diff --git a/Disconnected_CO2_Data_Logger/code.py b/Disconnected_CO2_Data_Logger/code.py
new file mode 100644
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+++ b/Disconnected_CO2_Data_Logger/code.py
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+# SPDX-FileCopyrightText: 2021 Liz Clark for Adafruit Industries
+#
+# SPDX-License-Identifier: MIT
+
+import time
+import board
+import digitalio
+import adafruit_scd4x
+import adafruit_sdcard
+import busio
+import storage
+import adafruit_pcf8523
+
+#  setup for I2C
+i2c = board.I2C()
+#  setup for SCD40
+scd4x = adafruit_scd4x.SCD4X(i2c)
+#  setup for RTC
+rtc = adafruit_pcf8523.PCF8523(i2c)
+#  start measuring co2 with SCD40
+scd4x.start_periodic_measurement()
+#  list of days to print to the text file on boot
+days = ("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday")
+
+# SPI SD_CS pin
+SD_CS = board.D10
+
+#  SPI setup for SD card
+spi = busio.SPI(board.SCK, board.MOSI, board.MISO)
+cs = digitalio.DigitalInOut(SD_CS)
+sdcard = adafruit_sdcard.SDCard(spi, cs)
+vfs = storage.VfsFat(sdcard)
+try:
+    storage.mount(vfs, "/sd")
+    print("sd card mounted")
+except ValueError:
+    print("no SD card")
+
+#  to update the RTC, change set_clock to True
+#  otherwise RTC will remain set
+#  it should only be needed after the initial set
+#  if you've removed the coincell battery
+set_clock = False
+
+if set_clock:
+    #                     year, mon, date, hour, min, sec, wday, yday, isdst
+    t = time.struct_time((2021,  10,   31,   00,  00,  00,    0,   -1,    -1))
+
+    print("Setting time to:", t)
+    rtc.datetime = t
+    print()
+
+#  variable to hold RTC datetime
+t = rtc.datetime
+
+time.sleep(1)
+
+#  initial write to the SD card on startup
+try:
+    with open("/sd/co2.txt", "a") as f:
+        #  writes the date
+        f.write('The date is {} {}/{}/{}\n'.format(days[t.tm_wday], t.tm_mday, t.tm_mon, t.tm_year))
+        #  writes the start time
+        f.write('Start time: {}:{}:{}\n'.format(t.tm_hour, t.tm_min, t.tm_sec))
+        #  headers for data, comma-delimited
+        f.write('CO2,Time\n')
+        #  debug statement for REPL
+        print("initial write to SD card complete, starting to log")
+except ValueError:
+    print("initial write to SD card failed - check card")
+
+while True:
+    try:
+        #  variable for RTC datetime
+        t = rtc.datetime
+        #  append SD card text file
+        with open("/sd/co2.txt", "a") as f:
+            #  read co2 data from SCD40
+            co2 = scd4x.CO2
+            #  write co2 data followed by the time, comma-delimited
+            f.write('{},{}:{}:{}\n'.format(co2, t.tm_hour, t.tm_min, t.tm_sec))
+            print("data written to sd card")
+        #  repeat every 30 seconds
+        time.sleep(30)
+    except ValueError:
+        print("data error - cannot write to SD card")
+        time.sleep(10)