Team:Newcastle/Circuitry
Alternative Roots
Circuitry
Stage One
Powering
There is two options for powering this device via the mains or from a battery source. I have designed it so both can be used if the other isn’t available. However I would recommend using the mains as batteries need to be replaced regularly. Since the Arduino and LED lights need a constant 5V supply once the batteries have drained to roughly 3.5V the lights start to fade and do not operate as designed. Also we used 4 cheap AA 1.5V which totals to 6V, meaning a voltage regulator is needed to protect the circuit. This regulator can get hot after sustained use, I believe this is due to the lights drawing 1.5 Amps. However for a small demonstration this is sufficient. Therefor a more permanent and reliable source would be the mains. Taking a regular phone charger which safely steps the voltage down to 5V we have a power source for the Arduino to use. I would not recommend building your own. Usually there is live (Vdd), ground (GND), and two data lines (-D, +D) the latter two are not necessary for our application. When powering the Arduino a capacitor is needed to put in parallel, this protects it from surges in voltage which could otherwise damage it.
Schematic of a standard USB cable [1]
Schematic of a standard USB cable [1]
ROUGHLY
AMPS ARE PULLED
FOR THE WHOLE SYSTEM
APPROXIMATELY
KWH OF POWER ANNUALLY
USED TO POWER SYSTEM
PROVIDES UP TO
LUX OF LIGHT
TO GROW SEEDS
CONTAINS
INDIVIDUALLY ADDRESSABLE
LOW-POWER LED'S
Stage Two
Control
There was a number of ideas on how to control the day and night cycle (16-8 hours), one method would break the circuit from the ‘Vdd’ line (power line). We decided to pursue this method as we were under the impression this would reduce the power consumption when the night cycle was in effect.
In order to break the power line needs to be two pin outs, pin 11 for the data line and 12 for the switching circuit. 11 determines the light intensity and function of the lights. After a 16 hour cycle pin 12 is written to ‘LOW’ (logic zero), which turns the N channel power MOSFET off for 6 hours. This sequence repeats every day. The code can be seen in here.
There was some issues when implementing this design. Which appeared to be caused by the Arduinos pin out voltage, 3.3V. Going of the MOSFET’s data sheet the threshold is between 1-2V [1]. Therefor for our purpose it should be adequate however the voltage at the source (MOSFET) was measured to be 3V, the LED’s need at least 4.2V.
Meaning we had to go back to the drawing board secondly, we looked at using a NAND gate. There is a truth table included to describe the function.
| Vdd | Pin 12 | Output |
|---|---|---|
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 1 |
Highlighted in red is the two functions we are interested in. Since ‘Vdd’ will always be read as ‘high’, 5V. We can eliminate the first two states and ‘Vdd’ making the logic straightforward. The basic operation is inverting P12 logic. This method worked in theory however in practice the LED’s demanded too much current up to 2A, leading the gate to heat up to an unsustainable level. Thirdly we attempted to implement a relay switch however this was also limited on current. Finally, we discovered we can achieve the desired result through the code. Changing the brightness from a defined integer, to an 8 bit integer allowing a range between 0-255. Setting the brightness to ‘0’ would turn the LED’s off.
The engineers, hard at work trying to troubleshoot issues with the system.
The finished product, set to a rainbow function that cycles through various wavelengths of light
Stage Three
LED Wiring
Substantial time was spent carrying out extensive research, both inside and outside the lab, in order to optimise the system for the target audience. This included speaking with organisations and individuals in industry who are involved with hydroponics-based systems or those who may be interested in working with such a system in the future. Some of the individuals we liaised with include Chris Tapsell, the Research Director of KWS UK, one of the biggest seed companies in the world, and Richard Ballard, co-founder of Growing Underground in London where they hydroponically grow micro greens and salad leaves 33 metres below the ground. These potential clients helped us focus our product so that it can better meet the needs of our clients.In addition to gathering external opinion on our system, we also did our own tests on system performance. This included tests to verify the optimal light intensity, wavelength and positioning. The graph below illustrates how the light intensity (measured in lux) varies over time (in seconds) when the system is operated under various wavelengths of light. The black line indicates the system running with the rainbow function loaded which cyclically varies the light wavelength. As the results showed that blue, red and purple light and provided the most lux we are currently using these in the system but plan to use the rainbow function too in future to see how this affects growth or the aesthetics of the plant.
