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Max’s Cool Beans By Max the Magnificent Flashing LEDs and drooling engineers – Part 19 I ’m so excited I want to run round in ever-decreasing circles shouting, ‘Don’t Panic!’ I first read the seminal Foundation trilogy (Foundation, Foundation and Empire, and Second Foundation) by Isaac Asimov when I was a young lad, and I’ve re-read them on multiple occasions ever since then, but never did I dare to hope that these masterpieces would one day be brought to life on the big (or small) screen. So, you can only imagine my surprise and delight when, earlier this year, I became aware that Apple TV+ was working on the Foundation TV series. Even better, just a few moments before I started penning these words, I heard that this series is set to launch on 24 September 2021. Now, all we have to do is wait in antici... ...pation! What we need is something to take our minds off things as we wait. I know what we can do. While we are twiddling our thumbs, we can pass the time talking about 21-Segment Victorian displays and SMADs (Steve and Max’s Awesome Display) boards. God save the Queen! Let’s start by reminding ourselves that Steve Manley in the UK and your humble narrator in the US are both creating 10-character versions of the 21-segment Victorian displays we introduced in earlier columns (PE, July and August 2021). The patent for the original display was first filed in 1898 when Queen Victoria was the ruler of all she surveyed (and quite a lot beyond her window). In those days of yore, the illumination was provided by 21 small incandescent bulbs, while the control was afforded by a cunningly complicated contrivance of electromechanical complexion. In our case, each display segment boasts one or two tricolour LEDs (Fig.1), while our control functions will be afforded by a microcontroller. It goes without saying (but I’ll say it anyway) that our displays are going to boast myriad capabilities, including being able to react to random sounds and music, but much of the time they will be presenting alphanumeric information such as the time, date and a variety of text-based messages. Is that the time? So, what can we do with 10 characters? Well, one obvious application is to display the time in hours, minutes, and seconds along the lines of 08:16:20. In this case, we require only eight characters (six numbers and two colons), which we could centre on the display (Fig.2a). One of the options we will provide is to present the time in 12-hour (eg, 08:16:20) or 24-hour (eg, 20:16:20) formats. The abbreviation AM (or am or a.m.) stands for ‘ante-meridiem’ (before the Sun has crossed the meridian line), while PM (or pm or p.m.) stands for ‘post-meridiem’ (after the Sun has crossed the meridian line). Now, I don’t know about you, but I’m usually cognisant as to whether I’m currently in the AM or the PM, so I’m reasonably confident in my ability to work things out if my time is displayed 08 : 16 : 20 (b) 0 8 : 1 6 : 2 0 P (c) 2 0 2 1 / 0 9 / 0 1 (a) Fig.1. Map of LEDs (numbers) and segments (letters) (Image source: Steve Manley) 44 (d) 01 / 09/ 2021 (e) 09 / 01/ 2021 Fig.2. Time and date format alternatives. in a 12-hour mode. On the other hand, some users may prefer a more explicit presentation, and we always have to remember that things could become somewhat confused in the event of a zombie apocalypse, so we could also offer the option to indicate ‘A’ (AM) or ‘P’ (PM) while in 12-hour mode (Fig.2b). Want a date? When I was a kid, my parents used to serve a variety of nibbles to visitors over the Christmas holidays. In addition to a selection of nuts and pastries, they also used to serve dates. Since I only saw these tasty treats once a year, and as I was aware they originated in exotic Middle Eastern climes, I thought that these sweet fruits were really, really special, but that’s not the sort of date we’re interested in here. When it comes to presenting the date in a chronological sense, the format I use with regards to naming files and folders on my computer is YYYY/MM/DD with leading zeros as required (eg, 2021/09/01) (Fig.2c). For a variety of reasons this is the most logical format to employ, which probably explains why its usage is relatively uncommon (humans; bless their little cotton socks). The next logical alternative is to flip things around and use DD/MM/YYYY, which places the values in order of immediate significance to the viewer (Fig.2d). Finally, for reasons that escape my powers of description, we have the MM/DD/YYYY format that is commonly used in the US (Fig.2e). It obviously makes sense for us to offer our users the ability to select between the three aforementioned formats when 2021 / 09 / 01 (b) 2 0 2 1 / 0 9 / 0 1 (a) (c) 2021 / 09 / 01 09 / 01/ 2021 (e) 0 9 / 0 1 / 2 0 2 1 (f) 0 9 / 0 1 / 2 0 2 1 (d) Fig.3. Alternative ways of setting the date. Practical Electronics | September | 2021 Fig.4. Pseudo-brass front panels (Image source: Steve Manley) it comes to displaying the date, but this leads us to consider how our