LED Technology


Figure 4: With the SparkFun Qwiic adaptor, developers can easily add custom circuits through Qwiic connections with the Pioneer add-on shield, or by using the provided headers to stack the adaptor with the add-on shield on Pioneer boards. (Image source: SparkFun)


SparkFun Electronics and Digi-Key Electronics. The PSoC Pioneer IoT add-on shield is an Arduino R3-compatible shield with Qwiic and XBee-compatible connectors (Figure 2). Plugged into a PSoC Pioneer board, the add-on shield lets developers easily extend the board set with devices such as sensors for monitoring air and soil quality in a greenhouse. For monitoring greenhouse ambient conditions, a Qwiic-compatible board such as the SparkFun SEN-14348 Environmental Combo Breakout board uses the onboard Bosch Sensortec BME280 and ams CCS811 sensors to provide data for multiple environmental variables (see, “Add Compensated Air Quality Sensors to the Internet of Things”).


The Bosch BME280 combines digital sensors able to deliver accurate readings on temperature, pressure, and humidity while consuming as little as 3.6 A at a 1 Hz update rate. The ams CCS811 provides equivalent CO2 and total volatile organic compound (VOC) measurements.


Gas sensors such as the CCS811 need to heat an internal hotplate to perform gas measurements, causing power consumption to rise accordingly, reaching 26 milliwatts (mW) from a 1.8 volt supply in its operating mode 1. This mode provides the fastest available update rate of 1 Hz. Developers can choose other update rates such as mode 3, which performs measurements once a minute and reduces power consumption to 1.2 mW. Developers simply use a Qwiic cable to connect the Combo board to the add-on shield to program the Combo board's Bosch BME280 and ams CCS811B sensors based on sample software available in the SparkFun github repo.


Soil quality


Besides ambient conditions in a greenhouse, proper soil pH and water content are essential for plant health. Most plants require soil pH levels that are neutral or only slightly acidic, but the optimal pH range can vary significantly. For example, potatoes grow best in acidic soils with a pH of around 5.5, whereas this level can damage plants like spinach that prefer slightly alkaline soils.


At the same time, small changes in pH level, even within the optimal range, can directly affect the availability of nutrients needed to sustain growth (Figure 3). Developers can easily add pH sensing to


their greenhouse systems using the SparkFun Electronics SEN-10972 pH Sensor Kit. The kit comes with a pH probe, interface board, and buffer


www.cieonline.co.uk


solutions for calibration. For communicating with the PSoC microcontroller, developers can use the default UART output from the pH board. Alternatively, the pH sensor board can be used in I2C mode and connected through the SparkFun DEV-14495 I2C Qwiic adapter. The SparkFun Qwiic adaptor breaks out the I2C pins from the Qwiic connectors and provides solder points allowing developers to easily use existing I2C devices with the Qwiic connector system. Measuring soil water content is just as


easy. The SparkFun SEN-13322 Soil Moisture Sensor provides two exposed pads designed to sit directly in the soil and serve as a variable resistor between a provided voltage source and ground. Higher moisture content increases conductivity between the pads, resulting in a lower resistance and higher voltage output. For this sensor, the PSoC


microcontroller's integrated digital-to- analog converter (DAC) can be used as the voltage source, and its successive approximation register (SAR) analog-to- digital converter (ADC) can be used to digitize the voltage corresponding to the soil’s moisture level. Also, the microcontroller's internal op amps can be used to buffer both the DAC output and the ADC input.


Horticultural lighting with LEDs As noted earlier, plant health depends on light illumination delivered at specific wavelengths. Although advances in LED lighting have delivered solutions for industrial lighting, vehicle headlights, and more, conventional LEDs have lacked the spectral characteristics required for photosynthesis. The Wurth Electronics WL-SMDC series of mono-color ceramic LEDs addresses the need for illumination at wavelengths ranging from deep blue to hyper red (Figure 5). Used in combination, the SL-SMDC


series provides the wavelengths needed to promote numerous aspects of plant growth.


