Image courtesy of http://www.thepepperseed.com

They just look evil don’t they? If you’d like to purchase some, we bought our seeds online here: Carolina Reapers from Pucker Butt Pepper Co

It took a solid 30-40 days before our pepper seeds sprouted. It was probably a little colder than they would have liked, but four beans popped and so we promptly put them into our hydroponic system.

A fresh pepper sprout

The peppers will be grown using a 4-bucket undercurrent DWC system from Current Culture (Current Culture), along with the “I-Beam” 300W induction light from Brotherhood (I-Beam).

A picture of a pepper plant taken today

The Hydroid™ is handling all the feeding of the peppers. We’re using Current Culture’s new line of nutrients, and right now the Hydroid™ is filled with: Veg A/B, UC Roots, and pH Down from XNutrients (XNutrients).

After we filled the tanks with nutrients we hit the “Start” button and walked away. Our feeding targets were as follows:

Nutrient Concentration: 700µS (350ppm NaCl or 490ppm 442)

pH level: 6.2

Here’s a log of what happened:

Caveat — The EC is high starting out because we had to use tap water for this go-around. We’ll get a good RO system in here shortly.

A couple interesting things of which to take notice. First, the Hydroid™ hit its targets dead-on. Second, the resolution of the log is so good, and the dosing so predictable that you can actually identify the discrete nutrient injection events in the EC plot, and you can see a very pronounced stair-step pattern in the pH plot too. Everything is adjusted very slowly and predictably. It’s neat that we’re able to take something so dynamic and reduce it to something very stable.

We’ll keep posting updates as the peppers continue to grow, and we’ll impatiently wait for the harvest. Thanks for checking us out!

Jump To:
The Inverse Square Law
The Test Setup
The Results
Conclusion

The Hydroid has the unique ability of interfacing with external analog sensors. This is a really powerful feature that we wanted to highlight. And how better to illustrate the usefulness of this feature than a real-world example? But first, a quick word on PAR…

PAR, or photosynthetically active radiation, is a fancy way of saying, “a color of light the plants require to perform photosynthesis.” Not all light is created equal. The “color” of light depends on the frequency of the photons (light at the “quantum level”) hitting some sensor, like your eye. As the photon frequency increases, the color becomes more “blue”. As the frequency decreases, the color becomes more “red”. This frequency can be converted into a wavelength, which is what is typically used to express the color of light. PAR light is roughly between 400-700 nanometers. Just because a light looks bright doesn’t mean your plants can use it for photosynthesis!

What’s nice is, there are actually sensors tuned to respond to this very wavelength of light. In other words, this sensor can tell us how intense this particular range of light is. But how is this useful?

• Monitor your light’s PAR output as it ages to determine when it needs to be changed
• Optimize PAR intensity for your plants
• Measure light coverage with different reflector designs to identify dead spots
• Compare the PAR output between different bulb brands

So, there’s a tremendous amount of optimization you can accomplish just with a PAR sensor. Managing and making sense of the data can be difficult, but it’s actually pretty straightforward with the Hydroid. Let’s start with an easy example and use a PAR sensor to study the intensity of a particular light.

 

The Inverse Square Law

Theoretically, light intensity should decrease as you move away from the source. Of course it does! But how quickly does light intensity actually drop off as you move away from the source? And how far away can I move my light from my plants and still get reasonable intensity?

The change in light intensity as you move away from a point source isn’t actually linear as you might think it would be. Increasing the distance from a light source doesn’t just half the total light intensity, it’s actually reduced to a quarter of the original light intensity! This has tremendous implications, and is a function of how light propagates from it’s source.

Wikipedia, (2008), Inverse square law.svg [ONLINE]. Available at: http://en.wikipedia.org/wiki/Inverse-square_law [Accessed 20 February 13].

Light intensity versus distance follows what is called “The Inverse Square Law” which says:

The above equation states that light intensity is proportional to one over the distance squared. That means, every time you double the distance from the light, the intensity decreases by 75%. If you triple the distance from the light then the intensity decreases 89%. If you quadruple the distance from the light the intensity decreases 94%. If you were to graph the theoretical light intensity versus distance from the source it would look like the following:

Graph of theoretical light intensity versus distance.

