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Using Electronic Modules with Jim Rowe UVM-30A Module Ultraviolet Light Sensor This ultraviolet (UV) light-sensing ‘breakout’ module detects the intensity of UV solar radiation and hence the degree of protection you may need to prevent skin damage. If you connect it to an Arduino or other microcontroller, it can even indicate the current ‘UV Index’. P rotection is critical if you spend a lot of time outdoors during daylight hours (sunscreen, hat etc) to avoid sunburn and to lower your chances of developing skin cancer. The UVM-30A analog UV light sensing module is ideal for detecting harmful UV rays and can be used to build your own UV sensor. It easily connects to an Arduino or other microcontroller unit (MCU) and with the right firmware, it will indicate the current UV Index or ‘UVI’. If you’re unsure what this is, please see the “UV Radiation and the UV Index” panel. Sunburn and skin damage are caused by the UV wavelengths in solar radiation, which can still be quite strong even when the sky is overcast. So checking the UV radiation level is still important. UV radiation varies in strength during the day, just like visible light and infrared (IR) heat radiation. As with these other wavelengths, its intensity tends to follow a bell-shaped curve, with the peak at the middle of the day or soon thereafter. So it can be worthwhile to keep tabs on the UV radiation level if you are going to be outdoors, even in the early morning or late afternoon. At the heart of the UVM-30A module is a miniature UV sensor called the GUVA-S12SD. This is in an SMD package measuring 3.5 × 2.8 × 1.8mm and is made by Genicom Co Ltd in South Korea. Genicom describes it as a schottky-­ type gallium nitride photodiode designed to respond to UV radiation with wavelengths between 240 and 370nm (nanometres). It is also described as being ‘blind’ to visible light. The response curve of the GUVAS12SD sensor is shown in Fig.1. Its sensitivity is very low at wavelengths below 240nm, rising steadily to a peak at 350nm before dropping sharply between 360nm and around 375nm. So it has good sensitivity over the UV-B range from 280nm to 315nm and even better sensitivity over slightly more than half of the UV-A range, from 315nm to 365nm. The vertical units in Fig.1 are microamps per milliwatt of UV radiation. The Genicom data sheet for the GUVAS12SD lists the typical peak response of the device as 0.14A/W at 350nm, equivalent to the peak of the curve in Fig.1. The UVM30A module is comprised of a larger PCB (28 × 12.5mm) and a smaller PCB (3.5 × 2.8mm). The smaller PCB hosts the GUVA-S12SD UV sensor in a white SMD package. Fig.1: the sensitivity of the GUVA-S12SD sensor to light within the UV spectrum. The x-axis is the light wavelength in nanometres, while the y-axis shows the microamps conducted per milliwatt of incident radiation at that wavelength. This indicates that it’s most sensitive to UV-A but will also pick up much of the UV-B spectrum and some UV-C, at reduced sensitivity. siliconchip.com.au Australia's electronics magazine This image is shown at 250% actual size. May 2023  43 Inside the module Fig.2: the circuit of the UV sensor module is pretty straightforward. A bias voltage is applied to the photodiode from the op amp output via a resistor, converting the current into a voltage that’s fed to the OUT pin. The yellow box surrounds the components on the sub-PCB; the main PCB just adds a bypass capacitor and the 3-pin SIL header with two power pins (+ and −) and the analog output. As shown in the circuit diagram, Fig.2, there’s very little in the UVM30A module apart from the GUVAS12SD sensor (PD1), and a small SGM8521 op amp (IC1) used to convert its output current into a voltage. The conversion performed by op amp IC1 conforms to the expression Vo = 4.3 × 106 × Ipd, where Ipd is the current passed by PD1 in amps. So a PD1 current of 280nA should result in an output of 1.2V. Most of the circuitry in Fig.2 is inside a pale yellow rectangle with a dashed red border because that part of the module is on a small subPCB mounted on the larger PCB. The smaller PCB measures only 3.5 × 2.7mm square, while the larger module PCB is 28 × 12.5mm. The only components on the larger PCB are a 10μF supply bypass capacitor and a 3-pin SIL header. Connecting it to an MCU Fig.3: wiring up the module to an Arduino Uno couldn’t be much simpler. Just connect the module’s + supply pin to its +5V, the module’s – supply pin to its GND and the module’s output to one of its analog inputs (in this case, A0, to suit our example sketch). Fig.4: connecting the UV sensor module to an Arduino Nano isn’t much different than the Uno shown in Fig.3. Once again, the module is supplied with 5V from the Nano’s +5V and GND pins while the module’s analog output signal goes to the Nano’s A0 analog input. 44 Silicon Chip Australia's electronics magazine Since the module has an analog voltage output and operates from a DC supply voltage of 3.3V to 5V, it is quite easy to connect to a microcontroller such as an Arduino Uno or Nano. You just need to connect the + and − power pins to the +5V and GND pins on the MCU board, while the “OUT” pin goes to an analog input on the MCU, such as the A0 analog input, as shown in Figs.3 & 4. All that’s needed then is suitable firmware. After searching the internet, I found a website with a graph showing the output voltage of the UVM30A module plotted against the equivalent UV Index (see siliconchip.au/link/ abi0). I’ve redrawn this as Fig.5. On the same website, I also found an Arduino sketch for a UVI sensor, although this sketch was designed to display the calculated UVI level using a Nokia 5110 LCD module. I adapted this sketch into one that displays both the module’s output voltage and the equivalent UVI figure on a low-cost 16×2 LCD module with an I2C serial interface (eg, Silicon Chip Online Shop Cat SC4198). Fig.6 shows how an Arduino Uno connects to both the UVM30A module and the LCD with the I2C interface attached. The resulting sketch file is called “Arduino_UVI_meter_sketch.ino” and is available for download from the