Using a ML8511 UV sensor and an Arduino Nano to test UV-filtering properties of sunglasses

Do cheap freebie sunglasses really block UV light or are they mostly just toys, which pose a serious health risk to your eyes? That’s the question I asked myself when coming across one of my wife’s cheesy glasses. I always warned her, but never could proof the potential risk of increased UV exposure caused by non-blocking tinted glasses. Until now…

After buying one of those cheap Arduino Nano clones (oh the irony), I started experimenting with all kind of sensors. One of them was the ML8511. This sensor detects 280 – 390 nm light most effectively. This wavelength is categorized as part of the UVB spectrum and most of the UVA spectrum. Overexposure to UVA radiation has been linked to the development of certain types of cataracts, and research suggests UVA rays may play a role in development of macular degeneration.

The setup was straight forward: I hung an UV LED torch over the sensor using my helping hand. The emitted 395 nm light is slightly out of range, but the torch has proven to be a reliable source of detectable UV light. Pointing the beam directly at the photo resistor was crucial as the amount of measurable UV light decreases rapidly on the beam’s edges. I used a sketch from Sparkfun to read the sensor’s output. The unit measure wasn’t really necessary as I was mainly interested in the relative amount of absorbed UV light. But having the Milliwatts per square Centimeter came in handy. The problem was that the script outputted -1 mW/cm² when being in an UV-free environment. The solution was unexpected: The voltage of the “supposed to be 1% accurate” 3v3 Nano output was in fact only 10% accurate and came out as being 3.61 volts. Seems like testing cheap sunglasses using even cheaper tools isn’t the best idea. However, the sketch’s output can be calibrated by adjusting the hard-coded reference variable in the script to the actual reference voltage.

All tested sunglasses absorbed a fair amount of UV light. The best pairs filtered the UV light nearly completely (meaning below a level that can be detected by an ML8511 in this particular setup and ignoring the minor UV halo around the frame due to the sensor not being fully covered by the glass). The rest ranged between letting 1 – 10% of UV irradiation to pass through – proving that all sunglasses had UV-filtering properties. Given that a good UV protection can be bought for less than 10 Euros (the best pair tested), it is probably a good idea to not use freebie sunglasses if you have a bad gut feeling. As general advice, make sure that you buy your glasses from trusted retailers (optician, pharmacy, supermarket, etc.) or let them be tested.

Seeing is believing. 😉

 

UV test setup with ML8511 and Arduino Nano R3
Serial monitor output of the sketch used

 

 /* 
 ML8511 UV Sensor Read Example
 By: Nathan Seidle
 SparkFun Electronics
 Date: January 15th, 2014
 License: This code is public domain but you buy me a beer if you use this and we meet someday (Beerware license).

 The ML8511 UV Sensor outputs an analog signal in relation to the amount of UV light it detects.

 Connect the following ML8511 breakout board to Arduino:
 3.3V = 3.3V
 OUT = A0
 GND = GND
 EN = 3.3V
 3.3V = A1
 These last two connections are a little different. Connect the EN pin on the breakout to 3.3V on the breakout.
 This will enable the output. Also connect the 3.3V pin of the breakout to Arduino pin 1.

 This example uses a neat trick. Analog to digital conversions rely completely on VCC. We assume
 this is 5V but if the board is powered from USB this may be as high as 5.25V or as low as 4.75V:
 http://en.wikipedia.org/wiki/USB#Power Because of this unknown window it makes the ADC fairly inaccurate
 in most cases. To fix this, we use the very accurate onboard 3.3V reference (accurate within 1%). So by doing an
 ADC on the 3.3V pin (A1) and then comparing this against the reading from the sensor we can extrapolate
 a true-to-life reading no matter what VIN is (as long as it's above 3.4V).

 Test your sensor by shining daylight or a UV LED: https://www.sparkfun.com/products/8662

 This sensor detects 280-390nm light most effectively. This is categorized as part of the UVB (burning rays)
 spectrum and most of the UVA (tanning rays) spectrum.

 There's lots of good UV radiation reading out there:
 http://www.ccohs.ca/oshanswers/phys_agents/ultravioletradiation.html
 https://www.iuva.org/uv-faqs

*/

//Hardware pin definitions
int UVOUT = A0; //Output from the sensor
int REF_3V3 = A1; //3.3V power on the Arduino board

void setup()
{
  Serial.begin(9600);

  pinMode(UVOUT, INPUT);
  pinMode(REF_3V3, INPUT);

  Serial.println("ML8511 example");
}

void loop()
{
  int uvLevel = averageAnalogRead(UVOUT);
  int refLevel = averageAnalogRead(REF_3V3);

  //Use the 3.3V power pin as a reference to get a very accurate output value from sensor
  float outputVoltage = 3.3 / refLevel * uvLevel;   // adjust outputVoltage to actual voltage in case you read negative values.