We have another visualization of this concept below. The number “units” are inconsequential. You can think of these as “feet” or “inches” or whatever unit you’re comfortable with. The point is, if we take point “1” as the position of our light source, then if we double the distance (i.e. point 2) the light intensity will be reduced to one-quarter the original intensity. Point 3 would be one-ninth the intensity of the first point, and so on.

Visual representation of the inverse square law of light.

We can actually use the Hydroid and a good PAR sensor to measure our light intensity with respect to distance from a point source. With this we’ll be able to actually test the inverse square law and see how it holds up in practice.

The Test Setup

We had a T5HO fluorescent light hood taking up space at our facility so we decided to use that for our test. We used an inch-scale to measure from the bottom of our light. The idea here is to take a series of PAR measurements at increasing distances to see how PAR intensity changes. If the theory holds true (and we set up our test properly) then the light should be reduced by the square of the distance.

We used an Apogee SQ-225, pictured below, which is a 5-volt amplified PAR sensor. 

Apogee SQ-225 Amplified PAR Sensor.

The voltage from this sensor increases to 5 volts as the PAR intensity increases.

Since the Apogee SQ-225 is a 0-5v analog sensor we can plug it directly into the rear of the Hydroid labeled “Analog Input 2”. Once we open the Grohaus software we can navigate to the Settings page where we can specify which sensor we have plugged into Analog Input 2. Here I’m just selecting the Apogee SQ-225.

Plugging the Apogee PAR sensor into Hydroid Analog Input port.

Selecting the Apogee PAR sensor in the Grohaus Software.

Note: If you don’t see your sensor listed contact Grohaus Automation.

Now we can click on the analog input button to view the data coming from the Apogee PAR sensor.

Example PAR sensor readout expressed in Photosynthetic Photon Flux (PPF).

The above screenshot is an example of the output from the PAR sensor. The data is graphed in real-time, it includes a digital readout at the top-left of the screen, and on the bottom-right as well. The software expresses PAR in units of PPF, or “photosynthetic photon flux”. That’s basically a representation of how many photons hit a given area. In this case, it’s how many micro-moles of photons hit a square meter area, per second. Now that we’re reading from the sensor appropriately we can start collecting data.

Below is a report of the PAR readings we collected from our test. Again, all we did was measure PAR from a light source at increasing distances. If we graph this data it should look very similar to the theoretical plot discussed above.

The Results

Resulting PAR data.

Since the data has been entered into a spreadsheet program we can graph this data to see how it lines up with the theoretical inverse square law plot. Below I have the ideal inverse square law plot overlaid on top of the actual data we collected. If our test was 100% perfect, the graphs should line up exactly on top of each other.

Ideal (RED) and Actual PAR data (BLUE) overlaid.

Isn’t that nice? The shape of the curves are very close even if the points aren’t an exact match. There are a number of reasons why the points don’t line up with each other (mostly likely due to testing errors), but the important point here is that the curves are the same. This means that the Apogee sensor is correctly indicating that PAR intensity drops off with the square of the distance, as evidenced by the steep incline of the graph as we approach the light, and the asymptotic nature (i.e. the graph becomes nearly parallel with the horizontal axis) as we move further and further away from the source.

Conclusion

This illustrates two very important points: First, there is tremendous value in managing radiant heat emanating from your lights so you may bring them as close as possible to your plants. Why spend big bucks on a 1000W light when it’s so hot that you have to keep it several feet away from your plants? According to the data we collected, doing so means only a small fraction of the light from that expensive bulb is actually making it to the leaves. So it’s important to consider the trade-off between light intensity and heat, and a PAR sensor may be able to help you find the best position for your lights.

Second, this test proves our PAR sensor it outputting sensible data. With this we can do all sorts of things. If a salesman from bulb “Brand X” promises you the world with their bulb, now you can actually quantify how good their bulbs are compared to yours. Or, you can monitor the change in PAR over time to determine when it’s appropriate to replace your bulbs with new ones. The implications here are far-reaching.

