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By Geoff Graham The Micromite Explore-28 http://geoffg.net The 28-pin Micromite has been used in many of our projects, and with good reason. It is a low-cost, powerful microcontroller which allows you to create advanced devices with minimal effort. Now the Explore-28 will make your life even easier. It’s a small plug-in module with the same powerful PIC plus a USB socket for comms and programming, giving you everything you need to get started with the Micromite in one handy package. T he Micromite is a high • A PIC32 programmer, so that you can Graeme Rixon and Robert Rozee. It update the BASIC interpreter when- can be purchased as a kit of parts or as performance 32-bit microcontrolever a new version is released. a completely assembled module from ler which can be programmed in a • A power supply with a 4-16V input micromite.org or Graeme’s website – see friendly BASIC programming language. range and the ability to supply up to the last page of this article for details. It has a lot of built-in capabilities, 150mA at 3.3V (plus 5V, when powGraeme Rixon also offers a full conincluding a variety of communications ered from USB) for external circuitry. struction pack, which you can downprotocols (I2C, SPI, serial...), the ability to easily interface to many devices This means that if you purchase a pre- load from his website. This includes the (LCD screens, GPS modules, tempera- assembled Explore-28 module, you can PCB Gerber files, parts list and firmware. So, you can get your own PCBs made ture sensors...). And it’s really easy to immediately start experimenting with it. You do not need to source the mi- and build your Explore-28 modules learn how to use it. To start with the Micromite, you just crocontroller, program the firmware or from scratch if you wish. need a programmed chip, which you setup a breadboard. It is a fully assemConnections bled and ready-to-go package. can then plug into a breadboard. It is interesting to compare the Ex- The Explore-28 has the same ‘form facThis is not hard to do, but there is a bit of fiddling about to be done before plore-28 to the Commodore 64 from tor’ as the Arduino Nano, which means you can start programming the chip. 1982, which also came with a built-in that breakout boards designed for the Many readers would prefer a pre-as- BASIC interpreter and was the most Nano will suit the Explore-28. But the sembled module that can be immedi- popular computer in the 1980s. Many two are quite different in a programmillions were sold worldwide, for ming sense; the Micromite is vastly ately put to use. more powerful and is programmed in That is the essence of the Explore-28. around US $600 each. The Explore-28 is fifty times faster, BASIC, not C/C++. You can plug it into a USB port on your The pin-out of the Explore-28 is laptop and in a few minutes, have a sim- with much more memory and costs about US $20. While they clearly have shown in Fig.1. Essentially, it mimics ple program up and running. For readers who read the short in- different end uses, this still illustrates the pins on the 28-pin DIP version of troductory series Meet the Mighty Mi- how far modern semiconductor tech- the Micromite, except pin 20 which is not present. The module also includes cromite (February to April 2017) and nology has progressed. The Explore-28 printed circuit board two extra pins at the bottom, labelled now follow the Make it with Micromite series (from February 2019), the and concept was developed by two Mi- +5V, which can be used to feed power Explore-28 combines the 28-pin Mi- cromite enthusiasts in New Zealand: in or out. cromite Mk2 with the Microbridge interface (May 2018). Another way to think about it is Explore-28 features that it is a bit like the Micromite LCD • Complete microcontroller module with USB interface and power supply Backpack V2 (May 2018) but without the LCD, and in a much smaller • Programmed in BASIC, with 60KB program space and 50KB RAM for variables package. • 19 I/O pins with 10 capable of being used as analogue inputs The whole module is only a little • Supports communications protocols including async serial, I2C, SPI and Dallas OneWire bit larger than a 28-pin DIL IC package but it packs a lot of hardware, • Support for special devices such as temperature sensors, keypads, IR remote controls including: • Full support for touch-sensitive LCD panels up to 3.6-inch (9.2cm) diagonal • A 28-pin Micromite pre-programmed with the latest MMBa• Embedded controller features such as sleep, control over clock speed and watchdog timer sic interpreter. • Built-in PIC32 programmer for updating the firmware • A USB-to-serial interface, which • Runs from 4-16V <at> 50mA allows you to plug the Explore-28 into your computer and immedi• Compact size: 40mm long, 19mm wide and 8mm tall (without header pins) ately start programming. 