users are going to set the date in the first place. On the one hand, we could allow the user to enter any old values in any old order, setting the day to be 66 and the month to be 42, for example, but that really doesn’t make much sense. What does make sense is to allow (force) the user to enter only valid values. Since the number of days in the month depends on which month we are talking about, this means that we must persuade the user to specify MM before DD. Similarly, since the number of days in February depends on whether or not we are in a leap year, it makes sense for us to force the user to enter the date starting with YYYY followed by MM followed by DD. Let’s assume that the user has previously specified that the date should be displayed in the American MM/DD/YYYY format (Fig.2e). One solution when it comes to setting the date is to revert to the YYYY/ MM/DD format and guide the user to enter the values in the correct order (Fig.3a, 3b, 3c). For example, we could implement a cursor effect by flashing the current character of interest (CCOI). Or we could make the CCOI bright while dimming the other characters, or we could make the CCOI one colour and the other characters another colour, and – of course – we could use any combination of these effects. On the other hand, if the user has expressed a preference with regard to the way in which the date should be displayed, who are we to compel them to use a different format when it comes to setting the little rascal? Using any combination of the cursor techniques we just discussed, we could leave the display in MM/DD/YYYY mode while still guiding the user to enter the new date in the order YYYY then MM then DD (Fig.3d, 3e, 3f). Can you think of another possibility? I just did. My alternative suggestion is at the end of this column. Why, oh why? You may be wondering why we are talking about things as mundane as displaying and setting the date and time. Well, the problem is that a lot of people don’t take the time (no pun intended) to think this sort of thing out before they leap into the implementation. As an example, I have yet to successfully set the clock in my new (2019) car. I’ve perused and pondered the manual and I’ve fought my way through myriad layers of nested menus, but successfully updating the display has defied me. It shouldn’t be so hard. I’m the leading engineer in my generation* for goodness’ sake (* should you doubt this statement, may I refer you to my dear old mother who will be delighted to help you see the error of your ways). The point is, at some time in the future, you may end up creating some sort of system that has to allow the user to set and display some form of information. My hope is that our discussions here will aid you in your endeavours and make the radiance of your users’ smiles lighten your life. I #### YOU Fig.5. Analogue/digital multiplexer (Image source: SparkFun) Practical Electronics | September | 2021 I don’t think I’ve shown you a representation of the two laser-cut pseudo-brass front panels I’m using as part of my 10-character display (Fig.4). Steve wasn’t interested in the bottom panel, but he kindly created the design files for me, after which my chum Kevin McIntosh, who is the owner of The Laser Hut in the UK (https://bit. ly/2RqQ1Zj), used his laser to cut them out for me. So, what’s with the bottom panel? Well, some time ago I was introduced to an interesting article and video showing a piece of word art that was created by Matt Gorbett in 2007 (https://bit.ly/2THZLQf). This piece involved eight characters and two spaces that spelled out ‘I #### YOU’ (when you include the spaces, this would consume all 10 of the characters in my display). In Matt’s implementation, there are four potentiometers located below the four #### characters. Passersby can use the potentiometers to select letters to complete the message, such as ‘I LOVE YOU’. After some period of time, the system starts swapping individual letters to form related messages until eventually returning to its ‘I #### YOU’ state. In my case, in the spirit of overengineering everything, I decided to have potentiometers associated with each of my characters. Of course, this potentially means I’m going to require 10 analogue input pins on my microcontroller. Unfortunately (or fortunately, depending on your point of view), when purchasing my potentiometers, I didn’t pay as much attention to the online ordering system as perhaps I should. As a result, it was only when the little scamps arrived that I discovered they had associated switches. Well, ‘waste not, want not,’ I thought, but this potentially means that I’m going to require 10 digital input pins on my microcontroller, which means 20 pins in all (sad face). Fortunately, the clever guys and gals at SparkFun have us covered with a rather cool 16:1 analogue/digital multiplexer breakout board (https://bit.ly/2TPFY1a – see Fig.5). Using only four digital output pins on the microcontroller, we can select one of the sixteen analogue signals from 45 Seeing eye to eye Fig.7. An