Silicon Chip website. When you upload siliconchip.com.au Fig.5: the mapping of the output of the UV sensor to the UV index is primarily linear, except below a UV index of one. Therefore, the formula to convert its output voltage to the UV index is pretty simple. The sketch source code (available for download) shows exactly how it’s down. Shown at right is the Adafruit version of the UV sensor. It uses the same GUVA-S12SD sensor IC as the Altronics version. it to the Arduino, it first gives you this opening display: Silicon Chip UVI Meter Then, after pausing for two seconds, it starts measuring the output voltage from the UVM30A module. It converts the reading into the equivalent UV Index and displays both, like this: UV Index = 2 Vout = 350mV It repeats this every 1.5 seconds. The sketch also sends this data back to your computer via the Serial Monitor (if you have it connected). So it is easy to hook the UVM30A UV sensing module up to an MCU like the Arduino and make yourself a handy UVI meter. The sketch could also be adapted to MMBasic code for use on a Micromite or Maximite; any microcontroller with an analog input should do. One morning in late October, I took this arrangement outdoors and got UVI readings of 1-2 when the Sun was only about 30° above the horizon. The readings steadily rose as the morning wore on (although they dropped back when clouds obscured the Sun). When the Sun was directly overhead and the clouds were not obscuring it, the UVI readings reached a level of 8 or 9. So it appears to be doing its job and should be helpful for those who spend a lot of time outdoors. By the way, the Australian Bureau of Meteorology also publishes UV Index predictions in their forecasts. Of course, they only give a rough idea of what to expect, whereas this module provides a reading of the immediate conditions. Cost and availability I obtained the module shown in the photos from Altronics (catalog code Z6397) for around $40. But I also discovered a smaller version of the module available from several other suppliers. This version has the same circuit, but everything is mounted on a single PCB measuring only 19 × 10 × 2mm and seems to originate from the US firm Adafruit (www.adafruit.com). Adafruit has it (ID 1918) available for US$6.50 plus shipping. But it’s also available from Australian firms such as Pakronics (www.pakronics. com.au) for just under $15 plus shipping, or from Digi-Key in the USA for around the same price. There is yet another smaller version available from various suppliers on AliExpress. This one measures 19.8 × 10 × 2mm and is available for around $6 with free shipping. So you have quite a good range to choose from, all with the same UV sensor and its surrounding circuit, in various sizes and prices. continued on page 46 Fig.6: to make a practical device, I added a serial (I2C) 16×2 LCD module to the basic circuit, wired as shown here. That allows the Arduino to display both the raw UV sensor output voltage and the equivalent UV index in a handy portable package if the Arduino is battery-powered. siliconchip.com.au May 2023  45 UV Radiation and the UV Index Ultraviolet or UV radiation is electromagnetic radiation with wavelengths between 10nm (nanometres) and 400nm – shorter wavelengths than the light that is visible to humans but longer than the wavelength of X-rays. UV radiation constitutes about 10% of the total radiation from our Sun. Still, this radiation is the primary cause of suntan, sunburn and skin damage resulting in skin cancers. The section of the solar UV radiation spectrum primarily of interest regarding human skin safety is between 100nm and 400nm. This is subdivided into three main divisions: UV-A (315nm to 400nm; ‘long wave UV’), UV-B (280nm to 315nm; ‘medium wave UV’) and UV-C (100nm to 280nm; ‘short wave UV’). Although photons of UV-C radiation carry more energy than those of UV-B or UV-A and are therefore more capable of skin damage, the good news is that virtually none of the Sun’s UV-C radiation ever reaches the surface of the Earth. These photons are absorbed by oxygen and ozone in our upper atmosphere. Most of the UV-B radiation from the Sun suffers the same fate, especially when there is heavy cloud cover. When there is cloud cover, more than 95% of the solar UV radiation reaching the surface of the Earth consists of the longer UV-A wavelength. And these wavelengths are of concern when it comes to protecting our skin. So clouds tend to reduce the amount of UV reaching the surface but do not eliminate it; you can still get sunburn on a cloudy day. The UV Index is an international measurement scale used to indicate the intensity of UV radiation in easily understood terms for the ‘general public’. It uses a scale of 11 or more steps, with each step corresponding to an increase of UV radiation intensity of 25mW/m2 (milliwatts per square metre). A UVI of one indicates a UV intensity of 25mW/m2, two indicates an intensity of 50mW/m2 and so on. Fig.7 shows the UV Index on the right and the corresponding UV radiation intensity on the left. The coloured bands indicate the five categories into which the UVI levels are grouped in terms of their ‘risk of harm’ to our skin. SC Fig.7: this shows the five ranges of UV index values that provide some guidance as to the danger of skin exposure under those conditions. It will depend somewhat on your skin pigmentation, but it’s still a good idea to ‘cover up’ at the upper end of the risk spectrum. Raspberry Pi Pico W BackPack The new Raspberry Pi Pico W provides WiFi functionality, adding to the long list of features. This easy-to-build device includes a 3.5-inch touchscreen LCD and is programmable in BASIC, C or MicroPython, making it a good general-purpose controller. This kit comes with everything needed to build a Pico W BackPack module, including components for the optional microSD card, IR receiver and stereo audio output. $85 + Postage ∎ Complete Kit (SC6625) siliconchip.com.au/Shop/20/6625 The circuit and assembly instructions were published in the January 2023 issue: siliconchip.au/Article/15616 46 Silicon Chip Australia's electronics magazine siliconchip.com.au