24 Practical Electronics | September | 2020 Fig.1: the Explore-28 has 19 I/O pins, with 10 that can be used as analogue inputs. Other connections include a 3.3V output, ground and two pins which can be a 5V output or external power input (4-16V). ANA means analogue I/O capable, DIG means digital. The other notations refer to the special capabilities of each pin – see the Micromite User Manual for a full description. When the Explore-28 is plugged into a USB port, it will power itself from the USB 5V supply, and that voltage appears on the +5V pins. This is useful if you want to power some other devices from 5V. You can also power the Explore-28 by connecting an external power source to either of the 5V pins. The input can range from 4V to 16V. For example, you could power the Explore-28 from a 12V battery. But note that if you are using an external power source, you cannot plug the Explore-28 into your computer’s USB port at the same time. The two power supplies will conflict and possibly damage your USB port or computer. Second, if you are powering the Explore-28 from a car battery, you will need to include extra circuitry to protect it from the excessive voltage spikes that can be found in an automotive electrical system. Fig.2: when the Explore-28 is plugged into a Windows computer, it is allocated a virtual serial port number by the operating system. You can check what COM number was allocated by going into Device Manager and looking for a new device listed under Serial Ports (it is COM5 in this example). Fig.3: when you have connected to the virtual serial port created by the Explore-28, you will see the MMBasic command prompt (‘>’), as shown here. At this point, you can try out commands, set options, enter programs and run them. Practical Electronics | September | 2020 The Micromite chip itself requires a 3.3V supply, and this is provided by the onboard regulator. This voltage is made available on pin 13 so that you can power external components that require 3.3V. Up to 150mA can be drawn from this pin; however, you will need to make sure that this does not cause the regulator to overheat and shut down (particularly with high input voltages). USB/serial interface The Explore-28 includes a PIC16F1455 microcontroller, which is programmed to act as both a USB-toserial interface and also as a PIC32 programmer (used for updating the Micromite firmware). This is called the Microbridge and when it is acting as a USB-to-serial interface, it creates a virtual serial port on your computer. This acts like a normal serial port, but it works over USB. As mentioned above, we introduced the Microbridge in the May 2018 issue of PE, and it is used in the later versions of the Micromite LCD Backpack (for V2, see May 2018; and V3 in August 2020). The Microbridge connects your computer to the Micromite’s serial console. This is the main programming interface to the Micromite, and you can use it to set options, enter programs, run them, get feedback from running programs and also receive data. If you’re running Windows, it will automatically create a virtual serial interface when the Explore-28 is plugged into a USB socket on your computer. This appears as a COM port, usually with a high number such as COM5 or COM21. On Windows 7 and earlier versions, a device driver may be required (see https://bit.ly/pe-sep20-win7), but Windows 8 and 10 already have the driver built in. You can check the COM number that Windows allocated to the Explore-28 by going into Device Manager and looking for a new device listed under Serial Ports, as illustrated in Fig.2. The Linux kernel and macOS operating systems usually do not need any special configuration and, as an example, under Linux Mint, the Explore-28 normally appears as: /dev/ttyACM0. Accessing the Micromite console When you plug the Explore-28 into your computer, the LED marked ‘PWR’ (LED1) will illuminate, to show that it is powered. To access the Micromite’s console, you need to run a terminal emulator on your computer. This takes the key presses that you make and sends them down the serial interface to the Micromite, while also displaying any responses from the Micromite. For Windows, you have several choices. We recommend Tera Term (http:// tera-term.en.lo4d.com/), but there are many other terminal emulators to choose from, with some specially written for the Micromite (see the Micromite resources panel). The Micromite’s console defaults to a speed of 38,400 baud, so all you need to do is configure your terminal emulator for the correct COM port number and this baud rate. Then, when you press Enter, you should see the Micromite command prompt (a greater than symbol: ‘>’), as shown in Fig.3. At this point, you have full control of the Micromite for entering commands or setting options. You can experiment by typing PRINT 1/7 and pressing Enter. The 25 The Mighty Micromite The Micromite is based on the Microchip PIC32, which is a high-performance 32-bit microcontroller. While this chip as supplied is powerful, it is not that easy to write programs for it (the manuals run to over a thousand pages!) and the standard programming languages used on it are assembler, C or C++. These languages and the programming software are complex and require experience to use properly. For the average hobbyist, the