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Max’s Cool Beans By Max the Magnificent Flashing LEDs and drooling engineers – Part 18 A s usual, I have so many things bouncing around my poor old noggin that I don’t know where to start, not the least of which is that just saying the word ‘noggin’ has reminded me of Noggin the Nog (https://bit.ly/3ckKqed), which was a cult classic from the golden age of British children’s television when I was a kid in the early 1960s. Revisiting Victorians Let’s start by reminding ourselves that in my previous column (PE, July 2021) I introduced my new hobby project, which involves recreating 21-segment Victorian displays using modern tricolour LEDs. To be honest, my chum Steve Manley in the UK is doing most of the heavy lifting on this project – designing the circuit boards, for example – with me bobbing up and down like a deranged meerkat (https:// youtu.be/57jEMZ87ND8) in the background, offering helpful (some may say useless) suggestions. Steve started by creating a single-character display board 50mm wide by 64mm tall. Seven of the segments have only one tricolour LED, while the other fourteen segments each have two LEDs, resulting in 35 LEDs in all. Steve also created a 3D printed ‘shell’ that’s 10mm deep and which separates the LED board from a diffuser. Steve and I are both creating 10-character displays, which therefore employ 10 LED boards and 10 shells. Actually, this would be a perfect time for you to take a look at a video Steve posted on YouTube that shows all of this in fantastic detail: https://bit.ly/2T4sgXl The problem is that we have 35 × 10 = 350 LEDs, each requiring 24 bits of data (8-bits each for the red, green and blue channels). The Adafruit Library uses a clock rate of 800kHz, which means it takes (350 × 24) / 800,000 = 0.0105 seconds (s), or 10.5 milliseconds (ms) to upload all the data. Let’s round this up to 11ms. One point to note here is that while the Adafruit library is uploading the data to the LEDs, it’s consuming 100% of the microcontroller’s central processing unit (CPU) resources, which means the CPU cannot be doing anything else during this time. I’m reasonably confident that we are going to be performing a humongous number of calculations to implement the special effects we have in mind. If we assume that we can perform all of these calculations in 9ms, this means we have a total cycle time of 11 + 9 = 20ms. In turn, this means we have a maximum refresh rate of 1,000 / 20 = 50Hz for our display. To be honest, this is probably more than adequate for this particular application but – given a choice – we’d prefer to do better. Since we are using a Teensy 3.2 or 3.6 microcontroller, another alternative is to use PJRC’s OctoWS2811 library (https://bit.ly/3z589ZO). This library has a limited set of inbuilt functions, which means you have to do things like fading from one colour to another yourself (this is true of the Adafruit library also). However, its main claim to fame is that it Take control Another thing we discussed in my last column is the fact that, in previous projects, Steve and I have gone our own way with regard to hardware (eg, microcontrollers) and software (eg, libraries), which resulted in an inability to share our code. In order to address this problem, in the case of our Victorian displays, we decided to employ a common platform, thereby allowing us to work on the code in a collaborative manner. The first piece of this platform was the control board. Since we intend this board to be of use for future projects, we’ve added everything we can think of in a general-purpose sort of way. Our board includes a real-time clock (RTC), an audio codec with an on-board microphone so we can respond to sound, a light-dependent resistor (LDR) so we can respond to ambient light, and infrared (IR) control. It can be ‘powered’ by either a Teensy 3.2 or a Teensy 3.6 microcontroller from PJRC: https://bit.ly/3h5tifW Lucious libraries Remember that each of our 21-segment characters boasts 35 tricolour LEDs. These are WS2812 devices, which are known as ‘NeoPixels’ by the Adafruit community. One option open to us is to use the Adafruit NeoPixel library (https:// bit.ly/2T3s2zH) to control our LEDs. Personally, I love this library, but that’s probably because it’s the one I first used deep in the mists of time. 62 Fig.1. Power distribution board (Image source: Steve Manley). Practical Electronics | August | 2021 Precocious prototypes Fig.2. Prototyping board (Image source: Steve Manley).. uses the microcontroller’s on-chip direct memory access (DMA) engine to upload eight strands of LEDs simultaneously. Even better, the DMA engine runs in the background, thereby leaving the main CPU free to work on the next set of calculations. There’s even a busy() function you can call to determine if the previous upload has finished before starting a new one. But wait, there’s more, because there’s also the FastLED library (fastled.io), which is the one Steve favours. In addition to being targeted at lower-performance (8bit) microcontrollers, the FastLED library offers all sorts of tasty functions, including HSV support in addition to RGB, where HSV stands for ‘hue, saturation, and value’ (another name for ‘value’ is ‘brightness’). There are some awesome FastLED videos available that explain all of this in detail – just bounce over to YouTube and perform a search on ‘FastLED Basics.’ The really cool thing is that the FastLED library can be used in conjunction with the OctoWS2811 library. Unfortunately, we haven’t yet worked out how to set the DMA engine running in the background when using this library combo; however, we can still upload multiple strings of LEDs simultaneously. Since our Victorian displays have 10 characters, we are treating them as five 2-character pairs, and since each pair comprises 70 LEDs, this means our upload time is now reduced to (70 × 24) / 800,000 = 2.1ms, which increases our maximum possible refresh rate accordingly. Feel the power In the case of future projects employing fewer LEDs, we could decide to power those LEDs directly from the main control board. However, as we previously noted, each of our Victorian characters has 35 LEDs. These devices are of the WS2812B flavour that consume a maximum of 15mA for each RGB sub-channel, which means a total of 3 × 15 = 45mA per device. In turn, this means that if every LED in every segment was full-on white, each character would be consuming 45 × 35 = 1575mA, or around 1.6A, which equates to 16A for the full display. Eeek! Obviously, this is a worst-case scenario, but it has to be taken into account. Thus, in addition to the main control board, we also decided to create a power distribution board (Fig.1). Since we were creating this board anyway, we decided to throw on a meaty 3.3V regulator, which can be used to power things like sensors in future projects. Although we attempted to make our main control board as all-embracing as possible, your humble narrator is oftentimes a victim of scope creep because I keep on wanting to add more and more features. For example, in an earlier column (PE, January 2021), I talked about adding one of Adafruit’s BNO055-based 9-DOF (nine degrees of freedom) Fusion sensor breakout boards (BOBs) (https://bit.ly/3dP8EwU) to my 12×12 ping-pong ball array, thereby allowing me to control the ‘rolling’ of a lit pixel by detecting the tilt of the array. Well, in the case of my 10-character Victorian display, I was thinking if might be fun to add a similar capability such that tilting the display to the left could cause text to ‘slide’ in from the right, and vice versa. Thus, we also decided to create a prototyping board (Fig.2). There are several interesting things to note about this board. Let’s start with the lowhanging fruit in the form of the mounting holes, some of which are slots. A similar arrangement is seen on the main control board (PE, July 2021). This came about because Steve decided to increase the gap between adjacent characters by about 3mm, which caused him to print new 3D shells that were 1.5mm wider on each side. Thus, having these slots means that our control and prototyping boards can accommodate both types of shells. Now observe that, as opposed to having only 5V and 0V rails running horizontally across the top and bottom of the board, as would be seen on a traditional prototyping board, this board also provides 3.3V rails. Furthermore, by offsetting the vias (plated-through holes), Steve managed to Fig.3. Starting the build. Practical Electronics | August | 2021 63 Fig.4. Feast your orbs on my wiring. squeeze a trio of 5V, 3.3V, and 0V rails running across the centre of the board while still maintaining the traditional 0.3-inch separation between the vertical component signals on the upper and lower halves of the board. In fact, there are a bunch more innovative features associated with this bodacious beauty, but we have other fish to fry, as it were. All together now Before we go any further, let’s take a brief stroll through the assembly of the main section of my 10-character display, commencing with all of the bits and pieces being gathered together (Fig.3). In the middle of this image, we see the 10 shells. These were 3D printed in grey plastic. I then sprayed them with a white primer follower with gloss white, because this dramatically improves the intensity of the display. Behind the shells, we see the back sides of the 10 LED circuit boards. These are presented in pairs linked by small bridging boards that Steve created, but that he can no longer use since he increased the spacing of his characters (Ha!). In the foreground, we see a pseudo brass panel, which was cut for me by my chum Kevin, who is the owner of The Laser Hut in the UK (https://bit. ly/2RqQ1Zj). I have awesome plans for a cabinet to house my display, but we will leave that for another day. I won’t bore you with a step-by-step account of this build, save to say that the wiring took me a lot longer