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Mini Projects #019 – by Tim Blythman SILICON CHIP The BIG Clock If you need a BIG Clock, look no further! It tells the time, is three feet wide and one foot tall (that sounds larger than 90 × 30cm). The BIG Clock has a simple circuit and we think our clever readers will come up with other ideas for using the BIG, bright display we have designed. W e’ve thought for a while that addressable RGB LED strips would be a good way to make a large, bright display. We thought of arranging the strips in rows to create a dot-­ matrix type display, but that would not have been as big as the BIG Clock. It is 90cm wide and 30cm tall, with the active area of the digit display being 65cm wide and 20cm tall. These strips have a connection for power, ground and data in at one end, with a matching connection at the other end for power, ground and data out. Multiple strips can be joined by simply connecting power to power, ground to ground and data out to data in. Many strips can also be cut to shorter lengths; the smaller strips can then be rejoined in the same way. We’re using Jaycar’s XC4390 WS2812B RGB LED strip. It is 2m long and contains 120 RGB LEDs. Thus, there is one LED every 16.6mm. If we had cut this into five strips of 24 LEDs (about the minimum number of rows needed to make a working dot-matrix display), it would be about 9cm tall and 40cm wide. Instead, we have arranged the LEDs as multiple 7-segment digits. If the segments have five LEDs, we can make digits that are each nearly 20cm tall Fig.1 (left): by arranging the strips in this fashion and wiring in this order, the length of wire between each segment is kept short. Photo 1 (right): here is what a single digit (showing a ‘0’) looks like up close. siliconchip.com.au Australia's electronics magazine January 2025  55 Fig.2: this segments order was arranged to simplify the wiring and matches the software mapping of the segments in the BIG Clock sketch. and 10cm wide. The 120 LEDs yield three 7-segment digits, with three segments to spare; enough to make a 12-hour clock display. You can see a video of it in operation at siliconchip.au/Videos/BIG+Clock Photo 1 and Fig.1 show the basic arrangement of a digit. Like smaller 7-segment displays, we have tilted the segments about 10° from vertical. The digits are around 9cm wide and 18cm tall, with the segments each about 8.3cm long. Fig.1 also shows the way we have wired the segments in each digit. You can see that this keeps the wiring quite short and tidy. Fig.2 shows the pattern we used to wire all the segments of the digits on our BIG Clock, with the output of one numbered segment going to the input of the segment numbered one higher. We used two spare segments to create a leading ‘1’ (#1 & #2) to show hours up to 12. This leaves a single segment spare, which we used as a dash (#10) to separate the hours and minutes. Circuit details The LEDs are controlled by an Arduino Uno WiFi R4 microcontroller board. Its inbuilt WiFi radio can be used to fetch the time using NTP (network time protocol) from the internet. To provide a discreet (and discrete) interface, we added a magnetic reed switch to allow daylight savings to be switched off and on. The circuit is pleasingly simple. All we need is a microcontroller to provide the necessary serial signal to produce the clock display. This digital signal comes from the A0 pin. Although it can be used for analog functions, we have used it as a digital output since it is close to the other (5V and GND) pins needed to drive the LEDs. The reed switch is connected between A2 and GND; an internal pullup means this pin is high unless a magnet is nearby, when the switch shorts the pin to ground. Fig.3 shows the circuit. Construction Laying out and connecting the segments is the most time-consuming part of the construction process. If you want to test the LEDs before or during assembly, jump forward to the Software section so that you can load up the libraries or a test sketch to do so. We used a 900mm x 600mm sheet of Corflute cut in half lengthwise, giving a panel 300mm tall and 900mm wide. Corflute is like corrugated cardboard but made from plastic. The corrugations run parallel to the long side, which is helpful when sketching out your plans. Fig.4 shows the critical dimensions of a single digit and its relation to adjacent digits. Using a plastic substrate means that you can use an erasable Fig.3: the circuit of the BIG Clock is simple; the microcontroller board provides power and data to a series of addressable LEDs. A magnetic reed switch provides a digital input that can be used to toggle the daylight saving mode. 56 Silicon Chip Australia's electronics magazine siliconchip.com.au Photo 2: much of the wiring is hidden at the back of the panel. If you have kept the other half of the Corflute sheet, it could be used to make a rear panel to hide the wiring. marker to demarcate the locations and remove them later. Find the centre of the panel and mark the corresponding horizontal and vertical lines. Add horizontal lines 9cm below and above the centreline. Similarly, add vertical lines 15cm and 30cm to the left and right of the centre. These will allow you to use Fig.4 to sketch the outline of each digit. Next, mark out the holes needed for each digit (the green dots in Fig.4). Note that not all locations require holes! The centre position, for example, will only need holes for the central segment, as it only shows a dash. Double-check the segments against the photos as you go. Cut the LED strip into sections with five LEDs. Be careful to leave some visible copper on each side to allow soldering. The first and last segments come with fixed wiring attached, so they will have to go in the locations marked 1 and 24 in Fig.2. We found that attaching the wires was a bit tricky, since the conformal coating applied to the board inhibits soldering, although it can be soldered through with patience and ventilation. We suggest wiring the segments in groups of seven (for the three full digits) using short pieces of wire (about 5cm). For each connection, join 5V to 5V, DO to DIN and GND to GND. If you cut narrow slots in the Corflute as marked by the cyan lines in Fig.4, you can slot these short wires in from the