Micromite firmware makes programming much easier. It’s loaded into the Flash memory of the PIC32 and turns the chip into a Micromite. The Micromite firmware insulates you from the complexities of the underlying silicon, while still allowing you to use its features. To program the Micromite, you use the BASIC programming language, which is designed to be easy for beginners and allows you to get started almost immediately. The BASIC language The following is an elementary introduction to Micromite programming. We published a comprehensive three-part series on using the Micromite in the February to April 2017 issues, so refer to those articles for more detailed instruction. Plus of course the ongoing Make it with Micromite series. The Micromite version of BASIC is called MMBasic (short for MicroMite BASIC) which is loosely based on the Microsoft BASIC interpreter that was popular years ago. ‘Interpreted’ means that the firmware reads through your program line-by-line, executing each command as it finds them. BASIC (an acronym for Beginner’s All-purpose Symbolic Instruction Code) was initially developed by Dartmouth College in the US for teaching programming, and therefore emphasises ease of use. BASIC is also a powerful language, and it became popular in the 1980s and 90s with the introduction of small computers such as the Commodore 64 and Apple II. These days, it is still used in some large commercial data systems (usually running Pick Basic). BASIC program execution starts at the top of the program and continues until it runs off the bottom or hits an END command. Generally, there is one command per line, although you can have more if you wish, each separated by the colon (:) character. A command can be something like PRINT which will output some text to the console, PIN() which will set the state of an output pin, or SERVO which will control a servo motor. Decisions within the program are made using the IF…THEN command. So, for example, your program can include something like: IF t > 30 THEN PRINT “too high” Your program can also run commands in loops. For example, the following will display the numbers from one to ten: FOR nbr = 1 to 10 PRINT nbr NEXT nbr Micromite input/output The Micromite is intended to be a controller that can be embedded in something like a burglar alarm or process controller. In this type of role, its ability to use the I/O pins to control external devices is critical. Micromite will return the result of dividing 1 by 7, then display the command prompt again. This is called ‘command mode’ and it allows you to try out most BASIC commands at the command prompt. It is handy for testing commands while you are learning the language. Note that when you type something on the console or the Micromite sends some data to your PC, the LED marked 26 An I/O pin refers to the physical pin on the Micromite chip. On the Explore-28, these are routed to pin headers on the edge of the module, with the same numbering. So, when you refer to a pin number in your program, that is both the physical pin on the chip and the pin header number. In MMBasic, you configure an I/O pin on the chip using the SETPIN command – it defines the pin as a digital input, digital output or analogue input. For example, if pin 2 on the chip has been defined as an analogue input, the function PIN(2) will read the voltage on pin number 2; eg: PRINT PIN(2) would create a simple voltmeter. To read the state of a pin configured as a digital input, you use the same function, but in that case, it will return zero for a low voltage and one for voltage high. You can set the output level of a pin configured as a digital output by assigning a value to PIN(). For example, this will set the output on pin 24 to a logic high (3.3V): PIN(24) = 1 There are many other things that you can do with the Micromite’s I/O pins, including measuring frequency, timing, generating square waves and more. Special device support A great feature of the Micromite is that it has built-in support for many external devices like temperature and humidity sensors, keypads, real-time clocks and servos. For example, using the IR command, you can receive commands from an infrared remote control. This is easy to do, and it adds flair (and utility) to your project when you can control it by pressing a button on a remote control. As another example, you can connect a low-cost ultrasonic distance sensor to the Micromite and with one function, read the distance to an object in centimetres. Measuring temperature and humidity is just as easy; MMBasic will query the sensor for you and return the temperature in degrees Celsius and humidity in %RH. Perhaps the most outstanding feature of the Micromite is its ability to control a touch-sensitive LCD panel. The Micromite can display text and graphics and respond to touch inputs on the panel’s face. Communications protocols There are many modules and chips that you can buy to measure anything from air quality to acceleration. These all send their data via some communication protocol, usually serial, and the Micromite supports four main protocols: • Asynchronous serial, which is used by computers, lab equipment and GPS modules. • I2C, which is used by gas sensors, real-time clocks and many other chips. • SPI, which is used, for example, by accelerometers, memory chips and electronic compasses. • Dallas One-Wire, which is mostly used for temperature sensors. GPS modules are particularly valuable; they’re cheap (£8-20) and give you your precise location, altitude, speed, heading and the exact time. Using the Micromite’s serial interface, it is easy to retrieve this information and they open up a world of exciting projects that can be built. ‘MODE’ (LED2) will briefly flash to indicate that data is being sent over the virtual serial port. The tactile pushbutton near the LEDs (switch S1) is used to put the Microbridge into its programming mode (more about that later). A handy feature of the Microbridge is that you can reset the chip by sending a break signal over the virtual serial interface. In Tera Term, this is done by pressing ALT-B, and this has the same effect as cycling the power to the Micromite. Programming example We mentioned how easy it is to get started with the Explore-28, so here is a short tutorial to illustrate that point.For a beginner, the best method of entering a program into the Micromite is to use the Micromite’s built-in full-screen editor. Practical Electronics | September | 2020 This is fully documented in the Micromite User Manual, but to get started, all you need to know is that the arrow keys on your keyboard will move the cursor around the text and the backspace key will delete the character before the cursor. At the command prompt, type EDIT followed by the Enter key. This will take you into the Micromite’s editor. Then, enter this short program: SETPIN 15, DOUT DO PIN(15) = 1 PAUSE 500 PIN(15) = 0 PAUSE 500 LOOP To save this program, press the F1 key or CTRL-Q (which does the same thing). This will return you to the command prompt. Then, to run the program, type RUN and press Enter. This program toggles the voltage on pin 15 of the Explore-28 from zero to 3.3V and then back again every second, and continues doing it forever. You can test this by probing pin 15 with a voltmeter, and you should see the voltage jumping up and down at 1Hz. While the program is running, you will not see the command prompt in the terminal emulator. This is because the Micromite is now busy, but you can regain control by pressing CTRL-C. This is the break key and it will interrupt any running program and return control to the command prompt, so that you can edit the program or enter other commands. Circuit description The circuit of the Explore-28 is shown in Fig.4. As you can see, it isn’t terribly complex. It consists of three main components: IC1, the 28-pin PIC32 microcontroller (the Micromite); IC2, the PIC16F1455 (Microbridge) which provides the USB interface; and a voltage regulator to provide the 3.3V supply (REG1). The PIC32 used for the Micromite (IC1) is in a 28-pin surface-mounting package, with most of its pins going directly to the header pins on the edge of the board (CON1-CON3). The 10µF capacitor on pin 20 is critical and must be a high-quality multilayer ceramic type. It is used to stabilise the chip’s internal 1.8V regulator, and if it is missing or the wrong type is used, the Micromite will not work. The only Micromite pins which do not go directly to a corresponding pin on CON1-CON3 are: pin 11, the serial data out line, which goes via a 1.5kΩ resistor in order to protect IC1 if an Practical Electronics | September | 2020 external device attempts to drive it above +3.3V or below 0V (eg, a raw RS-232 signal); and pin 20 (VCAP), as this micro pin is already connected to the required capacitor. Several of the micro’s pins also connect to the Microbridge (IC2), to allow the Microbridge to reprogram the chip and for its USB/serial function. As mentioned earlier, the Microbridge chip has two functions; it acts as a USB-to-serial bridge and as a PIC32 programmer. On power-up, it starts in the USB-toserial bridge mode, with the MODE LED (LED2) off, except for flickering when there is serial activity. Serial data is transmitted from pin 6, which connects to the receive data pin (pin 12) on IC1. Similarly, the Micromite’s transmit pin (pin 11) connects to receive (pin 5) on the Microbridge chip. A second 1.5kΩ resistor between the TX pin of IC2 (pin 6) and the RX pin of IC1 (in 12) protects IC2 in case external circuitry tries to send data to the Micromite while the Microbridge is active. A 10kΩ pull-up resistor from 3.3V to pin 11 of IC1 prevents glitches on the serial port when the Micromite is reset. Another 10kΩ pull-up resistor on pin 1 (MCLR) prevents spurious resets of the chip. The tactile switch on pin 4 of IC2 is used to place the Microbridge into its PIC32 programming mode. In this mode, the MODE LED (LED2) lights up, and the Microbridge chip uses pin 7 to reset the PIC32 and pins 2 and 3 to drive its programming interface. In normal operation, these pins are in a high-impedance state, so the corresponding I/O pins on the Micromite can