• Category Archives Arduino
  • Technology » Arduino
  • A possible new note taking application

    OneNote, FlashNote, Sticky Notes, Outlook notes and Ever Note are great applications However, if you have privacy concerns and or you are Blind and depend on assistive technologies, these applications probably don’t give you the usability, security and mobility that you need.

    If you are interested in this application, please Email me. If I don’t get enough interest, I won’t write it.

    A note taker should do the following:
    • Open really quickly and allow you to take a note right away.
    • Save automatically.
    • Securely and reliably upload to the cloud.
    • Allow you to retain ownership of your notes.
    • Give you a way of downloading your notes so that if you ever want to move to something new, you have a way of bringing your notes with you.

    The note taking application that I propose to create will provide the following features:
    • Encryption of all notes before they are uploaded by the client. Each note client will use a custom cert along with a custom password so that your notes can only be decrypted by you.
    • Hash tags. Tag your notes with keywords so that you can find notes that have words in common. For example, if you are referencing an upcoming holiday and you want to refer to your flights. Use the #Flights2016 tag so you can quickly jump to all mentions of that tag.
    • Notes will be in a tree structure. Create sub notes to group notes relating to a particular topic.
    • Search for any word contained in all notes.
    • Quickly create a note based on the current date and time.
    • Quickly minimise to the system tray.
    • Open links by pressing enter on the link or by clicking it.
    • Autocomplete using IntelliSense for hash tags.
    • Share a note by Email.
    • Download all notes as CSV.
    • For the next version: Create reminders based on a note.

    The cost of this application will be €15
    The initial version will work on Windows but I’d like to look at a cross platform client eventually.


  • Using date ranges in MongoDB and PHP.

    I have also written similar posts relating to date ranges in Python. You can find my Question here from when I was getting frustrated and The answer to my problems here.

    You seriously wouldn’t believe the trouble I’ve had in the past two weeks trying to make some progress on my Arduino, Raspberry pi, Python, PHP and MongoDB project.

    Work has been very busy so the only time I’ve had to work on this is on the bus on the way to and from Dublin and from time to time very late at night.

    Right, so here are a few of the problems I came up against:
    The first hing I wanted to do was limit the size of my table in MongoDB. I’m collecting quite a lot of sensor data from the Arduino but I don’t need to retain this data for any more than around 2 weeks.

    MongoDB allows you to create a TTL index which will delete data that was created more than a certain number of seconds ago. This is a really handy feature however, it didn’t really work for me. I think you need to store the date in BSON format and I had stored my date in ISO format because I think it will make it easier to retrieve and write the sensor entries.

    Regardless, here is the code I used:

    db.envirocheck.sensors.ensureIndex( { “Date”: 1 }, { expireAfterSeconds: 604800 } )

    You can learn more about TTL indexes using the Fantastic MongoDB documentation that covers TTL Indexes

    As I said, this didn’t work for me at all so a suggestion on Twitter that I received weeks before made me think of capped collections. These are similar to TTL indexes in that they delete old data but instead of the TTL index, this works by deleting entries that are old however it does so when the collection reaches a certain value. By writing data once a second, I find that with 500Bytes I can store just over two hours of data. I obviously need to figure out how many bytes I need for storing two weeks worth but that’s something to do when I’m feeling more awake.

    The code to create a capped collection is here:

    db.createCollection( “sensors”, { capped: true, size: 500000 } )

    Again, look here for the MongoDB documentation for capped collections.

    Next, I of course needed to set an index on my date field as I’m going to be using this to select specific temperature values for date and time ranges. That was quite straight forward.

    db.sensors.ensureIndex( { “Date”: 1 } )

    Next, I needed to find a way of selecting between two dates in MongoDB and PHP. You might think this is easy, but no! It’s far from it! I stupidly tried to get ahead of myself by making this really complicated. I looked at Doctrine but trust me on this, the documentation for this project is absolutely crap! Now, maybe it’s me. Maybe I’m not experienced enough to figure this out but for god sake, this documentation might seem great from a high level but unless you read it from start to finish like a book, it’s useless! there’s no context to any of their examples and huge chunks of code are missing without any pointers to the parts of the documentation that might reference them. I wasted a week reading that documentation. There’s also different variations and different versions so the whole thing is really frustrating. All I wanted to do was find data between a date or time range. I liked the simplicity of the query builder and I can really see the power of this library but the documentation really turned me off.