The PAR sensor really is an invaluable tool that too few people utilize. Now that you can combine it with a Hydroid, which will allow you to easily monitor and log PAR data, there’s even less of a reason not to use one.

We breezed through the explanation of PAR and the inverse square law to prevent this blog from becoming too cumbersome, so if you’d like a more in-depth explanation of either concept and google is failing you, try these links:

PAR: http://www.sunmastergrowlamps.com/SunmLightandPlants.html
Inverse Square Law for Light: http://www.ifa.hawaii.edu/~barnes/ASTR110L_S03/inversesquare.html

For any questions or comments please contact Grohaus.

You can think of the Hydroid as performing two major functions in your garden: It feeds your plants as necessary, and it will intelligently control any devices that you use in your grow area. So everything you see here is designed to serve those two purposes. Let’s take a closer look at how the nutrient doser works first.

The heart of the Hydroid system is the enclosure containing the nutrient dosing equipment. It utilizes a pneumatic injection system, relying on compressed air to push nutrients into a hydroponic system. The system does not rely on gravity in order to deliver nutrients.

The 1-gallon nutrient containers you see inside are made from high density polyethylene. They were custom made for our product, which means they’re designed specifically for use with hydroponic solutions such as pH modifiers and concentrated nutrients. No need for dilution here.

You can also see the white and black solenoid valves scattered along the base of the system. These electronic valves control the flow of nutrients through the delivery lines. When the computer determines that your plants are hungry each solenoid valve opens for a period of time proportional to your specified nutrient ratio.
The gold colored item in the picture is the air compressor. This is used to maintain pressure within the nutrient containers. If the Hydroid didn’t use an air compressor the alternative would be gravity feeding, which requires placing potentially heavy fluid containers up in the air. Not only can this be dangerous, but it also doesn’t provide consistent flow through the nutrient lines as the water level drops. The tanks are maintained at 10psi during injection events, and a relief valve vents the pressure once the nutrient dosing is complete.

Also note the green circuit board hiding in the back of the Hydroid. This is the brain of the system, and this is also where the majority of devices are connected. More on this in a minute.

Finally, note the bulkhead connectors on the side wall of the Hydroid. All connectors utilize polypropylene seals which means they’re safe for whatever hydroponic chemicals you wish to use. The outlet of each solenoid goes to one of these bulkhead connectors, and ultimately ends up somewhere in your hydroponic system. We include 50 feet of tubing so there should be plenty of flexibility in running nutrient lines.

In the third picture we have the complete Hydroid system sitting in front of our drink dispenser. The drink dispenser uses the exact same hardware as the Hydroid nutrient doser, but instead of dispensing nutrients it dispenses mixed drinks! We brought it to the Maximum Yield Indoor Gardening Expo and thought it would be a cool way to demonstrate our injection system.

But here you can get a sense of scale for everything, and you can see everything that comes with the Hydroid. From left to right you have the SensorBox, which houses all of the atmospheric sensing equipment (more on that in a minute). Next to that you can see the 10″ touch-screen tablet computer. This what we recommend people use to interface with the Hydroid. The software is formatted for a 1024×600 resolution screen, and the touch interface is almost identical to interfacing with your favorite smart phone…no keyboard or mouse required.

It’s difficult to see in the picture, but next is the pH and EC probes. Both probes are laboratory grade, and because we use custom designed pH and EC circuits you’ll never pickup any unwanted RF interference from your digital ballasts. We went through great lengths to ensure that the sensing is impervious to RF noise.

Lastly we have the AuxBox. The AuxBox is what the Hydroid uses to turn devices on and off. You can think of it simply as a relay in a box. You plug your device into the Auxbox, the AuxBox power into the wall, and the RJ45 plug goes into the Hydroid. You can then program the Hydroid to turn your device on and off relative to whatever process you choose. Want your exhaust fans to turn off when your CO2 generator turns on? No problem. Want to turn on a dehumidifier when your relative humidity gets too high? Again, no sweat. These boxes are really powerful when used in conjunction with our control software as you can control nearly anything you want.