  float uvIntensity = mapfloat(outputVoltage, 0.99, 2.8, 0.0, 15.0); //Convert the voltage to a UV intensity level

  Serial.print("output: ");
  Serial.print(refLevel);

  Serial.print("ML8511 output: ");
  Serial.print(uvLevel);

  Serial.print(" / ML8511 voltage: ");
  Serial.print(outputVoltage);

  Serial.print(" / UV Intensity (mW/cm^2): ");
  Serial.print(uvIntensity);

  Serial.println();

  delay(100);
}

//Takes an average of readings on a given pin
//Returns the average
int averageAnalogRead(int pinToRead)
{
  byte numberOfReadings = 8;
  unsigned int runningValue = 0; 

  for(int x = 0 ; x < numberOfReadings ; x++)
    runningValue += analogRead(pinToRead);
  runningValue /= numberOfReadings;

  return(runningValue);  
}

//The Arduino Map function but for floats
//From: http://forum.arduino.cc/index.php?topic=3922.0
float mapfloat(float x, float in_min, float in_max, float out_min, float out_max)
{
  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;

}

 

Reference and further reading:

https://learn.sparkfun.com/tutorials/ml8511-uv-sensor-hookup-guide
https://en.wikipedia.org/wiki/Ultraviolet
http://www.canadianjournalofophthalmology.ca/article/S0008-4182(17)30495-7/fulltext

The straight forward way to backup all your phone’s files using the Android Debug Bridge

To copy all files from your Android phone’s internal storage to the current local dir using adb:

adb pull -p -a /sdcard/

(‘-p’ to display the transfer progress)
(‘-a’ means copy timestamp and mode)

 

The whole adb help for the sake of completeness:

Android Debug Bridge version 1.0.32
Revision eac51f2bb6a8-android

 -a                            - directs adb to listen on all interfaces for a connection
 -d                            - directs command to the only connected USB device
                                 returns an error if more than one USB device is present.
 -e                            - directs command to the only running emulator.
                                 returns an error if more than one emulator is running.
 -s <specific device>          - directs command to the device or emulator with the given
                                 serial number or qualifier. Overrides ANDROID_SERIAL
                                 environment variable.
 -p <product name or path>     - simple product name like 'sooner', or
                                 a relative/absolute path to a product
                                 out directory like 'out/target/product/sooner'.
                                 If -p is not specified, the ANDROID_PRODUCT_OUT
                                 environment variable is used, which must
                                 be an absolute path.
 -H                            - Name of adb server host (default: localhost)
 -P                            - Port of adb server (default: 5037)
 devices [-l]                  - list all connected devices
                                 ('-l' will also list device qualifiers)
 connect <host>[:<port>]       - connect to a device via TCP/IP
                                 Port 5555 is used by default if no port number is specified.
 disconnect [<host>[:<port>]]  - disconnect from a TCP/IP device.
                                 Port 5555 is used by default if no port number is specified.
                                 Using this command with no additional arguments
                                 will disconnect from all connected TCP/IP devices.

device commands:
  adb push [-p] <local> <remote>
                               - copy file/dir to device
                                 ('-p' to display the transfer progress)
  adb pull [-p] [-a] <remote> [<local>]
                               - copy file/dir from device
                                 ('-p' to display the transfer progress)
                                 ('-a' means copy timestamp and mode)
  adb sync [ <directory> ]     - copy host->device only if changed
                                 (-l means list but don't copy)
                                 (see 'adb help all')
  adb shell                    - run remote shell interactively
  adb shell <command>          - run remote shell command
  adb emu <command>            - run emulator console command
  adb logcat [ <filter-spec> ] - View device log
  adb forward --list           - list all forward socket connections.
                                 the format is a list of lines with the following format:
                                    <serial> " " <local> " " <remote> "\n"
  adb forward <local> <remote> - forward socket connections
                                 forward specs are one of: 
                                   tcp:<port>
                                   localabstract:<unix domain socket name>
                                   localreserved:<unix domain socket name>
                                   localfilesystem:<unix domain socket name>
                                   dev:<character device name>
                                   jdwp:<process pid> (remote only)
  adb forward --no-rebind <local> <remote>
                               - same as 'adb forward <local> <remote>' but fails
                                 if <local> is already forwarded
  adb forward --remove <local> - remove a specific forward socket connection
  adb forward --remove-all     - remove all forward socket connections
  adb reverse --list           - list all reverse socket connections from device
  adb reverse <remote> <local> - reverse socket connections
                                 reverse specs are one of:
                                   tcp:<port>
                                   localabstract:<unix domain socket name>
                                   localreserved:<unix domain socket name>
                                   localfilesystem:<unix domain socket name>
  adb reverse --norebind <remote> <local>
                               - same as 'adb reverse <remote> <local>' but fails
                                 if <remote> is already reversed.
  adb reverse --remove <remote>
                               - remove a specific reversed socket connection
  adb reverse --remove-all     - remove all reversed socket connections from device
  adb jdwp                     - list PIDs of processes hosting a JDWP transport
  adb install [-lrtsdg] <file>
                               - push this package file to the device and install it
                                 (-l: forward lock application)
                                 (-r: replace existing application)
                                 (-t: allow test packages)
                                 (-s: install application on sdcard)
                                 (-d: allow version code downgrade)
                                 (-g: grant all runtime permissions)
  adb install-multiple [-lrtsdpg] <file...>
                               - push this package file to the device and install it
                                 (-l: forward lock application)
                                 (-r: replace existing application)
                                 (-t: allow test packages)
                                 (-s: install application on sdcard)
                                 (-d: allow version code downgrade)
                                 (-p: partial application install)
                                 (-g: grant all runtime permissions)
  adb uninstall [-k] <package> - remove this app package from the device
                                 ('-k' means keep the data and cache directories)
  adb bugreport                - return all information from the device
                                 that should be included in a bug report.

