Plant Watering Indicator (Part 1)

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If you are like me, you never think about watering your plants.  Well, you think about it but only when they look very bad because they didn’t had water for weeks…  🙂

I thought it would be fun to create a small prototype that would tell me when my plants need water.  Here it the final result:

 
 

The red LED flashed to indicate the battery is not dead.  The blue LED indicates that the plant needs water.  The longer it flashes, the more I should take a few seconds to water that plant!

I already had all the required components, including the Attiny13a and a soil humidity sensor.  If you don’t have one, simply search for “soil humidity sensor” on eBay and you will find many like this one:
humidity-sensor

 

The whole list:

  • 1X Attiny13A-SU
  • 2X SMT single row pin headers (2 pins)
  • 1X SMT single row pin headers (3 pins)
  • 1X SMT dual row pin headers (2X3 pins)
  • 2X SMT 0805 162 ohms resistors
  • 1 each SMT 0805 blue & red LEDs
  • 1X SMT 4.7uF electrolytic capacitor
  • 1X SMT 330NF ceramic capacitor
  • 1X Through hole single row header (2 pins)
  • 1X M1 SMT Diode (equivalent to 1N4001)
  • 1X soil moisture sensor kit (sensor + small board)
  • 4X AA batteries + casing
  • 1X Copper clad PCB
  • Optional: liquid tin

So, I started by thinking about what I wanted my project to do:
– Let me know that the batteries are not dead
– Try to use as little energy as possible, so batteries will last for a long time
– Give me an idea of the current humidity level instead of just warning me when I must water the plant

Having this in mind, I used Eagle to create the schematic of my project:
Capture d’écran 2015-11-15 à 16.54.07

I planned to use 4XAA batteries.  With the 1N4001 rectifier diode, I should never have more than 5.5volts, which is the maximum the Attiny can handle.  I wasn’t sure if the 2 LED would interfere with the ISP programmer, so I included jumpers to be able to disable the LED (in the end, it was useless).  Also, pay attention to the fact that the sensor is powered by an Attiny pin.  I was wondering if I should use a transistor to power on/off the sensor but I read that it takes less than 20mA, so it should be ok like that.  The schematic says the 2 resistors are 165 ohms, but it should read 162 ohms instead…

After that, I positioned the components on the board:
Capture d’écran 2015-11-15 à 16.55.04

I generated gcode for my ShapeOko 3 CNC, using Eagle, and milled the PCB.  If you are wondering, I am using a 0.5mm engraving bit (straight ones) to mill my boards, not the V-shape ones.  That way, I don’t have to care as much about how deep the tool goes in the PCB.  Once the CNC finished machining the PCB, I cleaned it with some acetone.  Then, I dipped it in liquid tin which is why the board finish is grey instead of looking like copper.  I do that to protect the copper.  It serves the same purpose as a solder mask, except that it is conductive.

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Then, I printed a layout of my board and added all the components on it.  I do that instead of trying to do PCB silk screen (have the component names written on the PCB).  Once I have all the components on that sheet, in the right orientation, I am ready to put the solder paste on the board.  I forgot to take a picture of that step, sorry about that.

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I added solder paste to the board, then I added all the components to the board and sent everything in my reflow oven.

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It was my 1st time using that reflow oven for real.  The solder paste I bought was supposed to melt at 137C degrees but I had to use a much higher temperature (200C) to obtain good results.  This is something I will have to look into, to figure out if the problem is with the soldering paste or with the oven.

Once the PCB was cold, I did a few tests and realized that I placed the M1 (equivalent to 1N4001 diode) and the red LED backwards.  I desoldered them using a hand soldering iron and placed them back properly.  It’s definitively not perfect but this is acceptable enough as a first prototype.

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The next step was to program the Attiny properly.  This is what I will share with you in Part 2 of this post!

 

One thought on “Plant Watering Indicator (Part 1)

  1. Pingback: Plant Watering Indicator (Part 2) | Francois' Corner

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