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Max’s Cool Beans By Max the Magnificent Flashing LEDs and drooling engineers – Part 22 J ust a couple of days ago – as I pen these words – I received an email from a new subscriber to this illustrious magazine. The gentleman in question was querying the ‘Drooling Engineers’ portion of the title to our current series of Cool Beans columns. I replied that it originated from the fact that I’m prone to proclaim, ‘Show me a flashing LED, and I’ll show you a man drooling.’ I can only assume that the fact I’ve heard nothing since that time is because he’s still rolling on the floor laughing. Sew a button on your head You know how you sometimes start a sentence by saying ‘So...’ and then pause to gather your thoughts before proceeding. Well, many moons ago, I had a friend of the female persuasion who abhorred a conversational vacuum, and who would fill it by saying, ‘Sew a button on your head.’ I had no idea what this meant, and I used to find it extremely annoying, so... it’s ironic that I now tend to find myself doing the same thing to other people. The reason I mention this here is that I’m eager to embark on a new endeavor. Do you recall my Pedagogical and Phantasmagorical Inamorata Prognostication Engine project? It was instrumental in kicking off this Flashing LEDs series of columns in the first place (PE, March Fig.1. My ginormous variable capacitor – do you have bigger one?! 42 2020). The raison d’etre of this bodacious beauty, which currently resides in my office, is to predict the mood of my wife (Gina the Gorgeous) and inform me as to which way the wind is blowing before I set off home in the evening. Paradoxically, should Gina ever come to discover the beast’s true purpose, I won’t need it to predict her mood. Everyone who encounters the groundbreaking Prognostication Engine is enthralled. Many of my friends have told me that they could do with one themselves. In fact, I am often asked to bring it to events like local hamfests to adorn the booth of a technical company or radio society. The problem is that it’s a tad large – it stands taller than me – and is more than a little delicate, so I prefer to leave it where it is. My new machine, which we will call the Sewing Engine, will be much more mobile. It’s going to be housed in an antique sewing machine table with a cast iron base, much like the one that appears on the Olde Good Things website (https:// bit.ly/3n56Ogz). Mine is almost identical, except that I certainly didn’t pay the $250 the folks at Olde Good Things were asking for theirs because – knowing what I was looking for – my chum Carpenter Bob acquired one for a song at an auction out in the country somewhere. I’m still mulling things over in my head as to the actual implementation. One thing I do know is that I’m going to finally get to use the ginormous variable capacitor that was gifted to me a couple of years ago by my chum Paul Parry of Bad Dog Designs (https://bit.ly/3v5NMtS). This little scamp (the capacitor, not Paul) is about 30 × 30 × 30 cm (Fig.1). I’ll be removing its current wooden box base and repurposing that for something else, but – for the moment – observe the drive belt on the left. Paul removed the end stops that limited the motion of the moving part of the capacitor. This means it’s now free to continuously rotate around, which is going to look mega-impressive. I don’t like to boast (I take enormous pride in my humility), but I bet my variable capacitor is bigger than yours! Another thing I know is that the Sewing Engine is going to flaunt five humongous vacuum tubes, like those perched on top of the Prognostication Engine (the tallest of which is 13-inches from tip to tail). I acquired these tubes, which are no longer functional, for a pittance several years ago from a local electronics store that was going out of business, and I’ve been waiting for an occasion to use them ever since. In the case of the Prognostication Engine, there is a metal band around the base of each tube (for the Sewing Engine, I’ll be using cunning 3D printed bands that were designed by my chum Steve Manley). Inside each band is a strip of 30-or-so WS2812 tricolor LEDs. Way back in the mists of time, I started by lighting these LEDs with static values, but the resulting display turned out to be almost impossible to perceive in regular ambient lighting conditions. Next, I experimented with dynamic effects, such as having lit pixels chasing each other around the bands (Fig.2). The human eye is incredibly sensitive to motion, so the effect is quite startling, to the extent that the structures inside the tubes sometimes appear to be rotating in the opposite direction. To let you see what I’m waffling about, I just took a quick video in my office: https://bit.ly/3ax6EZu In addition to displaying various random