exploded view of the Owl Glasses display (Image source: Steve Manley). The wonderful thing about SMADs is that you can create an awesome display using just one board. Having said this, much like eating crisps (‘chips’ in the US), it’s hard to stop with just one. For example, one of the things Steve and I discussed was the possibility of using two SMADs to form the ‘eyes’ of a pseudo robot head. Armed with his trusty 3D printer, Steve created what I refer to as his ‘Owl Glasses’ display. Let’s look at an exploded view showing the main frame (orange) and one SMAD (Fig.7). If you want to create your own Owl Glasses display, Steve has kindly made the design files available. A compressed ZIP file containing these design files is available on the September 2021 page of the PE website at: https://bit. ly/3oouhbl – file CB-September21-01.zip contains the files for the main frame and updated versions of both the 29-segment and 45-segment shells. Remember that Steve’s 3D printed shells come in three parts – the front half, the back half, and the facia. The only reason for splitting the main shell into two halves is to make them easier to paint (use a white primer followed by a gloss white finish to obtain the brightest and most vivid colours). Also, observe that these shells are slightly different to the standalone versions we discussed in the previous column. Those shells had clear holes for the machine screws used to mount the displays because I like to see the screw heads on my front panels. By comparison, in the case of the shells for the Owl Glasses, the holes in the front shell are threaded (as are the blind holes in the frame) because Steve prefers a no-screw look. Also, there are no screw holes in the facias, which are held in place by small lips in the frame and aligned with an alignment key (as are the shells). In the case of the diffuser, we are employing the white plastic separator sheets you can purchase to use with file folders. (For example, these white polypropylene dividers from Toner Ink Online (https:// bit.ly/3inEODY – but of course others will do just fine). Steve created two versions of his Owl Glasses display – one with 29-segment shells and the other with 45-segment shells (Fig.8). The important thing to note here is that all four SMADs are displaying exactly the same colours. This really illustrates the difference between the larger segments in the 29-segment shells where the colours from two LEDs are diffused together, as compared to the smaller segments in the 45-segment shells where the colours are kept separate. By comparison, I decided to create two ‘robot heads’ inspired in part by WALL-E (https://youtu.be/_kslEYbMr1g – see Fig.9). The white card box in the foreground of 46 Practical Electronics | September | 2021 Fig.6. It’s a SMAD, SMAD, SMAD, SMAD world: (left) SMAD board, (right) SMAD LED and segment map. for only £11.95 each, which includes the potentiometers, which we can feed shipping in the UK (shipping outside to one of the microcontroller’s analogue the UK will be quoted separately). inputs. If we add a second board, we can Each SMAD contains 45 tricolour use the same four control pins to select LEDs (Fig.6 left). Typically, we attach one of the sixteen digital signals from the a ‘shell’ to the front of the board to potentiometers’ switches, and we can feed compartmentalise the light from the this signal to one of the microcontroller’s LEDs, where these shells can be 3D digital inputs. Thus, using only six of printed or laser-cut (see last month’s the microcontroller’s pins, we can read Cool Beans for more details). Our original the analogue and digital values from ten shells boasted 29 segments, with 13 potentiometers and associated switches. segments containing only one LED and Pretty cool, eh? 16 segments containing two LEDs (Fig.6 right). However, Steve then decided Are you SMAD? to experiment with 45-segment shells As we discussed in last month’s Cool with one LED per shell, which left us Beans (PE, August 2021), creating a fullin a bit of a pickle. On the one hand, we up 10-character 21-segment Victorian delight in the gradient effects that can be display is a bigger project than most achieved by varying the colours of the readers care to commence. Also, the LEDs forming the dual-LED segments software for the little rapscallion is more in the 29-segment shell; on the other complex than we want to discuss here. hand, we relish the stained-glass effect Our solution was to create SMAD boards, presented by the 45-segment shells. In which are available for purchase from the the end, we decided to use both. PE PCB Service (https://bit.ly/3wVUgLq) SMAD PCB (1.6mm) Back half of shell (5mm + 1.6mm) Front half of shell (5mm) Diffuser (0.1mm) Facia (1mm) Alignment key Owl Glasses frame (13.7mm) Fig.9. Two robot heads with 45-segment shells (left) and 29-segment shells (right). Fig.8. Two Owl Glasses displays with 29-segment shells (top) and 45-segment shells (bottom) (Image: Steve Manley). this image is the mockup I created as a prototype. Observe