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Make it with Micromite Phil Boyce – hands on with the mighty PIC-powered, BASIC microcontroller Part 13: Controlling RGB LEDs and building a Mood Light which in turn is connected to (and drives) the red, green, and blue LEDs. Smart RGB LEDs typically have a serialcommunication link to the outside world to receive appropriate data to control the overall colour and brightness of the LED. Smart RGB LEDs are usually, but not always, packaged as a surfacemount device (SMD, see Fig.2b). Types of smart RGB LEDs that you have possibly heard of include the WS28xx, NeoPixel, DotStar and APA102. Fig.1. The Micromite Mood Light has many features and is controlled via an IR remote. It is shown here inside a modified Ikea FADO table lampshade. O ver the last couple of months we have explored serial data communication techniques. This included writing code to interpret key presses from a capacitive keypad, and also how to use bit-banging to display characters on an LED matrix. This month, we will show you how to use MMBASIC’s SPI commands to perform the function of bit-banging, and we’ll use this method to control RGB LEDs. Once we have learnt how easy it is to set the colour and brightness of an LED, we will put this knowledge into practice and build a new mini-project – a fully featured, IR-controlled Mood Light (see Fig.1). Colourful LEDs adjusting the voltage, and hence the current supplied to each of the three LEDs, the human eye is tricked into seeing a solid colour. This is exactly the technique used in colour TV for illuminating each individual RGB pixel on the screen. There are many different RGB LEDs available today, but they typically fall into one of two main types: 1. Standard 4-pin RGB LED – these have a red, green, and blue pin connected to the ‘outside world’, along with a common pin (see Fig.2a). By applying various voltages directly to the RGB pins, the LED emits a range of colours. 2. Smart RGB LED – these integrate a controller chip inside their package, A nice analogy is that the ‘standard’ type can be considered as an analogue LED (requiring voltages), and the ‘smart’ type viewed as a digital LED (requiring data). We will be using the smart digital type in our discussions this month, and use several to build the Mood Light. A useful point to understand is that a smart RGB LED (which is based on a serial communication link) includes four pins: Clk In, Data In, Clk Out and Data Out. This allows multiple smart LEDs to be ‘daisy-chained’ (the output of one feeding into the input of the next) to create a string of LEDs, while retaining the ability to individually control each LED in the string (see Fig.3). The Blinkt! module From the many RGB LEDs and modules available to choose from, we’ve selected RGB LEDs differ from normal LEDs – they can to create virtually any colour by mixing the appropriate amount of red, green, and blue light. They are able to do this because an RGB LED (as its name implies) contains a red LED, a green LED and a blue LED. These three LEDs are positioned very closely to each other inside a single package. By Micromite code The code in this article is available for download from the PE website. 66 Fig.2. a) (left) Typical through-hole 4-pin RGB LED and b) (right) Smart RGB LED – here, two views of a single APA102 SMD package. Practical Electronics | February | 2020 S D I S D O C K I C K O G N D V C C L E D 1 D A T A C L O C K V C C L E D 2 S D I C K I S D O C K O G N D V C C D a ta in p u t C l o ck i n p u t D a ta o u tp u t C l o ck o u t p u t 0 V + 5 V L E D 3 IC 1 T S O P I R r e ce L E D 8 16 Fig.3. Smart RGB LEDs can be cascaded to create a string (pinout shown here is for the APA102). the Blinkt!, manufactured by Pimoroni. It is one of the lowest-cost smart RGB LED modules available, and it comprises of not one, but eight ultra bright, and individually controllable APA102 LEDs (connected together as shown in Fig.3). The Blinkt! is actually designed to be plugged directly into a Raspberry Pi’s 40-way GPIO connector. However, as with any Raspberry Pi add-on (or any Arduino shield), there is nothing preventing us from connecting it to a Micromite. Even though the Blinkt! has a 40-way female socket, only four pins are used; two for 5V power (5V/0V), and two for the synchronous serial link (Clock and Data) – see Fig.4. So we need just four wires to connect the Blinkt! to the Micromite’s Development Module, as shown in the schematic in Fig.5. Also shown are the connections to the IR receiver that we will use later for the Mood Light. However, before we begin writing any code, we first need to understand what data the APA requires to function. L E D ( t o p ) vi e w D A T A 3 5 V 3 9 8 9 8 3 0 V 4 0 - w a y so cke 2 t ( b o t t o m ) vi e w Fig.4. The Blinkt! is a low-cost Raspberry Pi module containing eight ultra-bright APA102 RGB