We just bought a couple of cute looking plants for our new home. Between all the electronic gadgets filled in the house, the plants do bring a lively feeling. So in return, I wanted to do something for the plants.

That is why I built this smart planter. This device is extremely easy to make and is completely made out of recycled components. All you need to build this is a dead CFL bulb. Thankfully I keep the circuits before throwing those dead bulbs away.

So what does the smart planter do? Apart from giving the boring pots a cool futuristic look, the LED in the bottom indicates the amount of moisture content in the soil. The light becomes dimmer as the moisture content drops and completely turns off if the soil gets dry. Sounds cool? Lets make it!

Supplies

A dead CFL bulb ( contains transistor and resistor)

Power adapter (phone charger should do fine)

An LED

Step 1: Making the Base

Instead of modifying the whole pot, I just made a base on which the existing pot can sit. To make this base, I took an instant noodle cup (yeah I don’t throw them away) and cut the bottom portion. The plastic is very thin which makes it perfect to disperse light. I used a sand paper to make the edges smooth.

Luckily, the base I cut is almost exactly the same size as that of the bottom of my plant pot. In case yours isn't, It should be fine with any size. Or what you can do, is directly attach an LED strip to the bottom of you existing pot instead of making a separate base.

Step 2: Attaching an LED

For the light, you can simply de-solder one LED from the dead LED lamp. Unfortunately, none of the LEDs in mine worked. So, I used a blue LED from a broken RC car.

Generally LEDs are a little directional. They usually have the front made like a convex lens so that the light is focused to the front. We need the light to spread all around the base, so I first sanded the bulb of the LED with a sand paper for the light to disperse.

All you need to do is stick the LED under the base with some tape or superglue. Make sure to solder wires to the LED pins before that. It is a good idea to solder a 300 or 470ohm resistor in series to one of the LED pins in order to limit the current draw and prevent it from burning in case the power supply has a high voltage. If that is not available, it should be ok as long as you limit the supply voltage to around 3.3v to 5v.

I made a hole on one side of the base and passed the LED wires through it. The base is ready!

Step 3: Salvage the Components

Now lets have a look at the moisture sensor circuit so that we can decide which parts to salvage from the dead bulb. This is the most simple moisture sensor I could find on the internet (I have modified it a bit though).

As you can see you only need one transistor and two resistors. You can replace the variable resistor to any resistor between 1.5K to 20K. The 470 ohm resistor isn’t necessary. So just a transistor and a resistor. The NPN transistor is easy to find. There are usually two in a CFL circuit. While that would be perfect, I had a dead LED bulb which didn’t have one. So I salvaged it from the circuit of the same broken RC car.

For the resistor, you can easily find one in the bulb circuit, just look at the colour code to find its value. If you don’t know how to read the colour code, refer this link:

https://www.allaboutcircuits.com/tools/resistor-co...

Step 4: Make the Circuit

Once you have the components, you can solder them according to the circuit diagram. For the soil probes, I used a thin GI wire (Galvanized Iron wire) . You can use any wire or conductive material, but I used GI wire because it will not rust for a long time.

One downside of using recycled components is that the pins are generally small after de-solderig and soldering the circuit is a little harder. If you had the components with you already, then great! Once the circuit is ready, you can test it by inserting the probes to the soil. If the soil is moist, the LED should light up. If it doesn’t, and your connections are right, probably the transistor has a problem. Try replacing it with the other transistor in the bulb circuit.

I put the circuit inside a small tic tac container to prevent it from any water splashes.

Step 5: Illuminate!

Now all you need to do is insert the soil probes and place the pot on the base. You can make holes at the bottom of the pot to pass the probes to avoid hanging wires.

I used a 5v wall adapter to power the circuit. You can use a battery too. If your pot is outside, you can use a small solar cell to power it. The circuit doesn’t require much current. If I would have to make any changes, I would use an LED strip instead of a single LED which is a little dim in the day time.

All in all, this looks really beautiful, especially at night. You can build two such circuits from a single dead CFL bulb. So next time your room lights stop working, think twice before throwing them away.