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When I was a kid, the general rule my mother told us was "You have to come home as soon as it gets dark". Well, in theory, that was great, but my mother wasn't always by a window, so "when it got dark" actually turned into "when mom noticed it got dark". With kids of my own on the way, I wanted to add my own geeky spin to that concept so I would always know "when it got dark" so that I could call out to the kids and tell them to come inside. In this Instructable, we'll create a project that can sense when it is dark outside and send us an alert text to go corral up the kids. We've automated Mom!

Step 1: Supplies

For this project, the Arduino Grove Starter Kit, will come in handy. It comes with the Arduino Base shield (which, just our lucky, fits the LinkIT ONE perfectly!) and the photocell sensor.

If you don't have the kit, don't fret. Hooking up a photocell sensor to a regular old circuit with a breadboard and jumper wires isn't that hard.

  • LinkIT ONE Board
  • prepaid SIM Card
  • Grove Arduino Base Shield
  • Grove Light Sensor (photocell)

Step 2: Configure Your LinkIT ONE Board

we dive in, it's good to get all our knobs and switches set to the correct setting. Make sure your board is set to the proper settings, as seen in the diagram above.

The most important one to consider here is that the SD/SPI switch needs to be set to SPI. This tells your LinkIT ONE to use the SIM card slot instead of the SD card slot.

Step 3: Insert Your SIM Card

Next, let's go ahead and get out LinkIT Board ready for text message sending! The most important aspect of that of course is a SIM card. If you don't have a spare sim card laying around, feel free to grab one out of your current phone (or a friend's) to borrow for prototyping real quick. You can always pop it right back in.

The card slides in pretty easily. Make sure you slide it in the direction of the arrow above (and not into the SD card slot, which is far too small). Then, attach the GSM antenna as picture to ensure you get a cell signal.

Step 4: Attach Grove Board and Light Sensor

Lucky for us, the Arduino Grove Base Shield fits right on top of the LinkIT ONE. This allows us to re-use the same base shield from our Arduino projects. Carefully align the pins to sync up with the arduino and press down. Sometimes this can take a bit of force, so it's OK if you get some resistance.

Once in place, we will want to hook up our photocell to act as our light sensor. Attach the Grove Photocell to the A0 slot, as it takes an Analog signal. This allows us to interact and get data from it.

Step 5: Deploy Code

The code for this project is simple enough: If we detect a certain threshold of light,send a text message that it is dusk and time to remind the kids to come inside.

I've also added in some simple bool variables to check for morning to give us a bit more accuracy. Hopefully the code is self-explanatory given how simple it is.

Download the attached .ino file and deploy it from your Arduino IDE to your LinkIT ONE.

Step 6: Deployment

Tape your LinkIT ONE board and photocell up near a window so it can get proper light.This way it will be able to tell if it is day or night. You might have to fidget with the photocell's light settings (within the code) in order to tell exactly what 'Dusk' is. Other than that, you should be ready to go!

Hopefully this instructable will get your kids home on time and safe before dark!

<p>That is a brilliant idea. Does it ever get false positives when it is just cloudy?</p>

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