sequences, I may also decide to make these LEDs respond to sound, Fig.2. Using LEDs to give old vacuum tubes a new lease of life. Practical Electronics | December | 2021 Fig.3. A cheap-and-cheerful 3-phase 12V motor controller. but that will be a story for another day and a future column. Motoring along Returning to my variable capacitor, one end of the drive belt is attached to a sprocket on a shaft that drives the capacitor, while the other end is affixed to a sprocket on a shaft driven by a motor that’s lurking in the wooden base. I vaguely remembered Paul telling me that this was a 12V motor, but that was about it, so you can only imagine my surprise when I looked inside the base to find a small gear and motor combo about 1.5 inches in diameter and 4 inches long. Actually, that wasn’t the surprise. The surprise was the fact that there were three wires coming out of the motor. ‘Ah Ha!’ I thought, ‘What we have here is a 3-phase brushless motor.’ The advantage of brushless motors is that they are extremely quiet, both physically (audibly) and electrically (in the form of electromagnetic noise). The downside is that they are a right #$%$#$ to control if you wish to build your own controller from the ground up. Fortunately, you can purchase a cheap-and-cheerful controller from eBay (https://bit.ly/2YLSLUi), so that’s what I did (Fig.3). I remembered that Paul used four of these motors to drive the drums on the front of his legendary Bombe clock (https:// bit.ly/3p0tH76), which is a replica of Alan Turing’s ‘Bombe’ that helped British Intelligence officers decipher messages coded by the German Enigma Machine during WWII. I once saw this marvelous machine in action, and you couldn’t hear a whisper from the motors. Is there a doctor in the house? One of the problems with the control board for the 3-phase motor is that it doesn’t appear to be geared up (no pun intended) to be controlled from a microcontroller. The jumper to the right of the far side of the board can be used to control the rotational direction of the motor, while the potentiometer on the lower left-hand side can be used to control its speed. If I wanted to Practical Electronics | December | 2021 Fig.4. The Dr.Duino Explorer (Image source: Guido Bonelli). control this using an Arduino Uno, for example, I’m wondering if I can use a regular digital input/output signal to replace the jumper and a resistor-capacitor-smoothed pulse-width modulated (PWM) output to replace the potentiometer. One of my ‘go-to’ boards when I’m prototyping something like this is the Dr.Duino Explorer (https://bit.ly/2YSrIat), which was created by my chum Guido Bonelli. This is an interesting board in that it can act as a shield that you plug on top of an Arduino Uno, or you can skip the Uno and plug an Arduino Nano into the Explorer, as shown in Fig.4. Instead of using a regular breadboard and fighting your way through a rat’s nest of wires, the Explorer provides most of what you need to prototype a bunch of projects, like my attempt to control my motor controller board, for example. The Explorer provides four pushbutton switches, three potentiometers, a lightdependent resistor (LDR), four red LEDs, and a bunch of current-limiting resistors. The shield also features a piezo buzzer and a stick of eight NeoPixels. Furthermore, there’s an organic LED (OLED) display in the upper right-hand corner of the board; a very handy area where you can add discrete components and integrated circuits in the bottom righthand corner; and a rather meaty voltage regulator just below the OLED display. But wait, there’s more, because in addition to a small breadboard, there are pins into which you can plug a variety of I2C-based sensors and actuators (an ultrasonic ranging sensor, not shown here, is also included). One thing I should perhaps point out is that Dr.Duino Explorer is a kit that you assemble following the step-by-step online instructions that are accompanied by gorgeous high-resolution photos. These are the most comprehensive, intuitive and user-friendly instructions I’ve ever seen, and I don’t say that lightly. of unnecessary investigation or experimentation. The later addition of, ‘but satisfaction brought it back’ indicates that the risk would lead to resurrection because of the satisfaction felt after finding out. But none of this is what I wanted to talk about. I’ve said it before, and I’ll say it again – it’s strange how disparate ideas from different sources sometimes seem to come together at the same time. A couple of weeks ago, for example, I received a rather enigmatic image of a curious cat construct from my chum Alvin in the UK (Fig.5). Alvin and I co-authored a couple of books together, including How Computers Do Math (https://amzn.to/3iYNAYH) and we like to keep each other abreast of our current projects, but this one was new to