Archive for the ‘ Electronics ’ Category

A Little Bit of Future Plans

Since I still have some work to go to have my sensors and everything working fully, I thought I’d talk a little about some of my later plans, particularly automatic watering.

As I’ve said previously, my current greenhouse automation will turn the heater on when it gets too cold, but that’s it. Now that’s very useful and saves a lot of electricity over me having to go out there and turn it on and off when it needs to be done. To accomplish this, I have a power switch tail hooked up to my system that basically is a switch that switches 110 volts with only 3v. This is a pretty simple device to use, you plug one end into a socket (I use an extension cord), then plug the device into the other end. Next, you plug some wires from your micro controller (or in my case your micro computer) into the power and ground in the power switch tail.


Since I am able to control 110v devices with this device I can control a pump to move water from one place to another. So, my plan is to place a electric pump in a rain barrel and turn it on when the moisture level in the planters indicates that the soil is dry. I’ll hook the pump up to a drip system that will drip on all the trees.



This is the rain barrel and pump I plan on getting to accomplish this. I should be able to get both for maybe a little over $100. The one thing I kind of worry about is that the rain barrel only holds around 50 gallons and the pump will pump around 20 gallons per minute. I have to find out if there is a way I can tone it down a bit.


The other thing I have thought about is not wanting the pump to run when there is no water in the barrel. To do this I can use this float switch. When the water is below a certain level in the barrel I will set the code to not turn the pump on. I’ll have to drill a hole in the barrel to install it, but it should be easy to attach it to the ADC to determine if the switch is open or closed. I plan on running the program every 5 minutes to do all the logging and checking of the sensors.

Moisture Sensor Circuit

Tonight I thought I would post on how the rest of the moisture sensor circuit works since I think I have it going correctly now. I was using a transistor that was switched by a digital pin when it was time to run the program, but when I put it all together to test, it didn’t work at all. So this is what I have at the moment; which seems to work with the two sensors I have built right now. More testing will be required after everything is completed.


The first thing you’ll need is the rj45 female jack to plug your sensor into. Remember your order from previously as you’ll need to know which pins do what in your sensor.

When I created my sensors I used brown for into the moisture sensor, brown and white as out of the moisture sensor. Green was plus volts for the LDR and green and white is the ground side. The blue wire is the data wire; which leads us to the next step.


From looking at my plug and memory, I know that pin 3 should be data for the LDR. I run a wire from pin 3 to my analog input. (I use a raspberry pi so I have to have an ADC (analog to digital converter) to convert the analog signals from the sensor to something the pi can understand.


The next pin is pin 5 which is the brown wire or plus volts to the sensor. I connect this to a digital pin on my pi and in my code only set it to high (or power) when I need to so I don’t experience as much electrolysis. (I’ll show this in the code later.)


Next is pin 6 which is brown and white or the other side of the sensor. This also needs to be connected to an analog input

This should tell you how much moisture is in the soil by the amount of volts that transverse the sensor.


The next thing you’ll need to do is to put a pull down resistor on the yellow wire to ground. This is to pull the voltage reading down to zero when there is nothing going on with the sensor. I use a 10k ohm resistor for this



The last step is to connect pins 7 and 8 appropriately. Pin 7 is the green wire or power for the LDR (goes to +volts and pin 8 is the green and white wire ( aka ground for the LDR)

I still have a good amount of work to complete the automation system, but it seems to be coming along quite nicely.

Tomorrow I may show the code to
see how the relative moisture is captured or I may go to a different sensor (humidity, temperature, etc…)

Moisture Sensor

I recently decided that I needed to up my game when it came to my greenhouse automation, not because I’m lazy, but because I’m forgetful. My current system tracks the inside temp, outside temp and outside humidity and turns on a heater when it gets too cold. To accomplish this I use a raspberry pi with a ds18b20 temp sensor and a powerswitch tail 2.

Now I have since built some new planters for my citrus trees (will do a post on them later) and decided I needed to build a system that tells me when they need to be watered (and waters them, but that will come later as well). The first thing I needed to come up with was a moisture sensor to stick in the ground. This sensor measures both the relative moisture in the soil and the light the plant is receiving. This is what I eventually came up with:


If you’re interested in making one if these you’ll need some parts:


We need a 3″ piece of 1×2 cedar, a 3″ piece of 2″ craft board, some cat 5 cable, a rj45 jack, 10″ of 2×12 gauge electric wire, a LDR, a 10K ohm resistor, and some shrink tubing.

You’ll also need some tools and supplies:


These include a soldering iron and solder, a rj45 crimper and some wire strippers, hot glue gun and glue sticks, a staple gun, pliers and a lighter.



The first step is to place the jack on one end of the cat 5 cable. To do this strip back some of the wrapper and separate the wires. Place them in the order you would like (I used this order as I like the colors next to their white counterparts). Place the wires in the jack and put in the crimper and press it on. Cat 5 cables allow you to have 8 wires, but we only use 5.


The next step involves wiring up the LDR (light dependent resistor or light sensor). Strip of the wrapping on the other end (you’ll need a good amount) and separate the wires. I use the brown wire for plus volts into the moisture sensor, the brown and white wire for minus volts, the green wire for plus volts for the LDR, green and white for ground for the LDR and the blue wire for data on the LDR.

To wire the LDR you need to connect the green wire to one side (put your shrink tube over the wire before you connect them) the blue wire and one side of the 10k ohm resistor are connected to the other side of the LDR. The green and white wire is connected to the other side of the 10k ohm resistor. Once these are all connected solder them together to create a good solid connection.


Once they’re all soldered put some shrink tube over the ground side of the LDR connection.

Next, we need to put together our moisture sensor probes. Use your strippers again to pull the black and white wires out of the 2×12 gauge wire.


Once separated you will need to strip some off of each end of the wires. Just a little on the wire connection side and more on the side that will go into the ground.


After this solder the ends of the probes that will be in the dirt to prevent erosion.


Next, we need to connect the wires to the probes. Strip off a good bit from the cat 5 cables to make sure you can wrap it around the probe. Then solder the wires to the probes. (It helps to use a small vice to hold everything still while your soldering.


After we are all connected, we need to “mount” the probes to the wood blocks. I align them as shown in the picture, then staple the with 2 staples for each probe. I then go and use some pliers to push the staples in securely.


Almost finished!! Now we need to secure the LDR to the wood block. To do this I hold it down and use hot glue to secure it. I try to place the LDR a little above the top of the block. I also try to put some around all the other wires to make sure they don’t touch.



Finally, put the other piece of wood on top of everything and hot glue it together (this uses a lot of hot glue). I try not to cover the LDR with the glue but put it all around it.


For good measure I staple the cat 5 cable to the back of the block to move it back to the top of the sensor block.

This really does have most of the circuit for the LDR, but for the moisture sensor I use a transistor to cut the ground when I’m not using the sensor to cut down on electrolysis. In another post I’ll write about how I go about using this sensor.

If you have any questions just post in the comments. I have made 2 of these so far and still have 4 to go!!