LEDs. Each RGB LED can individually be set to any colour and brightness via the single twowire serial interface. Practical Electronics | February | 2020 We’ll now discuss how to set all eight LEDs on the Blinkt! to full red intensity, and at maximum LED brightness. Referring to Fig.6, you will see that the bytes we need to send are: 0V 3 2 (START frame [4 bytes]) 0,0,0,0 (LED 1 frame [4 bytes]) 255 (the 8-bits: 111 11111), 0 (no blue), 0 (no green), 255 (full red intensity) (LED 2 frame [4 bytes]) 255,0,0,255 (LED 3 frame [4 bytes]) 255,0,0,255 (LED 4 frame [4 bytes]) 255,0,0,255 (LED 5 frame [4 bytes]) 255,0,0,255 (LED 6 frame [4 bytes]) 255,0,0,255 (LED 7 frame [4 bytes]) 255,0,0,255 (LED 8 frame [4 bytes]) 255,0,0,255 (END frame [4+1 bytes]) 0,0,0,0,0 The APA102 data format From the APA102 datasheet (http://bit. ly/pe-feb20-APA) we can summarise the following requirements to set the overall brightness of the smart RGB LED, as well as the red, green and blue colour intensities: 1. Send 32 zeroes (0) for the ‘start-ofmessage’ frame 2. Send 4-byte LED frame (data for brightness, and the RGB intensities): n byte 1: 111xxxxx where xxxxx = brightness value between 0 (off) and 31 (max) n byte 2: B value between 0 (blue intensity off) and 255 (max blue intensity) n byte 3: G value (0 to 255) n byte 4: R value (0 to 255) 3. Repeat step 2 for each LED in the strip (eight times for the Blinkt!) 4. 32 zeroes (0) to begin the ‘end-ofmessage’ frame 5. Send an additional eight zeroes (0) to complete the ‘end-of-message’ frame (for 8 LEDs). S T A R T fra m e 3 2 b its (4 b y te s ) L E D fra m e Bit-banging with the SPI command Last month we sent data to the 8×8 LED matrix module by bit-banging it with raw code. In summary, the Data signal was set as required to either a high (1), or a low (0) logic level, and then the Clock signal was pulsed to load the data bit into the LED matrix driver chip. This was repeated for each bit sent. In last months code we used SUB MAXwrite(value) to bit-bang a 16-bit value. We could modify SUB MAXwrite(value) to clock out 8 bits (instead of 16 bits), and then call it D a ta fo r L E D E n d fra m e s tr in g 00000000 00000000 00000000 00000000 8 b its 8 b its 8 b its 8 b its B lu e bbbbbbbb G re e n gggggggg R e d rrrrrrrr 8 b its 8 b its 8 b its 00000000 00000000 00000000 00000000 00000000 8 b its 8 b its 8 b its 8 b its 8 b its B r ig h tn e s s L E D 111 xxxxx fra m e 3 2 b its ( 4 b y te s ) 3 b its 5 b its E N D fra m e 3 2 + 8 b its So if we send the above 41 bytes to the Blinkt!, then we will see all LEDs set to red at full intensity (‘redness’), and at maximum brightness. We will demonstrate this shortly, but first we’ll discuss how to send this data to the Blinkt! 32*0 LED1 LED2 LED3 LED4 –––– LED8 (32+8)*0 S ta rt fra m e 25 Seeing red! Fig.5. The Micromite Mood Light requires just three components: an IR remote control and receiver, and the Blinkt! module – (plus some Micromite code!). The connections to the Blinkt! and the IR receiver are shown here. S D I C L O C K r 5V 25 (5 V ) G N D i ve The above is represented diagrammatically in Fig.6. If you look closely, you will see that we need to send multiple 8-bit chunks of data (multiple bytes). Let’s look at this in more details. Fig.6. The serial-data format required to control a string of APA102 RGB LEDs. 67 41 times, passing each byte shown above, one at a time, in the correct sequence. However, all this can be greatly simplified by replacing the SUB code with a single SPI command, which in effect automates the bit-banging for us. The Micromite has three pins dedicated to SPI: n Pin 25 SPI Clock n Pin 3 SPI Data Out n Pin 14 SPI Data In (not used here) To use the SPI pins, they first need to be configured at the start of our code with the single command: SPI OPEN speed, mode, bits. Please refer to the User Manual (geoffg.net/Micromite.html – see Appendix D) for detailed information regarding the SPI parameters. In the limited space here we will define the exact line of code we need to use to configure the SPI pins: SPI OPEN 1000000,0,8 (the 8 refers to 8 bits at a time; ie, one byte at a time). Once the SPI pins have been configured, we can send bytes of data with the following single command: SPI WRITE nbr, data1, data2,... where nbr represents the number of data-bytes we are sending, and dataX are the individual bytes. Using the above information we can begin to write some simple test code. First, make the four connections between the Blinkt! and the Micromite, as shown in Fig.5 (there is no need to connect the IR receiver just yet). Next, enter the following six lines of code (remember to save any existing program code in the Micromite, should you need to!). SPI OPEN 1000000,0,8 SPI WRITE 4, 0,0,0,0 FOR i = 1 to 8 SPI WRITE 4, &b11111111,0,0,255 NEXT i SPI WRITE 5, 0,0,0,0,0 On running the code you should see the Blinkt! glow bright