UV Meter

UV is important to reptiles (and people) in processing vitamin D3 which is needed to absorb calcium. Without it reptiles often suffer from Metabolic Bone Disease (MBD) which leads to weak bones and can be fatal.  Thankfully, pet shops have the answer, UV producing globes which can stave off the dreaded MBD.  These are in the form of T8 florescent tubes or compact florescent globes and go for $50+ each.  And, yeah, they need to be replaced periodically.    How do I know if I replacing a globe while it is still producing enough UV?  How do I know I haven’t waited too long?  The standard wisdom is to replace them every 6 to 12 months which can add up across multiple tanks not to mention the environmental impact of whatever goes in to making them.

Or, I can measure it.  UV meters sell for $400 but I thought I might be able to do something myself.

I had an Arduino Uno R3 and a TFT touchscreen lying around so I picked up a UV sensor and gave it a go.


The sensor

There are quite a few UV sensors around, most with a narrow frequency response.  While the wavelength of vitamin D3 absorption is around 300nm (UVB), UVA is also important for reptiles.  For this reason and to avoid missing the relatively narrow peaks in the output of commercial UV lamps I decided to go with the  ML8511 which seems to have the broadest wavelength band of the UV sensors I could find.  Reminder: Always read the datasheet, ideally before you buy it or you could be disappointed


ML8511 frequency response


Example UV lamp output (Exo Terra : Exo Terra CF lamp)

It produces an analog voltage relative to the UV intensity detected.  It is then easy enough to map the voltage to an intensity after sampling the analog voltage a few times to smooth it.  Some code was reused from a DFrobot example.

A quick walk outside and I could see the intensity to go from 0 to 3 mW/cm^2 which seemed reasonable for a mostly sunny winter’s morning in Melbourne.

Breakout for ML8511 from my usual go-to : ML8511 from core electronics


I used an Arduino UNO R3 clone and wired the sensor:

  • Power : 5V
  • Ground : Ground
  • Analog Output : A4 input.  (to avoid clashing with A0 to A3 which can be used by some of the display/keypad shields)

I soldered (well actually my friend did who has much steadier hands) it straight to the Arduino board to avoid the extra thickness of a prototype board.



Adafruit make these cool TFT resistive touchscreen shields for Arduino and I couldn’t resist buying one.  The screen update is pretty slow (visible flickering) when used with SPI bus but works really nicely in this project when I only redraw elements when they change.

The library provided with the screen and touch sensor work like a charm so integration was pretty straight forward.  It provides basic drawing functions like line, circle, rectangle and text but you need to build text box and button classes yourself if you want to simplify building a UI.

Adafruit TFT resistive touch screen available here.




The intensity varies (by the inverse square law) over distance so an intensity without a distance is not meaningful when judging to the output of the globe.  Instead of being forced to measure a distance each time I decided to measure the output right at the globe which involves sticking the device up and into each cage.  To avoid having to read off the screen while performing a yoga move I made the main output an output of the max output registered so I can put the device in the cage up to the globe and then pull it out to get a measurement.  I included a smaller instantaneous output and voltage output as well.  To reset the captured measurement I hit reset button on the screen.

The Max and Instantaneous values are displayed in a color indicating if they are in the range expected of a “good” globe.  Green for good, yellow for reduced and red for “its dead Jim”.

The tubes provide light across the length of the tube while the CFs provide a more concentrated source so the expected output for each is different at the globe.  To account for this the user can select CF or TUBE to change the assessment thresholds.

Finally, the zero mW/cm2 point seems to fluctuate a little (~0.02V) so I also include a calibration button which set the current instantaneous measurement to “0.0 mW/cm2”.



The Code

It is interesting writing Arduino code as it is C++ without the std template library (for memory reasons) so we have classes but no built in container classes for example.

It is a pretty simple application so I didn’t get too carried away.  I created a textbox class and then extended that to a button and provided just the visual customisation I needed (background colour, text colour & size, textbox size, textbox position).  I extended that for buttons with a simple isIn function for when the screen is touched and a selected flag to give it two states.

Check out the code here: UVMeter on GitHub

I update the display at 2Hz but only redraw objects that have changed, this avoids the flickering you get if you redraw objects each time.  Note, if a text value (i.e. a numerical display) is changing you need to redraw the background before rewriting the text as the text just redraws over the top leading to a mess of drawn pixels – hence a lot of text boxes with black background.

What is left

The device is not in a case yet and I currently power the Arduino with a mobile phone power pack.  I hope to build a case with a battery pack with 3D printing but it could take a while to get to the top of the list so if anymore is keen to do it let me know and I’m happy to be “first to be second” as they say.