me, so I asked him to expound, explicate and elucidate. Alvin responded with a video, which is when I first realised that the eyes appear to move (https://bit.ly/3DHiMDM). Alvin went on to explain that he used the OLED displays from an Adafruit Monster Mask (https://bit.ly/3ayvLen) to implement the cat’s eyes, and that he’d augmented these displays with 40mm convex plastic lenses (https://bit. ly/3azM7mP). Alvin tells me that the displays come with software accompanied by a configuration file that allows you to customise them to look like cat, snake, or human eyes. He also picked up Feeling satisfied? The old idiom-proverb ‘Curiosity killed the cat’ is used to warn of the dangers Fig.5. An enigmatic cat (Image source: Alvin Brown). 43 P in io n R a c k Fig.6. A rack and pinion gear assembly. a blank cardboard cat mask from Hobbycraft (https://bit.ly/3AHPJOf), which he then painted himself. He says the result is approximately 6 × 6 inches in size. Seeing Alvin’s cat’s eyes move made me think of the SMAD (Steve and Max’s Awesome Display) eyes on my pseudo robot heads. As I mentioned in my previous column (PE, November 2021), Steve and I have been planning on making the SMADs appear to look to the left, right, up and down by activating different groups of pixels. I was happily cogitating and ruminating on this when Alvin sent me one final email saying that he’s thinking about future enhancements, including adding a sensor to detect motion and a servo to turn the head towards the detected object. I’d no sooner started to mull over this new piece of intelligence when, much to my surprise... Robots rising ...I received a call from our illustrious publisher here at PE. Yes, the person on the other end of the phone was none other than the man, the myth, the legend (in his own extended lunchtime), Matt Pulzer (cue fanfare of sarrusophones). I’m not sure if he’d been reading (what I laughingly call) my mind, but Matt said he’d been thinking (I manfully managed to choke back a response) that it would be cool to add some form of motion to my robot heads. In addition to being able to look left, right, up, and down, Matt even suggested the possibility of using some form of linear actuator such as a solenoid or rack-and-pinion assembly to give the SMAD eyes the ability to ‘pop out’ (move forward and backward). Just to refresh our minds, a solenoidbased linear actuator involves a wire wrapped around a ferromagnetic core. If current is passed through the wire, the core will act like a magnet with north and south poles. The clever part is if the core is only partially inserted into the coil, in which case activating the current will cause the core (officially called the ‘plunger,’ in this case) to be pulled into the coil. This motion can be used to pull or push a load, like our SMAD eyes, for example. When the current is removed from the wire, a spring can be used to return the actuator to its initial position. By comparison, a rack and pinion assembly can be used to convert the rotary motion of a motor into a corresponding linear action. The way this typically works is that the high-speed, low-torque rotation of the motor is first converted into a lower-speed, higher-torque rotation by means of a gear train. A special gear wheel called the ‘pinion’ is attached to the shaft coming out of the gear train, and the teeth on the pinion engage with teeth on the rack (Fig.6). Now, I’m certainly not going to tell Matt that we aren’t going to do this (that is, having the eyes move forward and backward). Just to be clear, we aren’t going to do this, it’s just that I’m not going to tell Matt – it’s just our little secret. However, we are going to give our SMAD eyes the ability to move left, right, up, and down. Pan-and-tilt and curved orbs There are several parts to this puzzle. For example, in order to perform some short-term cheap-and-cheerful experiments, I just purchased two pan-and-tilt mechanisms from Adafruit (https://bit. Fig.7. Pan-and-tilt mechanism (Image source: Adafruit). 44 ly/3lIjQB1). Each of these little beauties comes fully assembled and equipped with two SG-90 or SG-92 micro servos that allow the assembly to pan approximately 180° from side-to-side and tilt around 150° forwards and backwards (Fig.7). We’ll discuss the differences between things like servos (analogue and digital) and stepper motors in next month’s column. Also, at that time, we will be considering some rather cool 4-axis joysticks that we can use to control our panand-tilt mechanisms. Returning to my existing pseudo robot heads, you may remember that the SMADs are used in conjunction with 3D-printed shells. These shells, which are 10mm thick, divide the displays into segments (we use 29-segment and 45-segment shells depending on the effect we’re trying to achieve). In front of each shell, we have a thin layer of