red. If not, check the four connections are made correctly, as shown in Fig.5, and also check your code is typed exactly as shown above. To ensure you fully understand what is going on, here is an explanation of each line of code: Line 1 Configures the SPI pins at a clock speed of 1MHz, and with 8 bits per data element Line 2 Sends the start-of-message frame (four bytes of 00000000) Line 3 Forms a loop that is repeated eight times (once for each LED) Line 4 Sets the 5-bit LED brightness to a maximum, and red intensity to full Line 5 Repeats Line 4 eight times 68 Line 6 Sends the end-of-message frame (five bytes of 00000000) Changing colour and brightness Assuming you have a glowing red Blinkt!, we can now explore how to change the colour, and brightness, of the LEDs. Have a go at each of the following tasks; each will require a change to Line 4 (apart from the final task): 1. Reduce the LED brightness (hint: use &b111xxxxx where xxxxx is replaced with a 5-bit binary value such as &b11100001). Note: a brightness value of 0 (ie, &b11100000) will turn the LED off 2. Change the LED colour from red to green, and set at full brightness again (remember that Line 4 sends four bytes representing: &b111(5-bit brightness), blue intensity, green intensity, red intensity) 3. For completeness, change the LED colour to blue 4. Now create a colour based on a mix of the RGB values – start with yellow, cyan, or magenta (hint: set any combination of two out of the three RGB intensities to 255) 5. Set colour to white (hint: requires all three RGB intensities) 6. Set to a colour of your own choice such as light purple (hint: you may want to use an online colour selector tool; eg, www.rgbtool.com 7. Finally, set the eight LEDs from left to right as: red, green, blue, red, green, blue, red, green (hint: comment out lines 3 and 5 to remove the loop, then add seven lines identical to Line 4 – one for each LED. Then set the first, fourth and seventh line to red, the second, fifth, and eighth to green, and the third and sixth to blue) The above tasks will give you a clear understanding of using the SPI command to easily control RGB LEDs. Now let’s put our learning into practice by building a fully featured Mood Light, complete with an IR remote control to change colours and functionality. The Micromite Mood Light Having already connected the Blinkt! module to the Micromite (via the Development Module), all we need to do to create the Mood Light is add an IR receiver. Make the three connections as shown in Fig.5 and then download the file MKC_MoodLight.txt from the February 2020 page of the PE website. Load the program into your Micromite, and before you run it, take a quick look at the program code. I want to draw your attention to the SUB IR_Int (at the bottom of the program), which is called whenever the IR receiver detects an IR signal. On pressing a button on the 44-key IR transmitter, the variable KeyCode will be set, and its value immediately passed to SUB IR_Int (refer to Fig.7 to see the unique KeyCode value returned for each button). The main function of SUB IR_Int is to check which button is pressed (with SELECT CASE KeyCode) and to then alter the appropriate program variable(s) accordingly. Any change to any variable(s) is then immediately picked up in the main program, which will result in the required visual change to the Blinkt! LEDs. Now run the program and have a play. Below is a summary of the Mood Light’s features, and opposite a useful reference table of the operations of each of the IR transmitter buttons. Mood Light features n Three modes: static (on), fade (up/ down) and flash (on/off) n Quick set a colour: red, green, blue, white, orange, pink, magenta, yellow n Fine tune to any custom colour n Store/recall three custom colours n Adjust overall brightness n Adjust fading/flashing speed n Switch power on/off Please feel free to add and/or change the functionality to suit your own needs! Now that you have the code and electronics working, it can be finished off by placing the Blinkt! module in an appropriate housing. You will see that the LEDs are very bright, and the ideal thing to do is add a diffuser of some kind. This can be as simple as a piece of white paper, or if you want something a little more permanent, then grab yourself an Ikea 58 186 130 2 26 154 162 34 42 170 146 18 10 138 178 50 56 184 120 248 24 152 88 216 40 168 104 232 8 136 72 200 48 176 112 240 16 144 80 208 32 160 96 224 Fig.7. The 44-key IR remote control used to control the Mood Light. Shown on the right are the KeyCode numbers for each button, as used in the IR interrupt to determine which key has been pressed. Practical Electronics | February | 2020 IR (infrared) remote control button operations n Increase brightness: when in static mode, each press increases the brightness variable up to a maximum value of 31 n Decrease brightness: when in static