This turned out to be pretty straight forward and useful.  Most of the time on the project will be in building a case for it!

Computer Vision – Egg hatching detection

The release of Raspberry PI 3 along with simple, low cost cameras makes entry in to camera motion detection simple and cheap.  For me this meant a handy (and cool) project to monitor my lizard egg incubator.

The Project

I have lizard eggs hatching a couple of times a week.  It is good to know when they hatch as I like to leave them in the incubator and then take them out after 24hrs.  Normally I check each day or two and then think, “did that just hatch or did it hatch just after I last checked?”.

I also wanted to trial the OpenCV image processing library as well as brush up on my Python.



I could try to train an algorithm to detect the various species of lizard in the image.  It could be done, and would be interesting, but a more straight forward approach is via motion detection.  The hatching process can take hours from start to finish so image to image at 24fps the changes will be very small, so how could it work?  Easy, take images every minute and compare it to a reference image; Use the difference between the images to judge what has happened.

Check out a timelapse video I created based on the images captured of a gecko hatching from it’s egg : Timelapse video

Part 1. Hardware

I used a Raspberry PI 3 to capture the images and do the processing.  It is perfect for the job : cheap, powerful enough for some processing, and has the libraries and ability to run python to make it all pretty easy.

The camera, I use a wide-angle IR camera with IR LEDs as it need to run day and night and ideally without visible light to disturb the day/night cycle of the lizards.  Make sure you get a wide-angle camera as the camera to object distance is small (~15cm)

Part 2. Image Capture

I won’t go in to detail about how enable the Raspberry PI Camera as there are plenty out there.  This is how I used it.  It can capture live images or run through a list of recorded files.  I record each image to allow for testing and training of the code.

Full code is available on GitHub : IncubatorMonitor code

 import picamera from picamera import PiCamera
 def go_replay(self):

    for f in self.files:
          (path, ext) = os.path.splitext(f)
          if (os.path.isfile(f) and ext == ".jpg"):
             img = self.process_image(f)
             print("reject", f, ext)
             # catch exceptions that might likely specific to 1 file.
       except (AttributeError, ValueError, TypeError, IndexError) as e:
       print("Caught", e, "while processing", f)


 def go_live(self):

    camera = PiCamera()
    high_res = (640, 480)
    camera.resolution = high_res

    while True:
       for i in range(1,10):
          filename = self.output_path + 'Incubator_'+ time.strftime('%m%d_%H%M%S')+ '.jpg'
          img = self.process_image(filename)

          print("Processed ", filename)

          #todo configure interval
          #split sleep to allow quicker interruption

       #write results periodically as it will probably end in tears (i.e. ctrl-C)
       print('Updated results')

Part 3. Basic Motion detection

This is where you go, “Oh, is that it?”.  It is much easier to write motion detection code in python.  The trick is detecting something useful and avoiding false-positives.

I use the Open Source computer vision library  OpenCV.  I’m barely scratching the surface of what can be done with it but if nothing else, it is a handy way to deal with images.

The hardest part is building OpenCV on the Raspberry Pi.  Here are instructions on how to do it.

Basic steps involved:

  1. Convert to grayscale.  Easier to deal with when only looking at a single intensity value per pixel.  Given the IR camera provides little real color detail we aren’t losing anything useful.
  2. Image difference.  Subtract one image from the other to detect differences.  The camera and the background is fixed so any change _should_ be interesting to us.
  3. Threshold the difference. There is some noise so the difference is never 0 for each pixel.  We use a threshold to detect changes of a meaningful level.  For this application a threshold of 15 to 20 is used.
  4. Dilate the thresholded data.  To smooth and merge (gross simplification) areas above the threshold perform a dilation step.  The size and content of the dilution matrix has an impact on how well this works.  I found a 9×9 matric with with MORPH_ELIPSE to work pretty well but could be improved on.
  5. Create polygons with each area above the threshold producing a list of objects to analyse.

Here is a snippet of the relevant code.  Again, full code is available here : IncubatorMonitor code

 se = cv2.getStructuringElement(cv2.MORPH_ELLIPSE, (9, 9))

 def __init__(self, blah):
 r = cv2.imread(self.path)
 self.raw = imutils.resize(r, width=500)
 blur = cv2.GaussianBlur(self.raw, (9,9), 0)
 self.processed = cv2.cvtColor(blur, cv2.COLOR_BGR2GRAY)

 def compareToReference(self, ref_obj, threshold):

    assert(len(self.processed) == len(ref_obj.processed))

    #compare to reference image
    self.delta = cv2.absdiff(self.processed, ref_obj.processed)
    # Check against threshold to find meaningful changes
    self.thresh = cv2.threshold(self.delta, threshold, 255, cv2.THRESH_BINARY)[1]