Let’s get back to the SensorBox for a moment. The SensorBox is used to sample the ambient conditions in your garden. It uses an infrared CO2 sensor to measure carbon dioxide concentration, and also samples the ambient temperature and humidity. The data cable we use is fine being run over long distances, so there’s a lot of flexibility as to where you can put it. Not to mention, it does have a small fan inside which helps move air over the sensors inside.

Lastly, we wanted to point out the hookups on the back of the Hydroid. Some of them are pretty self-explanatory, but a few of the connectors towards the bottom may need some detail.

Tank expansion is exactly as it sounds: If you need more tanks, you can hook up another five to the standard five that come with the Hydroid for a total of ten.

Below that you have some alarm inputs and outputs. So what are those good for? Alarm inputs can be used to connect devices that sense problems in your grow room. For instance, if you leave your space for long periods of time you can connect flood or smoke detectors. If there is a problem you can have the Hydroid send you a text or email when the alarm is tripped. But the sky is the limit. You can hook anything up to the alarm input so long as it acts like a switch. So, glass break sensors, motion detectors, chemical sensors…whatever you wish. The alarm outputs work the other way around. Instead of the alarm telling the Hydoid there’s a problem, the alarm output is designed to drive any 12-volt device like a siren for instance. You can program the software to turn the alarm output on when a particular sensor goes outside a range you specify.

Analog input is actually just a generic input. If you want to measure a sensor that we don’t already include and monitor, you can hook it up here. It’ll accept just about any 0-5-volt analog sensor. So for instance, maybe you want to monitor the moisture content in your drain to waste system. Or maybe you want to datalog the PAR output of your lights over time. We’re sure our customers will dream up ideas that we never even thought of.

So that’s a brief rundown of the Hydroid. If you have any questions about the information presented here please use the comments form below, or feel free to contact us. We appreciate everyone’s comments and feedback. Thanks for checking us out!

As you can see the software can accommodate nearly any kind of growroom device, conditions, or hydroponic setup. We tried very hard to make it as flexible as possible without becoming overwhelming. If you have any questions about your particular setup, and whether the Hydroid can support it please contact us so we can discuss your requirements.

When we started learning about hydroponics this was one particular question we couldn’t get a straight answer. Everyone we talked to had a different answer than the next guy, and sometimes those answers contradicted with each other! We’d like to take a moment to explain why people are so split as to which unit is better to use.

When you stick an EC/TDS probe into a hydroponic solution, all the sensor probe is really doing is measuring the resistance, or how easily electricity flows through the fluid. Pure water does not conduct electricity very well, but as you add synthetic salts as you would in a hydroponic application the electrical conductivity starts to increase. We use this property to determine how much food our plants are being served. Very simply: The more nutrients in the reservoir, the more electrical conductivity you get.

So then when do EC (electrical conductivity) or ppm (parts per million) units come into play?

When you put your EC/TDS probe into your hydroponic solution we said it’s measuring resistance. Okay, then what does that have to do with conductivity? The EC/TDS meter is going to measure the resistance of the solution in Ohms (which is just a unit used to express electrical resistance). As resistance goes up, electrical conductivity goes down and vice versa. We call this an “inverse relationship,” and like the name implies all we have to do to calculate conductivity is take the inverse of resistance. So for instance, if our EC/TDS meter measured the solution as 500 Ohms, then it has to convert that value into conductivity:

Notice the “S” after the 0.002. That stands for “Siemens,” which is the unit used to express electrical conductivity. You can see how simple it is to compute. The only caveat is that most people don’t run their nutrients strong enough to reach 1 Siemen (sea water isn’t even 1S) so they usually multiply the value by 1000 to get a less cumbersome number. When we do this we get 2.000mS, or two “milli-Siemens.” Multiply the number by 1000 again and you get 2000uS, or two thousand “micro-Siemens.” All are equally acceptable units used to express electrical conductivity, and hence nutrient concentration.