that I’ve still got to build the overhanging tops and sides for the real heads. Just to vary things up a bit, I decided to have black shells on a nickel-coloured face for one head, and nickel-coloured shells on a black face for the other. I used slotted, pan-head steel machine screws to attach the shells because it matches my ‘steampunk aesthetic’ (in the case of the black shells, I used ‘gun blue’ liquid to blacken the heads of the screws). The very first test For my very first test, I just wanted to make sure that I could light the red, green and blue channels in each of my LEDs individually (you can see my code in file CB-September21-02.txt). Remember that we are using WS2812 LEDs (a.k.a. NeoPixels), which can be daisy-chained together. In my case, I’ve also daisychained all four SMADs, thereby giving me a single string of 4 × 45 = 180 LEDs. At the top of my sketch (program) you will see the following definitions: #define NUM_NEOS_PER_SMAD 45 #define NUM_SMADS 4 Also, I define NUM_NEOS as being NUM_ NEOS_PER_SMAD multiplied by NUM_ SMADS. This means that you can easily modify this program to work with your own setup comprising one, two, or more SMADs by simply changing the value assigned to NUM_SMADS. We introduced NeoPixels in depth in an earlier Cool Beans (PE, July 2020), but it might be a good idea to briefly remind ourselves as to how these little beauties work in case you are new to the party. First, make sure you have the latest version of the Arduino Integrated Development Environment (IDE) downloaded to your Practical Electronics | September | 2021 computer from the Arduino.cc website (the current version at the time of this writing is 1.8.15). Next, make sure you have the latest version of whatever library you wish to use to control your NeoPixels. If you wish to use Adafruit’s NeoPixel library, launch the Arduino IDE, select ‘Tools -> Manage Libraries,’ search for ‘Adafruit NeoPixel,’ and install the ‘Adafruit NeoPixel’ entry (don’t be lured by the DMA and other options). Alternatively, if you prefer to use the FastLED library created by Daniel Garcia, search for ‘FastLED’ in the Arduino’s library manager. (If you already have these libraries installed, you can use the same mechanism to check to see if they need to be updated.) When you instantiate your string of NeoPixels (I named my string ‘Neos’), you specify the number of pixels in the string and the microcontroller pin you are using to control them (look at my test program for an example). The act of instantiating the string creates an array in the Arduino’s memory. This array contains three bytes for each pixel, where these bytes are used to store that pixel’s red, green and blue components specified as 8-bit integers with values from 0 to 255. Suppose we wish to change the colours associated with pixel 6 to be red = 255 (0xFF in hexadecimal), green = 128 (0x80), and blue = 66 (0x42). We can do so by specifying each channel individually using Neos.setPixelColor(6, 255, 128, 66) or Neos.setPixelColor(6, 0xFF, 0x80, 0x42). Alternatively, we can specify all three colour components as a single value using Neos.setPixelColor(6, 0xFF8042). The important thing to remember is that the setPixelColor() function doesn’t actually modify the display in the real world. All it does is to change the values in the array stored in the Arduino’s memory. It’s only when we use the Neos.show() function that all the colour values in the array are uploaded into the NeoPixel string and presented to the user. Good dates Earlier on, we posed a question as to the best way to set the date on the Victorian display. I seem to have dates on my mind, because I was just reminded of the scene from Raiders of the lost Ark when Indiana Jones throws a date into the air and his friend Sallah (on seeing the dead monkey) grabs it and says, ‘Bad dates’ (see: https:// bit.ly/2UzTgiu). Of course, we are dealing with the other kind (ie, good dates). Originally, when it came to setting the date on my Victorian display, I was thinking of the display showing things in the form YYYY/DD/MM or DD/MM/YYYY, or even MM/DD/YYYY, as we discussed earlier. But then it struck me that we have a full-up alphanumeric display capability, which means we can use the display to show, ‘YEAR=?’ followed by ‘MONTH=?’ followed by ‘DAY=?’ and – in each case – simply leave the user to enter the appropriate number and then press the OK button. Coming soon In next month’s column we will start to experiment with some of the clever effects we can achieve with our SMADs. In the meantime, I would love to see pictures should you decide to create your own robot head or any other form of SMADbased artifact (we might even feature your creation in a future column). Until then, as always, I welcome your comments, questions and suggestions. Cool bean Max Maxfield (Hawaiian shirt, on the right) is emperor of all he surveys at CliveMaxfield.com – the go-to site for the latest and greatest in technological geekdom. Comments or questions? Email Max at: max<at>CliveMaxfield.com 47