diffuser material (we’re using the white plastic divider sheets you find in file folders). In front of the diffuser, we have a 1mm-thick facia (face plate). I talked about all of this with my SMAD collaborator Steve Manley. The first thing Steve thought of was that we should create new curved facias for our SMADs to make them look a little more eye-like (Fig.8). From left to right this image shows the back shell, front shell, diffuser and curved facia. The only reason for splitting the main shell into two 5mm slices is to make it easier to use a spray to paint the inside faces of the segments white (this dramatically increases the brightness of the ensuing display). Although the curve of the facia is quite subtle (only 5 mm at the center), the result is rather startling. Apart from anything else, the fact that the diffuser is located behind the facia gives the segments a 3D effect all of their own (Fig.9). Don’t forget that, should you wish to join in the fun and frivolity, then SMADs are available for purchase from the PE PCB Service (https://bit.ly/3wVUgLq) for the remarkably low price of only Fig.8. Exploded view of a 45-segment shell with curved facia (Image source: Steve Manley). Practical Electronics | December | 2021 companies will be bringing out VL53L5CX-based breakout boards (BOBs) in the not-so-distant future. These BOBs will, of course, be accompanied by training materials and example sketches (programs). -.-- .- -.-- / ... -- .- -.. -.-.-- Fig.9. The new curved facias give the segments an interesting ‘depth’ (Image source: Steve Manley). £11.95 each, which includes shipping in the UK (shipping outside the UK will be quoted separately). Also, as usual, Steve has very kindly made the 3D print files for this new version of the shells available for anyone who wants to print their own: download file CB-Dec21-01.zip from the December 2021 page of the PE website at: https://bit.ly/3oouhbl A pain in the neck! Unfortunately, I fear I’ve unleashed a monster – Steve has leapt into this project with gusto and abandon. In addition to having eyes that can move from side-to-side and up-and-down, Steve wants to extend these capabilities to the entire robot head. Steve’s already started work on his eyes. I have to say that the solution he has come up with is something I’ve never seen before and that I would not have thought of myself in a million years. Suffice it to say that Steve’s solution puts my simple pan-and-tilt mechanisms to shame. Every time we chat on FaceTime, Steve’s 3D printer is churning away in the background as he keeps on refining his design. I cannot wait to share all of this with you in future columns. Sense something strange? Earlier, I mentioned that one of the ways in which we can control the motion of our SMAD eyes and robot heads is by means of some rather cool 4-axis joysticks that we’ll be discussing in my next column. Another possibility will be to equip our robot heads with some way to sense what’s going on around them and to respond accordingly. Well, by some strange quirk of fate, I was just playing with a brand new VL53L5CX Time-ofFlight 8×8 Multizone Ranging Sensor from STMicroelectronics. This little beauty is only 6.4 × 3.0 × 1.5 mm, which makes it significantly smaller than the size of a Jellybean (Fig.10). The smaller aperture on the left houses a 940nm invisible light vertical cavity surface emitting laser (VCSEL) and integrated analogue driver. By means of an integrated lens, the laser light spreads out in a three-dimensional 45-degree cone. The larger aperture on the right holds an 8×8 receiving array of single photon avalanche diodes (SPADs) that detect the laser light reflected from objects up to 4m away. The ‘washboard’ structure in the middle is used to mitigate any laser light that’s reflected if you add a glass or plastic cover on top of the device. Also in the package is a low-power microcontroller that processes all of the data and presents it on demand to a host processor via an I2C bus. I had a lot of fun playing with this in my office. In fact, I even took a video (https://bit.ly/3mGOSIA). The reason I mention this here is that I can easily envisage using one of these sensors to detect the presence of people, monitor their movements, and cause our robot heads and eyes to track them as they move around the room. Of particular interest is that the folks at STMicroelectronics tell me that they are working with Adafruit and SparkFun, and that both of these A K B C D G Fig.10. VL53L5CX Time-of-Flight 8×8 Multizone Ranging Sensor (Image source: STMicroelectronics). Practical Electronics | December | 2021 E M N O F Q H J I L R S T Of course there’s a reason The reason I mention all of this here is that I recently received an email from a member of the PE community who we will call Simon (because that’s his name). In his