    # Run dilation to smooth and join nearby detections.
    self.dilate = cv2.dilate(self.thresh, self.se, iterations=4)

    #extract a list of separate detections.
    (_, self.contours, _) = cv2.findContours(self.dilate.copy(), cv2.RETR_EXTERNAL,
    self.output = self.raw

    # Create a box for each found movement.
    for c in self.contours:
       (x, y, w, h) = cv2.boundingRect(c)

       _ = cv2.rectangle(self.output, (x,y), (x+w, y+h), (0,200,0), 2)

    self.ref = ref_obj

From this we end up with a set of images showing the difference between the reference image and the image being analysed.

The Image:


  1. The raw difference between the image and reference.


2. The difference threshold


Dilation expands and merges the smaller detections.


Look, we found it!



Part 4. Image Classification

In a perfect world, we can just say each of these detections above the threshold are hatching events.  In practice, there are other things that can happen to trigger a difference between the images: removing the lid which has the camera on it, the light in the room going on and shining through the incubator window, moving the camera, moving the tubs inside, schrodinger’s lizard etc.

In this case the easiest thing to do for some of these is to control the environment:

  • Fix the camera to the inside of the incubator.
  • Cover the viewing ports on the incubator to avoid stray light.

To make things more interesting, I decided not to, to make the the software “smart” enough to tell the difference.

It needs to classify each image in to 1 of 4 categories

  • No detection
  • Found hatching
  • Detected temporary disruption
  • Environment changed, reset reference image.

This is a typical “classification” problem in machine learning terminology.

Start with something simple, some basic logic to separate these cases.  What features can we extract to judge between these categories?

  • No detection
    • Very little difference to the reference image
  • Found hatching
    • There is a noticeable change in 1 specific location.
  • Detected temporary disruption
    • There is a broad change between the image and the reference or a large number of localised differences.
  • Environment changed, reset reference image.
    • The images are very different.

So, how well does it work?

In short, pretty well.  It never misses a hatching and always detects a big reference change.  The problem, as to be expected, is false positives of hatching detection that should be classified as a temporary disruption.  This happens once or twice a week.

The solutions:

  1. Keep manually “tuning” (tinkering) the parameters to tune them out.  Probably would work but doesn’t address the underlying fragility.
  2. Put in some memory.  Temporary changes are temporary and hatching is forever so if we have an awareness of what has happened in the past then we can separate these 2 situations.  I’ve done this and it works but it offends me slightly.
  3. Use machine learning techniques to make a smarter assessment.  This sounds like more fun so it is what I will do next.  Logistic Regression or SVG? Neural Network?  We’ll see…

Part 5. Notification

For fun, I decided to tweet the notifications to my twitter account.  This is really straight-forward in python.  It can either send my a DM or post an update.

import tweepy
import json

class IncNotify():

def __init__(self):
# twitter_auth.json File Format
# "consumer_key" : "blah",
# "consumer_secret" : "blah",
# "access_token" : "blah",
# "access_secret" : "blah"

   twitter_auth = json.loads(open('twitter_auth.json').read())
   # Configure auth for twitter
   auth = tweepy.OAuthHandler(twitter_auth['consumer_key'], twitter_auth['consumer_secret'])
   auth.set_access_token(twitter_auth['access_token'], twitter_auth['access_secret'])

   self.api = tweepy.API(auth)

   ## TODO handle failure
   print ("Twitter output enabled")

def notify(self, img, level):

   # TODO img is correct format.
   if self.api is None or img is None or level == 0:
      return None

   msg = "The incubator monitor has detected a gecko hatching. Did I get it right?"

   if level <= 1:
      self.api.send_direct_message(user="namezmud", text=msg)
      path = img.output_path
      if not path:
         path = img.path
      self.api.update_with_media(path, msg)

   print("SEND!!!! " + img.getShortname())

Conclusion (so far)

There are still plenty of TODOs in the code and extensions that could be made but it works for now and I’ll set it up live for next breeding season.  Plenty to work on in what spare time I have.

If you are interested in giving it a go, feel free.  All the code is on github here for public consumption. IncubatorMonitor

The aftermath

Within the space of a week I had my PC stolen in a burglary and snapped in half the micro SD card in the raspberry PI.  These were where the images and backup for most of the hatching season were stored so I lost all my unit tests and most of my training data.  We’ll have to see if I have enough data left to train a machine learning model of if I have to wait until the end of the year to collect more data.  If there is anyone in the northern hemisphere breeding this summer and are interested in setting up a camera, please get in touch!