    Finally, I came to my senses last night at about 11:30PM when I really should have been a sleep. Come to think of it, I should really be a sleep now as well but I want to get all this out of my head and on paper so to speak before I forget it. I came across This post on the MongoDB blog which made things very very clear. I had of course tried something very similar to that before I started looking for alternatives but really, it was so simple! All I was missing was converting the date into strToTime before I tried to convert it into MongoDate format. I did a lot of searching on Google but although I could find shed lodes of documentation on converting from MongoDate into PHP, I couldn’t find anything on the other way around. I obviously wasn’t looking in the right place because as soon as I saw those few letters strToTime, it all clicked.

    Here’s the example from the MongoDB blog:

    $start = new MongoDate(strtotime(‘1971-01-01 00:00:00’));
    $end = new MongoDate(strtotime(‘1999-12-31 23:59:59’));
    $collection->find(array(“create_date” => array(‘$gt’ => $start, ‘$lte’ => $end)));

    This actually converts the date and time into a number like this:

    1393545599

    Armed with this information, I set about dynamically setting the date and time. This code will get the sensor values saved to MongoDB over the past day:

    $start = new MongoDate(strtotime(date(“Y-m-d H:i:s”,”-1 days”)));
    $end = new MongoDate(strtotime(date(“Y-m-d H:i:s”)));

    See how easy that is? Isn’t that frustrating! I’ve spent about ten hours reading about this. Such a waste in a lot of ways but I suppose I probably learned plenty on my travels to finding out more about Mongo and the way it handles dates. Funny, in the collection, the date is stored in ISO format. For example: 2014-27-02 23:46:05. It must do some very interesting conversion back into a standard format. When I tried to check using the format that the date is stored in within the collection using (Y-m-d H:m:s) it failed to pull back any records. Maybe because MongoDate is trying to parse that from the expected strToTime number. That’s weird though because that wasn’t even working when I wasn’t using MongoDate. It’s a question I must ask on the forums when I eventually get around to creating an account.

    As you can see, I’m still learning and in a lot of ways this is really frustrating. I could probably do with reading a few books on these subjects but where’s the fun in that? I rather learn as I go along.


  • Progressing slowly with the arduino and the Raspberry Pi

    Work on the Arduino and the Raspberry Pi is ongoing. So far, I’ve made Led’s flash, used a light meter to determine when the LED’s are on and off, taken the temperature of the room and moved a camera using a Servo. On the Pi side, I’ve set up Email alerts when motion has been detected by the phone and I even found an application that supports push on the IOS platform so I may even be able to get the Pi to send alerts directly to my iPhone.

    I’ve encountered a few challenges of course. Almost all of the tutorials for the Arduino use a delay function to pause when the servo is running or when the motor is spinning but that’s no good when you need the loop to continue processing while all of this happens. So, I looked into a few alternatives. Using a counter to count the milliseconds since the device was turned on was fine but this would need to reset after 34 days which would cause a problem with the timing of the loop. I then tried a library called ElapsedMilis. This works fine but I had a lot of problems figuring out the logic. I got there in the end though but unfortunately my approach wasn’t completely sound.

    After asking a question on the Arduino forum I was pointed in the direction of another library called Delay Timer. I don’t think it’s released because when I included it first in one of my projects I had a bit of debugging to do to get it working. I must subscribe to Git Hub to suggest my changes. Unlike my previous approach, with this library, I can use as many timers as I want. The last time, I was using one hardware timer and a number of intervals to try to mark when functions should be executed. This should have worked fine in theory but the problem is that the loop is processed so quickly that it can run through the process too quickly and miss an important event. With this new approach, I can have different timers running concurrently and I can check each one. When it is time to execute that function, the timer resets again and its place in the loop is never lost.

    Of course, it’s not all programming. Some of this work is also about putting the components together and making it sit properly. One problem I was having is that the servo was generating too much vibration. This would cause the camera to constantly think it was detecting motion. I came up with the great idea of using a bit of Velcro to help mount the servo to the side of the Raspberry Pi and then Velcro the camera board to the moving part of the servo. Now, the vibration is absorbed by the servo. It’s funny the solutions that show themselves when you’re stuck.