message, Simon spake thus: ‘Hi Max, your column in October’s PE couldn’t have been timed better. I had in mind a little Arduino project to implement a Morse code trainer and I spent some time 1 U 2 V 3 W 4 X Y P In 1837, the British physicist and inventor Sir Charles Wheatstone and the British electrical engineer Sir William Fothergill Cooke invented the first British electric telegraph. This instrument made use of five wires, each of which was used to drive a pointer at the receiver to indicate different letters. Sir Charles was a busy man. For example, among many other things, he took the time to invent the concertina in 1829. I sometimes wonder if Sir Charles invented the concertina because he didn’t have many friends, or if he ended up with few friends because he invented the concertina. Also, in 1837, the American inventor Samuel Finley Breese Morse developed the first American telegraph. This was based on simple patterns of ‘dots’ and ‘dashes’ (or ‘dits and ‘dahs’), which we now call Morse code (Fig.11), being transmitted over a single wire. Morse’s system was eventually adopted as the standard technique because it was easier to construct and more reliable than its British counterpart. Different people can key Morse code at different numbers of words per minute (WPM). However, we can standardise things, because if we say that the length of a dot is one unit of time, then a dash is three units, the space between two parts of the same letter is one unit, the space between letters is three units, and the space between words is seven units. You can experiment with a translator here: https://morsecode.world 5 6 Z 7 ? , 8 ! . 9 0 Fig.11. International Morse code. 45 pondering how I should format the data in an array. I had come to the conclusion that it would be better to start the data array just as you did with the SMAD: declaring the length of data in each row first (see below). I felt somewhat vindicated and relieved that I was on the same track (as it were) when I read your column, so a *big thumbs up* to you!’ Simon went on to say that he had used two #define statements as follows, noting that ‘the reason for these values is because a ‘dah’ is three times the length of time of a ‘dit’ and I use them as the timing structure’: #define dit 1 #define dah 3 Based on this, Simon defined his Morse code trainer array as follows: uint8_t MorseAlphabet [26][5] = { {2, dit, dah}, // a {4, dah, dit, dit, dit}, // b {4, dah, dit, dah, dit,}, // c {4, dah, dit, dit,}, // d {1, dit}, // e etc.... we just discussed), but I took a different tack, as is my wont. For example, my program commences with two definitions as follows: #define WPM 15 #define UNIT_DELAY 1200 My unit delay is for one time unit in milliseconds assuming a transmission rate of 1 WPM. All of the other delay values are calculated as a function of this and the WPM value. Thus, assuming a transmission rate of 15 words per minute, we end up with one unit (a dot) being 1,200 / 15 = 80 milliseconds. I also defined my Morse code dots-and-dashes data array in a different way to Simon, as follows: char *DnD[] = { ".-", // "-...", // "-.-.", // "-..", // ".", // etc. This is something we haven’t discussed before. In this context, the asterisk * character declares our DnD variable to be a Well, I simply couldn’t help myself. I decided to create a little program to make my two existing pseudo robot heads have a conversation in Morse code. I’m not sure how Simon implemented his program (apart from the snippets GET T LATES HE T CO OF OU PY R TEACH -IN SE RIES AVAIL AB NOW! LE 0 = A 1 = B 2 = C 3 = D 4 = E pointer. Further, since DnD is an array of type char, this means that *DnD is a pointer to an array of strings. To be honest, explaining the way this works would take longer than we have time for here. The thing is, pointers allow us to do a whole host of cool things. If you want to know more about these little rascals, then there’s a wonderful book called Understanding and Using C Pointers by Richard Reese, see: https://amzn.to/3ASgYWI In the meantime, you can peruse and ponder my program by downloading the code (file CB-Dec21-02.txt) from the December 2021 page of the PE website at: https://bit.ly/3oouhbl Finally, for your delectation and delight, I just took a video of all this taking place – see: https://youtu.be/FmQf1q8dlFQ Next time In my next column we will look at some more SMAD display effects. We will also create some simple programs that allow us to use our 4-axis joysticks to control the servos on the pan-and-tit mechanisms, thereby causing our SMAD eyes to move around in interesting ways. 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 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... YOUR GUIDE TO THE BBC MICROBIT Teach-In 9 Teach-In 9 – Get Testing! 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