The 150353DS74500 deep blue LED (450 nm peak wavelength) and 150353BS74500 blue LED (460 nm dominant) provide illumination in the range of wavelengths associated with regulation of chlorophyll concentration, lateral bud growth and leaf thickness. The 150353GS74500 green LED (520 nm peak) and 150353YS74500 yellow LED (590 nm dominant) provide illumination in a range of wavelengths once considered unimportant, but now known to play a part in shade avoidance responses in plants.


harmful intensity levels to reach the retina. The use of constant current LED drivers, such as the Allegro ALT80800, help mitigate this effect.


Software design


Used in combination, the PSoC Pioneer board, add-on shield, and additional boards mentioned earlier, enable developers to physically build a greenhouse control system largely by plugging the hardware boards together. Development of software for managing sensors or driving LEDs is nearly as simple with the availability of components in the Cypress peripheral driver library (PDL).


PDL components abstract the functionality of PSoC features such as programmable analog, UDBs, and Smart I/O peripherals. Developers can quickly implement a software feature that causes the microcontroller to wake when the sensor output reaches a particular level. For example, when the output voltage from the soil moisture sensor indicates drier soil, using Cypress PSoC Creator, developers can configure one of the PSoC microcontroller's integrated low-power comparators to generate an interrupt when the level on the specific analog pin falls below (or above) a reference voltage level.


Figure 5: Individual members of the Wurth Electronics WL-SMDC series of mono-color ceramic LEDs provide illumination at specific wavelengths required for plant growth and development. (Image source: Wurth Electronics)


Developers can further extend their soil management capabilities with this same approach. For example, the PSoC 6 microcontroller supports multiple channels on both the DAC output and the ADC input, making it feasible to add multiple pH sensors. In addition, some applications may require greater resolution measurements that require a voltage range beyond the microcontroller's 3.6 volt (max) VDDA analog supply voltage. In these instances, the solution lies in adding external buffer op amps and a voltage regulator. Along with measuring soil water content, ambitious developers can use the same approach to automate water irrigation by using the PSoC's GPIOs and pulse width modulation (PWM) functionality to control a DFRobot FIT0563 water pump with a DFRobot DRI0044-A driver board.


For additional components, such as these or others, use the SparkFun DEV- 14352 Qwiic adaptor. This provides Qwiic connectors and a large prototyping area (Figure 4).


As the Qwiic adaptor conforms to the


Arduino R3 shield layout, developers can use the headers included with the Qwiic adaptor kit to stack their own circuits between the Pioneer kit board and the SparkFun IoT Pioneer add-on shield.


The 150353RS74500 red LED (625 nm dominant) and 150353HS74500 hyper red (660 nm peak) provide illumination at the wavelengths most involved in photosynthesis, but also involved in different plant stages including flowering, dormancy, and seed germination. The 150353FS74500 far red (730 nm


peak) provides illumination at wavelengths associated with plant germination, flowering time, stem length, and shade avoidance. Finally, the 158353040 daylight white not only augments blue wavelength coverage, but also contributes to the overall daily light integral (DLI) levels needed for overall plant growth. Developers can find a number of LED drivers such as the Wurth MagI3C 171032401, or the Allegro MicroSystems ALT80800 to drive strings of the LEDs. Many of these devices support dimming regulation using PWM and/or analog voltage, reducing LED driver


implementation to only a few additional components.


In designing a dimming feature,


however, developers should be wary of very rapid changes in instantaneous illumination level. At high PWM rates, the human pupil may respond only to average light intensity, permitting pulses of light at


Developers can similarly employ other PDL components to support other interface and control requirements with minimal code development. For deployment in a larger greenhouse


environment, a cost-effective approach would distribute features such as soil pH measurement and ambient temperature measurement in ground-level board sets, using separate board sets to control the horticulture LED strings.


Conclusion Automated greenhouse control systems used to require industrial-grade controllers linked to complex lighting systems, sensors, and actuators. As shown, developers can now take advantage of low-cost microcontroller boards and add-on boards to build cost-effective platforms able to leverage a broad array of available sensors and actuators.


Combined with the IoT and the availability of specialised horticulture LEDs, developers have a full complement of components required to implement sophisticated applications able to remotely monitor and control many of the factors associated with healthy plant growth and development.


digikey.com Components in Electronics February 2020 13


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76