) % 100;
+  uint16_t c = (date->year-1) - yy;
+  uint16_t g = yy + yy/4;
+  
+  uint16_t jan1 = c / 10;
+  jan1 %= 4;
+  jan1 *= 5;
+  jan1 += g;
+  jan1 %= 7;
+
+  uint16_t day_of_year = pgm_read_word(&days_of_month[date->month-1]) + date->day;
+  if(!(date->year & 0x03) && date->month > 3) ++day_of_year;
+
+  return (jan1 + day_of_year - 1) % 7;
 }
\ No newline at end of file
diff --git a/firmware/rtc.h b/firmware/rtc.h
index b16c478..29146b3 100644
--- a/firmware/rtc.h
+++ b/firmware/rtc.h
@@ -24,6 +24,7 @@ struct RTC_DATA
   struct DATE_YMDW date;
   char time_str[9];
   char date_str[11];
+  char weekday_str[4];  
   uint8_t buffer[5];
 };