be used for other purposes. The Explore-28 is just a little larger than the original 28-pin Micromite in a standard dual inline plastic (DIP) package. But it has many more features, including a USB-to-serial interface, onboard PIC32 programmer and a 3.3V regulator. Parts list – Micromite Explore-28 1 four-layer PCB coded 07108191, 39 × 18.5mm 1 15-pin male header, 2.54mm pitch (CON1) 1 6-pin and 8-pin male header, 2.54mm pitch (CON2,CON3) (optional) 1 mini type-B SMD USB socket (CON4) [Altronics P1308, element14 2300434] 1 mini SMD tactile pushbutton switch (S1) [element14 1629616] Semiconductors 1 PIC32MX170F256B-50I/SO microcontroller programmed with MMBasic, SOIC-28 (IC1) 1 PIC16F1455-I/SL microcontroller programmed for Microbridge, SOIC14 (IC2) 1 MCP1703A-3302E/DB low-dropout 3.3V regulator, SOT-223 (REG1) 2 red SMD LEDs, 2012/0805-size (LED1,LED2) Capacitors (all SMD 2012/0805 ceramic) 1 10µF 6.3V X5R 2 4.7µF 16V X5R 2 100nF 50V X7R Resistors (all 1% SMD 2012/0805) (Code 103) 2 10kΩ (Code 152) 4 1.5kΩ (Code 100) 1 10Ω The power supply is based on a lowdropout linear regulator (REG1; Microchip MCP1703) with a fixed output of 3.3V. This powers both the Microbridge chip (IC2) and the Micromite (IC1) and as mentioned, is also made available on pin 13 of CON1 for external circuitry to use. The MCP1703 can source up to 250mA, with about 50mA of that being used by the Microbridge and the Micromite. Besides the critical 10µF capacitor described above, there are two 100nF bypass capacitors for the 3.3V supplies of IC1 and IC2, plus 4.7µF input bypassing and output filtering ceramic capacitors for REG1. PIC32 programmer We mentioned above that the Microbridge chip can act as a PIC32 programmer for loading firmware updates into the Micromite (IC1). You essentially get this feature for free, which is handy, as previously you needed to purchase a separate PIC32 programmer to take advantage of new releases of the Micromite firmware. If you purchased the Explore-28 as a fully assembled module or a kit, 27 both microcontrollers (the PIC32 and PIC16F1455) will be supplied pre-programmed, so this programming feature is only required if you want to update the firmware with a new release. The process of loading new firmware into the Micromite is painless and only takes a minute or two. Start by switching the Microbridge into its programming mode and then, using free software on your laptop, you upload the new firmware via USB to the Microbridge, which in turn programs it into the flash memory of the Micromite. To enter into the programming mode, momentarily press the tactile switch on the Explore-28. The Microbridge chip will then immediately switch to its PIC32 programming mode, and the MODE LED will illuminate to confirm this. If you did not intend to enter this mode, you can revert to the USB-to-serial mode by simply cycling the power. The software you need to reprogram the Micromite is called pic32prog. The Windows version is available from the September 2020 page of the PE website, while the macOS and Linux versions are available from other sites. The Windows version does not need to be installed; you can copy the executable to a convenient location and start a command window in that folder. New versions of the Micromite firmware can be found at the author’s website, http://geoffg.net/micromite.html (scroll to the bottom of the page). The Micromite firmware download on the PE website is also updated periodically, but there may be a delay between a new release and it appearing on our website. Generally, the firmware is contained in a .zip file, along with the Micromite manuals, so you need to unzip its contents and locate the firmware file (it has a .hex extension). Then, copy this file to the same folder as the pic32prog program. Programming the firmware To program this file into the Micromite chip, run pic32prog with the following arguments: pic32prog -d ascii:comxx yyyy.hex Here, xx is the COM port number and yyyy.hex is the name of the firmware file. The COM port number is the same as that allocated by Windows when the Microbridge was in its USB-to-serial converter mode. As an example, if your Microbridge was allocated the virtual serial port of COM23 and the file that you wanted to program was Micromite_V5.05.09.hex, the command would be: pic32prog -d ascii:com23 Micromite_V5.05.09.hex Before you do this, make sure that you have closed the terminal emulator that you were previously using to communicate with the Microbridge in its USB-toserial mode. Not doing this is a common mistake and it will cause pic32prog to abort with an error message, because it cannot open the virtual serial port. When you press enter at the end of this command, pic32prog will upload the hex file to the Microbridge, program it into the PIC32, then read back the programmed data to verify that the programming operation was executed correctly. The whole operation will take less than a minute and sample output of the whole process is shown in Fig.5. After the programming operation, the MODE LED will switch off, the Microbridge will revert to operating as a USBto-serial converter, and the Micromite will automatically restart with the new firmware. Updating the Micromite’s firmware will reset any options set and completely erase the BASIC program memory. So make sure that you make a copy of the program stored on the Micromite before starting the upgrade. Micromite Explore 28 Fig.4: the circuit of the Explore-28 module is elegant in its simplicity. IC1 is the PIC32 which runs MMBasic; IC2 is the Microbridge which provides a USB serial port and the ability to reprogram IC1; and REG1 is a low-dropout regulator which provides both ICs with a 3.3V supply rail, derived from USB 5V or a source of 4-16V DC fed in via CON1 and/or CON2. 