front, so they are hidden. Then, you only need to make the longer joins between the segments; the longer lengths will allow a bit of room to manoeuvre the strips into a position to allow wiring. Take your time, ensure that the strips go in the correct locations and that wiring flows in the direction of the arrows marked on the strip and in the siliconchip.com.au order shown in Photo 1. Don’t be afraid to hook it up to test that the segments wired so far are working correctly. Photo 2 shows our layout from the rear of the panel. Once everything is roughly in place, remove the backing paper from the adhesive on the strips and press them against the Corflute. There are extra red and white (power) wires at each end. We connected these with insulated wire and heatshrink tubing to provide an extra power feed and to terminate the loose ends. We cut the extra set of three wires short so that they would not get in the way or contact anything else. Uno WiFi R4 wiring We plugged an 8-way header into the headers on the Uno WiFi R4 as shown in Fig.3 and Photo 3. Remove the middle two pins by pulling them out with pliers. This will prevent an inadvertent connection to VIN, since the LEDs only work with 5V supplies. When bending the leads of the reed relay, avoid straining them where they enter the glass envelope, or it can break. We suggest you grasp the lead with pliers close to the body, then bend it, so that no bending force reaches the glass. Solder the wires as shown in Fig.3 and plug the header into the main board. The wire colours on the LED strip might be different; ours had red for 5V, white for ground and green for data. Photo 3 shows that detail on our build. Fig.4: use these dimensions to sketch out the segments on your Corflute before making the holes marked in green. Their size is not critical; about 5mm should work well. The cyan lines indicate slits that can be used to feed the wires through from the front of the panel. Australia's electronics magazine January 2025  57 Parts List – Big Clock (JMP019) 1 Arduino Uno WiFi R4 microcontroller board [Jaycar XC9211] 1 120 RGB LED addressable strip [Jaycar XC4390] 1 magnetic reed switch [Jaycar SM1002] 1 8-pin header, 2.54mm pitch [cut from Jaycar HM3211] 3 1.5m lengths of insulated wire in different colours [Jaycar WH3032] 1 600mm x 900mm sheet of Corflute or similar [Bunnings 0390160] 1 short length of double-sided tape to secure the Uno WiFi R4 [Jaycar NM2821] 1 reel of electrical tape to secure loose wires 1 10cm length of 3mm diameter heatshrink tubing 1 magnet to operate the reed switch 1 USB-C cable to suit the Uno WiFi R4 Secure the Uno WiFi R4 to the Corflute using double-sided tape, and secure loose wires with the electrical tape. Software Arduino IDE needs to be installed and the Arduino R4 board profile selected. This can be installed by searching for “R4” in the Boards Manager and then clicking install. The Adafruit Neopixel library is also required; we’ve included it in the software download package (siliconchip. au/Shop/6/530), along with the sketch file. You can also search for “neopixel” in the Library Manager to find it. There are several sketches under the Neopixel examples (and one in the Jaycar XC4390 data sheet); you just need to change the LED_PIN to A0 and the LED_COUNT to 120. These are a quick way to test that the display is functional. Open the BIG_CLOCK_UNO_R4_ WIFI sketch and change the WiFi credentials at the top of the sketch. There are other parameters that can be changed, but that should be enough to check that all features are functional. Upload the sketch after selecting the correct board and serial port from the menus. The Serial Monitor will report the Clock’s status (115,200 baud); a typical boot sequence is shown in Screen 1. The LEDs should all switch on for two seconds, then normal operation will start. If you see an E0 message on the LEDs, the WiFi connection has failed. E1 indicates that the time has not been updated. Table 1 also lists some commands that can be entered at the serial monitor. Customisation There are a few things that can be changed in the sketch code. The standard time zone offset (in minutes) is set by STD_TZ_OFFSET. The daylight saving adjustment (effected by using a magnet on the reed switch) is one hour. The colour of the lit LEDs is set by Connected IP address: 192.168.0.15 Checking UTP on connection Starting NTP check UDP packet sent 25ms round trip. Packet received Time OK UTC is 2024-09-11T04:39:20 Time is 2024-09-11T14:39:20 Time is 2024-09-11T14:40:00 Time is 2024-09-11T14:41:00 Time is 2024-09-11T14:42:00 Screen 1: this shows a normal startup on the Serial Monitor. The IP address and round trip time are not important. Other messages may appear automatically or if the commands from Table 1 are run. the CLOCK_COLOUR #define; you can use the values given or provide RGB triples. The brightness dictates the current draw, which peaked at 700mA for a BRIGHTNESS setting of 70 on our prototype. Check your supply capabilities and adjust this to suit. If you have Arduino experience, you can also modify the LED layout or mapping. The digits array is a C++ struct (with type seg7_t) for each digit. The struct’s first item is the number of pixels for each segment, followed by the first pixel of each segment in order from ‘a’ to ‘g’. For example, with just four LEDs per segment, you could have 30 segments, giving a full four 7-segment digits plus a couple of segments to spare; enough to count up to 19999. We think the white Corflute looks smart but it doesn’t give a lot of contrast against the LEDs. When we get the chance, we plan to paint the Clock’s background a flat grey to make the SC numbers stand out more. Photo 3: an 8-pin header with the two central pins removed is used to connect the wiring to the Uno WiFi R4. The green wire at right carries data to the DIN pad of the first LED pixel. When completed, the Big Clock is three feet (900mm) wide and lights up the room. We think it will give our readers some great ideas for creating other large displays. Table 1: serial commands 58 Silicon Chip Australia's electronics magazine Command Action u Force NTP time refresh r Reboot processor t Make time invalid 0 Turn off daylight saving 1 Turn on daylight saving siliconchip.com.au