than I’d expected because I didn’t want to let the side down (Fig.4). As I told my wife (Gina the Gorgeous), I could have wired everything up a lot faster if I was prepared to sacrifice neatness. The problem is, deep in the mists of time, as part of his apprenticeship before moving on to research and development, Steve served in an aircraft electrician’s department. As a result, his wiring always looks awesome, and I didn’t want to be outdone. In my case, I decided to mount the control board in the middle of the display, the power distribution board on the left, and the prototyping board on the right. Have you noticed that these boards are coloured red, green, and blue, respectively? This was a little visual joke that tickled our fancy. Ideally, we would have made the power distribution board red and the control board green, but – for reasons unknown – the printed circuit board (PCB) fab Steve used would have charged a lot more to have the 2 oz copper required by the power board presented on a red substrate, so we went with the flow. I don’t know about you, but I’m really impressed with the way this all came out (Fig.5). A bit of a character There are multiple ways in which we intend to use our displays. One will be to display numerical information like the date and time. Another will be to display textual messages. In order to do this, we need to decide which groups of segments need to be illuminated in order to represent the various alphanumeric characters and punctuation symbols. In fact, there’s an incredibly useful character visualisation tool available on the internet (https://bit.ly/3wYvvyn). This is presented on two pages, which can be selected at the top. The ‘Produced’ page allows you to choose between 8-, 16-, 24-, Fig.5. The final assembly. 64 Practical Electronics | August | 2021 Fig.6. Segment map (Image source: Steve Manley). 34-, 43-, 66-, and 93-segment displays (the 8-segment is actually a 7-segment with a decimal point). By comparison, the ‘Experimental’ page allows you to choose between 6-, 21-, 23-, 50-, 52-, and 55-segment displays. I strongly recommend that you take the time to visit and play with this tool. Go to the ‘Experimental’ page and select the 21-segment option. By default, the display cycles between random characters, but if you start typing you will see the characters you type appear before you. Furthermore, if you move your mouse cursor across the display, you will see whatever segment is under the cursor light up white (if that segment is currently off) or pink (if that segment is currently on). You can click on the various segments to toggle them on and off in order to see how different combinations will appear. Come to the fore Before we proceed, let’s pause to consider our LED/segment map (Fig.6). As we see, we can think of our 21 segments as being annotated ‘A’ to ‘U’ and our LEDs as being numbered from 0 to 34. Now, ( a ) R i ng s we aren’t going to dive deep into our code here. Suffice it to say that we have definitions of which LEDs correspond to which segments and which segments correspond to which characters. For example, our letter ‘A’ is defined as comprising segments A, B, C, D, E, H, I, J, K, L, O, S, and U. Our character definitions are represented as 32-bit hexadecimal values, of which only 21 bits are used, where each of these bits corresponds to a segment, and 0 or 1 values are used to specify if that segment should be off or on, respectively. So, how are we going to actually display our characters? Suppose we wish to display white characters on a black background. The simplest approach would be to start by turning all of the segments off (black), and then setting the segments corresponding to a ‘1’ in our definition on (white). Alternatively, if we desire black text on a white background, then we could start by turning all of our segments on (white), and then clearing the segments corresponding to a ‘1’ in our definition to off (black). A more sophisticated approach – the one we are using – is to have the concept of a foreground colour, a background colour, and a mask. Let’s say that we set our background colour to black and our foreground colour to white. Our character definition acts as the mask. In the case of the segments corresponding to a 0 in our character definition, we display the background colour. By comparison, in the case of the segments corresponding to a 1 in our character definition, we display the foreground colour. Thus far, we’ve assumed static colours. Where this starts to get really clever is if we allow both our background and foreground colours to be dynamic. For example, we could present a constantly changing rainbow of colours on the segments forming our background while having the foreground colour a static white. Furthermore, each of the background segments could be the same ( b ) Verti ca l s l i ces Fig.7. Different ways of slicing and dicing the LEDs. Practical Electronics | August | 2021 ( c) H ori z onta l s l i ces rainbow colour, or