mode, each press decreases the brightness variable down to a minimum value of 1 n Play/pause: when in static mode, toggles between minimum and maximum brightness n Power: toggles between on and off (sets brightness variable to 0 to turn off) n R: immediately switch colour variables to: rr = 255, gg = 0, bb = 0 n G: immediately switch colour variables to: rr = 0, gg = 255, bb = 0 n B: immediately switch colour variables to: rr = 0, gg = 0, bb = 255 n W: immediately switch colour variables to: rr = 255, gg = 255, bb = 255 n Coloured buttons: set appropriate values for colour variables: rr, gg, and bb n Increase red: increases the value of the red (rr) variable by 5 (up to a maximum value of 255) n Decrease red: decreases the value of the red (rr) variable by 5 (down to a minimum value of 0) n Increase green: increases the value of the green (gg) variable by 5 (up to a maximum value of 255) n Decrease green: decreases the value of the green (gg) variable by 5 (down to a minimum value of 0) n Increase blue: increases the value of the blue (bb) variable by 5 (up to a maximum value of 255) n Decrease blue: decreases the value of the blue (bb) variable by 5 (down to a minimum value of 0) n Quick: increases the speed variable n Slow: decreases the speed variable down to a minimum value of 0 n DIY1: recalls the three stored custom RGB values for custom colour 1 and loads them into variables rr, gg, and bb n DIY2/DIY3: as DIY1 (but for recalling the second or third stored custom colour) n DIY4: stores the current rr, bb, and gg variable values into custom colour 1 memory (ie, into DIY1) n DIY5/DIY6: as DIY4 (stores into either the second (DIY2), or third (DIY3) custom colour memory n AUTO: not used n FLASH: select flash mode n JUMP3/JUMP7: select static mode n FADE3/FADE7: select fade mode. FADO table lamp (around £15) and place the ‘globe’ part over the Blinkt! module. This makes for a very professional looking end product, as can be seen see Fig.1. Final thoughts for the Mood Light This mini project has resulted in a practical gadget that you may want to keep using. To avoid tying up your MKC and DM, you could replicate the simple Micromite Mood Light circuit onto a Micromite Mood Light kit A kit of parts to make the Mood Light is available from micromite.org – it contains a Blinkt! module, 44-key IR remote and IR receiver, as featured in this month’s article. Practical Electronics | February | 2020 Fig.8. The Explore28 module – an SMD version of the MKC/DM – is ideal for building a standalone Mood Light. It is available fully assembled from micromite.org (shown here actual size in the lower two photos). piece of stripboard. All you need is a 28-pin PIC (loaded with the Mood Light program), a 5V PSU, a 3.3V voltage regulator, and a tantulum capacitor with a value between 10µF and 47µF (refer to the Micromite User Manual – Quick Start Tutorial, Basic Circuit, for connections). Add the IR receiver to pin 16 (and 5V power), and the Blinkt! to 5V power, and to pins 3 and 25 as shown in Fig.5. This will totally free up you MKC and DM ready for next month’s article. An alternative to building a dedicated Micromite Mood Light circuit is to consider using a Micromite Explore 28 module instead. This is effectively a complete MKC and DM preassembled onto a single, compact PCB measuring just 40mm × 20mm (see Fig.8). This tiny size is achievable because all parts are SMD. All I/O (and power) pins are brought out onto two rows of 0.1-inch header pins, making it easy to mount onto a scrap piece of strip-board and allowing you to add the Blinkt! and IR receiver. If you need any help with any of this then simply drop me an email outlining what you need to know. Next month Whenever you work through the practical topics covered in this series, or indeed whenever you use your Micromite to work on any of your own projects, you first have to position your MKC/ DM close to your computer in order to connect them together with a USB lead. Next, you launch your preferred terminal application, point it to the relevant virtual COM port, and then you’re able to interact with your ‘tethered’ Micromite. This is something that has hopefully become second nature to you. Now imagine that you have a Micromite positioned somewhere remotely in your house; possibly in a hard-to-access position such as in the loft. Wouldn’t it be fantastic to be able to work from your usual location, and yet somehow connect your computer to the ‘remotely located’ Micromite without having to relocate it? This would then allow you to interact with an un-tethered Micromite as if it were positioned right next to you (something we will eventually need for our future robot buggy project). Next month, we’ll show you how to achieve wireless (untethered) interaction with a remote Questions? Please email Phil at: Micromite by using contactus<at>micromite.org a low-cost Bluetooth module. 69