  adb backup [-f <file>] [-apk|-noapk] [-obb|-noobb] [-shared|-noshared] [-all] [-system|-nosystem] [<packages...>]
                               - write an archive of the device's data to <file>.
                                 If no -f option is supplied then the data is written
                                 to "backup.ab" in the current directory.
                                 (-apk|-noapk enable/disable backup of the .apks themselves
                                    in the archive; the default is noapk.)
                                 (-obb|-noobb enable/disable backup of any installed apk expansion
                                    (aka .obb) files associated with each application; the default
                                    is noobb.)
                                 (-shared|-noshared enable/disable backup of the device's
                                    shared storage / SD card contents; the default is noshared.)
                                 (-all means to back up all installed applications)
                                 (-system|-nosystem toggles whether -all automatically includes
                                    system applications; the default is to include system apps)
                                 (<packages...> is the list of applications to be backed up.  If
                                    the -all or -shared flags are passed, then the package
                                    list is optional.  Applications explicitly given on the
                                    command line will be included even if -nosystem would
                                    ordinarily cause them to be omitted.)

  adb restore <file>           - restore device contents from the <file> backup archive

  adb disable-verity           - disable dm-verity checking on USERDEBUG builds
  adb enable-verity            - re-enable dm-verity checking on USERDEBUG builds
  adb keygen <file>            - generate adb public/private key. The private key is stored in <file>,
                                 and the public key is stored in <file>.pub. Any existing files
                                 are overwritten.
  adb help                     - show this help message
  adb version                  - show version num

scripting:
  adb wait-for-device          - block until device is online
  adb start-server             - ensure that there is a server running
  adb kill-server              - kill the server if it is running
  adb get-state                - prints: offline | bootloader | device
  adb get-serialno             - prints: <serial-number>
  adb get-devpath              - prints: <device-path>
  adb remount                  - remounts the /system, /vendor (if present) and /oem (if present) partitions on the device read-write
  adb reboot [bootloader|recovery]
                               - reboots the device, optionally into the bootloader or recovery program.
  adb reboot sideload          - reboots the device into the sideload mode in recovery program (adb root required).
  adb reboot sideload-auto-reboot
                               - reboots into the sideload mode, then reboots automatically after the sideload regardless of the result.
  adb reboot-bootloader        - reboots the device into the bootloader
  adb root                     - restarts the adbd daemon with root permissions
  adb unroot                   - restarts the adbd daemon without root permissions
  adb usb                      - restarts the adbd daemon listening on USB
  adb tcpip <port>             - restarts the adbd daemon listening on TCP on the specified port
networking:
  adb ppp <tty> [parameters]   - Run PPP over USB.
 Note: you should not automatically start a PPP connection.
 <tty> refers to the tty for PPP stream. Eg. dev:/dev/omap_csmi_tty1
 [parameters] - Eg. defaultroute debug dump local notty usepeerdns

adb sync notes: adb sync [ <directory> ]
  <localdir> can be interpreted in several ways:

  - If <directory> is not specified, /system, /vendor (if present), /oem (if present) and /data partitions will be updated.

  - If it is "system", "vendor", "oem" or "data", only the corresponding partition
    is updated.

environmental variables:
  ADB_TRACE                    - Print debug information. A comma separated list of the following values
                                 1 or all, adb, sockets, packets, rwx, usb, sync, sysdeps, transport, jdwp
  ANDROID_SERIAL               - The serial number to connect to. -s takes priority over this if given.
  ANDROID_LOG_TAGS             - When used with the logcat option, only these debug tags are printed.