we could have the rainbow rippling across the display. Slicing and dicing Once you’ve wrapped your brain around the foreground-background concept – in particular, the fact that any of the effects we are displaying are logically separated from the way in which we control the segments to represent the characters – then you will start to realise just how powerful this technique can be. This leads us to consider different ways in which we might decide to ‘slice and dice’ our LEDs. For example, we could think of them as being concentric rings (Fig.7a). In this case we could implement what Steve and I refer to as a starburst effect with different colours radiating out from the centre. Steve created an example video showing this type of effect on two adjacent characters (https://bit.ly/3fZTkjT). Now imagine displaying the date, time or text with this starburst effect applied to the background colour and the foreground colour set to white. Alternatively, imagine this effect applied to the foreground colour with the background colour being set to black. Similarly, for some effects we might want to think of the LEDs being grouped in vertical ‘slices’ (Fig.7b), while for other effects (eg, a graphic equaliser or audio spectrum analyser) we might want to consider the LEDs as being grouped in horizontal ‘slices’ (Fig.7c). Get SMAD! It was around this point that we ran into a bit of a problem. In future columns, I would love to share code examples with you, but the code for our Victorian displays is a tad too complex to show anything meaningful in this sort of setting. Also, it’s unlikely that many readers would want to invest the time and effort (and money) in building something like one of our 10-character 21-segment Victorian displays. But turn that frown upside down into a smile because we have a cunning plan. Indeed, it’s a plan so cunning that we could pin a tail on it and call it a weasel, as Blackadder would say (always remember that, while eagles may soar, weasels rarely get sucked into jet engines). What we’ve done is to create a special incarnation of our original display, where this new version is called a SMAD (Steve and Max’s Awesome Display). As you can see, this has the hint of a sniff of the look-and-feel of one of our Victorian displays, but it’s more symmetrical 65 a tempting teaser, take a look at a video of an early test that Steve performed as soon as the boards arrived back from fabrication and assembly (https:// bit.ly/3z5xCSJ). On the left we see a bare SMAD board; on the right we see a SMAD with a 29-segment 3D printed shell and Fig.8. SMAD circuit board with 45 tricolour LEDs (Image source: diffuser (Fig.9). Steve Manley). For our diffand contains 45 tricolour LEDs grouped users, we are employing the white plastic into 29 segments (Fig.8). In this case, the separator sheets you can purchase to devices we are using are of the WS2812C use with file folders, such as the white flavour that consume a maximum of polypropylene dividers from Toner Ink only 5mA for each RGB sub-channel, Online (https://bit.ly/3inEODY). If you which means a total of 3 × 5 = 15mA per look closely, in the right-hand image, you device. This means that if every LED in can see the corners of the square circuit every segment was full-on white, each board sticking out from behind the round character would be consuming only 15 shell. This explains the ‘breakaway’ holes × 45 = 675mA or around 0.7A. and slots in the corners of the board in The really exciting news is that these Fig.8. If you break these corners off, SMAD boards, which are a modest 70mm the contour of the board will match the × 70mm square, are available from the contour of the shell. PE PCB Service (https://bit.ly/3wVUgLq) As you will discover, we can create for only £11.95 each, which includes mind-boggling ‘Ooh!’ and ‘Aah!’ effects shipping in the UK (shipping outside the using a single SMAD. Now, imagine what UK will be quoted separately). Observe we can do with two. Do you remember that there are two sets of 0.1-inch pitch the WALL-E animated movie in which 3-pin pads shown in the foreground of the friendly little robot had two big this image. One set comprises 0V, 5V eyes? Well, that’s what I’m planning and Data-in (the legends are on the back on doing – creating a simple ‘head’ that of the board); the other comprises 0V, has two SMADs as eyes and then seeing 5V and Data-Out (for use if you wish to what effects I can create, like ‘blinking’ daisy-chain multiple SMADs together). or ‘looking’ left, right, up and down. Note that you’ll have to provide your Maybe using colours to reflect emotions own 3-pin headers, or you can solder like happy, sad and angry. The world is wires directly to the pads. our lobster (or oyster or crustacean of In future columns, in addition to our choice). cogitating and ruminating on our Victorian displays, we will be perusing 29 or 45? and pondering small test programs to run I must admit that I was a happy chappy on our SMAD boards. I’m thinking that, – a man with a plan (if we don’t have a as one of our experiments, we could make plan, we’re no better than arts students, as it react to sound in interesting ways. As the saying goes) – until that little scamp Fig.9. Early test: Bare SMAD (left). SMAD with shell and diffuser (right). 