1 Siemen (S) = 1,000 milli-Siemens (mS) = 1,000,000 micro-Siemens (μS)

or

1 micro-Siemen (μS) = 0.001 milli-Siemens (mS) = 0.000001 Siemens (S)

So what about ppm? ppm stands for “parts per million” and actually has no direct relationship with electricity. People typically use ppm to quantify trace amounts of “stuff” within a volume of some “other stuff” that is otherwise pure. For example, if I had a million glass marbles, and the concentration of white marbles among the group was “1ppm”, that just means for every 999,999 black marbles, I have one white one. So how does that relate to hydroponics?

We established that the salts in nutrient solutions increases electrical conductivity as the concentration increases. The problem is that statement is too vague because different salts have different conduction properties!! So for instance, 1000 parts per million of table salt in pure water would have different electrical conductivity than say, 1000ppm of potassium chloride in pure water. This illustrates one of the great downfalls of using ppm to express nutrient concentration: YOU MUST SPECIFY WHICH SALT YOU’RE MEASURING! If someone tells you to add nutrients into your hydroponic system until it reaches some ppm value, your next question should be, “ppm of what?”

In a nutshell, the problem with using ppm to quantify nutrient strength is that it requires an extra and arguably useless conversion in order to calculate it, and this gets very confusing for people. We already know how conductive our solution is, which is indicative of our nutrient concentration, and that’s what we actually care about. However, TDS meters add an extra step based on the assumption that you’re only interested in measuring one particular type of salt. Some meters are calibrated to measure the salt sodium chloride (NaCl), and assume you’re running that. Other meters are calibrated for potassium chloride (KCl), and some meters are calibrated for 40% sodium sulfate, 40% sodium bicarbonate and 20% sodium chloride (442). To make matters worse, sometimes the type of salt a TDS meter is calibrated for isn’t plainly obvious. And sometimes nutrient companies don’t even declare which ppm conversion value they expect you to use. And sometimes people refer to different conversion factors by the big companies that use them like, “The ‘Hanna’ conversion factor.” AHHHH!!!! This is way more trouble and confusion than it’s worth!

Let’s walk through an example to illustrate the point. A TDS meter is calibrated to measure the concentration of NaCl, which carries a conversion factor of 0.5. If the meter measures the nutrient solution to be 500 Ohms, what is the resulting ppm value?

Note above that all we did was calculate the electrical conductivity in micro-Siemens, and then we applied the conversion factor of 0.5 to get to ppm.

Okay, so what if the meter was calibrated for 442?

Again, all we did was calculate the electrical conductivity in micro-Siemens, and then applied the 442 conversion factor of 0.7.

Take notice of how both measurements are represented in “ppm” but you can see the difference between the two is nearly 30 percent! All it takes is a vague nutrient product label or a poorly marked TDS meter to screw this conversion up and unwittingly stress your plants. This is exactly why Grohaus Automation prefers to use electrical conductivity to express nutrient concentration. There’s only one type of electrical conductivity: Siemens. Unlike ppm, which can have several different interpretations and conversion factors, electrical conductivity is always the same no matter what type of salt you’re measuring. 1mS will always equal 1mS, no matter what you’re measuring.

So if measuring TDS is so terrible then why is it the industry standard in North America? The problem is cyclical like a mobius strip. Manufacturers use TDS because they think that’s what their customers want, and customers use TDS because that’s what the manufacturers use. The majority of growers in Europe know what’s up, and they use EC to represent nutrient concentration. If North American consumers made enough of a stink about how cumbersome it is to use TDS then the big manufacturers would probably change their convention. They want to make customers happy, after all.

Grohaus Automation is giving it’s own subtle push in the right direction. Our Hydroid control system’s user interface defaults to EC for all nutrient concentration measurements. You can of course change this to ppm (either 0.7 or 0.5 conversion factors), but we’re trying to get people used to looking at EC values. We feel strongly using EC will result in less feeding mistakes, but we also strongly believe in giving people options! So choose which one works best for YOU and stick with it.

Have an opinion on the matter? We’d love to hear your two cents! Head over to the Grohaus Automation forum and sound off…

As you can see the software can accommodate nearly any kind of growroom device, conditions, or hydroponic setup. We tried very hard to make it as flexible as possible without becoming overwhelming. If you have any questions about your particular setup, and whether the Hydroid can support it please contact us so we can discuss your requirements.