66 Steve threw a great big spanner into the works. The man simply cannot stop playing with his 3D printer. As we saw in Fig.8 and Fig.9, SMADs were originally conceived as being 29-segment displays with 13 small segments containing one LED each and 16 long segments containing two LEDs each. But then Steve decided to see what would happen if he created a shell that partitioned each of the longer segments into two halves, thereby creating a 45-segment display. Originally, I was not a fan of this idea because I like the subtle gradient effects that can be achieved by mixing two colours in the same segment. But then Steve created a new video and now I’m not so sure (https://bit.ly/3pqNavS). On the left we see a bare SMAD board, in the middle we see a SMAD with a 29-segment 3D-printed shell and diffuser, and on the right, we see a SMAD with a 45-segment 3D-printed shell and diffuser (Fig.10). We now tend to refer to the 29-segment and 45-segment incarnations as a ‘gradient fill’ and ‘stained glass’ shells/ SMADs, respectively. The problem is that I can’t decide which I like best. As a result, I now have to build two robot heads, one boasting a pair of gradient fill eyes and the other flaunting a brace of stained-glass eyes. For your delectation and delight, if you decide to purchase one or more SMADs and you wish to print your own 3D shells, then Steve has kindly made his DXF and STL files available to us. Compressed ZIP files containing these design files are available on the August 2021 page of the PE website at: https://bit.ly/3oouhbl – files CBAugust21-01.zip and CB-August21-02. zip contain the files for the 29-segment and 45-segment displays, respectively. If you do determine to avail yourself of these files, you’ll see that the shells come in three pieces: back, front and facia (or faceplate). Steve split the main 10mm-thick shell into the two 5mmthick front and back sub-shells in order to make them easier to spray-paint. The thin sheet of white plastic diffuser is placed between the front shell and the 1mm-thick facia. But wait, there’s more... Do you recall earlier in this column when I mentioned my chum Kevin, who is the owner of The Laser Hut? Well, on the off chance you don’t have a 3D printer, but you still want some shells for your SMAD displays, Kevin can use his lasers to cut shells out of 9mm-thick MDF, along with facias cut out of 1mm-thick black or pseudo-metallic (nickel) materials. In fact, Kevin sent me a video of the laser cutting a pseudo-nickel facia (https:// bit.ly/3cn7ucu). As I pen these words, I have four MDF shells winging their way to me – two Practical Electronics | August | 2021 Fig.10. Bare SMAD (left), 29-segment shell (middle), and 45-segment shell (right). 29-segment and two 45-segment. Each of these shells is accompanied by two faceplates, one black and one pseudonickel. I shall report further in a future column. For the moment, let me just say that Kevin has agreed to supply these little rascals to anyone who wants them (you can contact him at pe<at>thelaserhut. co.uk). One 9mm-thick MDF shell and one 1mm-thick face plate (your choice of black or pseudo-nickel) will cost £10, while two of each will cost £18. In both cases, the postage will be £1.60 in the UK (postage outside the UK will be quoted separately). GET T LATES HE T CO OF OU PY R TEACH -IN SE RIES A VAILA B NOW! LE Next time Eeek Alors! This column has certainly ‘grown in the telling.’ I’m scared to think what our illustrious editor and publisher Matt Pulzer is going to say when he sees how big it is. I only hope that the radiance of Matt’s smile will continue to lighten my life. In my next column, we will delve deeper into matters pertaining to my 10-character 21-segment Victorian display, and we will also start to create some experimental code and effects to run on our SMAD displays. Until that frabjous day (Callooh! Callay!), as always, I welcome your sage comments, insightful questions and helpful 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 Order direct from Electron Publishing PRICE £8.99 (includes P&P to UK if ordered direct from us) EE FR -ROM CD ELECTRONICS TEACH-IN 9 £8.99 FROM THE PUBLISHERS OF GET TESTING! Electronic test equipment and measuring techniques, plus eight projects to build FREE CD-ROM TWO TEACH -INs FOR THE PRICE OF ONE • Multimeters and a multimeter checker • Oscilloscopes plus a scope calibrator • AC Millivoltmeters with a range extender • Digital measurements plus a logic probe • Frequency measurements and a signal generator • Component measurements plus a semiconductor junction tester PIC n’ Mix Including Practical Digital Signal Processing PLUS... 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