28 Construction Because the Explore-28 is readily available as an assembled module, we expect that many readers will take that option. However, if you decide to assemble your own module, you will find that it is not hard but you will need a steady hand and ideally, some experience soldering surfacemount components, even though the ones used in this project are not that small (at least, by SMD standards). We have often covered soldering surface mounted components before, and Practical Electronics | September | 2020 using them is nothing to be feared. The secret is to use plenty of flux paste and keep only a small amount of solder on the soldering iron’s tip. The flux makes the solder flow smoothly around the joint while using only a minimal amount of solder means that you will avoid solder bridges and blobs. The PCB used for the Explore-28 is a four-layer board, coded 07108191, measures 39 × 18.5mm, and has components mounted on both sides. It is available from the PE PCB Service. The overlay diagrams, Figs.6(a) and (b), show where the components are mounted, along with top and bottom layer tracks. We haven’t shown the two inner layers because that would make the diagrams hard to read. The outer layer tracks shown are used for signal routing, while the two inner layers consist of a ground plane and a power (+3.3V) plane. These cover most of the board and only have holes where vias pass between the top and bottom layers. Other vias are used to connect these planes to component pins. While Fig.6 shows where all the components need to be mounted, the silk screen printing on the board will also guide you during assembly. It’s best to solder the SMD components on the bottom side first (the side with IC2 and REG1), then add the components to the top side, and finish with the pin headers. Before soldering IC2, if you haven’t purchased a pre-programmed kit, you need to program it with the Microbridge firmware. This can be downloaded from the PE website or from: Fig.5: the typical output from pic32prog after it has programmed a new version of the MMBasic firmware into the Micromite using the Microbridge. The whole operation is straight forward and takes less than a minute. http://geoffg.net/microbridge.html (scroll to the bottom of the page). You will also need a narrow SOIC programming socket to do this, so unless you have one, you’re better off acquiring a programmed chip. You do not need to program the PIC32 microcontroller used for the Micromite because the Microbridge will do that for you when you have finished construction. Solder IC2 on the bottom side of the board first, taking care that its pin 1 dot is oriented towards the nearby empty square pads, as shown in Fig.6. If you bridge two pins with solder, clean up the bridge by applying a little flux paste and then solder wick. CON2/3 (UNDER) 28 Follow with REG1, which can only go in one way around. It’s best to apply a little flux paste to the large pad first, then solder the three smaller pins before finishing with the large tab. You may need to turn your iron up to get a good solder joint on the tab. Now add the seven resistors and five capacitors to the bottom side, being careful not get any of the different values mixed up. Flip the board over and then solder the USB socket. Make sure its five signal pins line up correctly with the pads (aided by the two plastic posts going into holes on the board), then solder those signal pins and ensure there are no bridges between them. CON2 /3 (UNDER) 28 15 5V 15 5V K CON4 IC1 K 1 S1 1 CON1 (UNDER) 14 5V LED2 MODE ACTUAL SIZE 1.5kW 10kW 1.5kW 10W 1 100nF IC2 100nF 28 1.5kW (b) CON1 1 1.5kW 10mF CON2/3 IC1 K S1 CON4 4.7mF 1 REG1 4.7mF 15 5V Fig.6: use these same-size photos and PCB overlay diagrams (top and bottom view) as a guide to assembling the Explore-28. Because the Micromite Explore-28 is so small, we’ve also prepared the twice-life-size diagrams at right to make life a little easier! As mentioned in the text, it’s easiest to populate the bottom side first (with IC2 and REG1) since these components are all similar heights, so the board should still sit relatively flat while you solder the remaining components on the top side. If you’re having trouble getting it to sit flat, try plugging a pair of 15-pin headers into a breadboard and then resting the PCB on top. Practical Electronics | September | 2020 K 14 5V 10kW 1 LED1 PWR 1 (a) 14 CON1 (UNDER) 5V 2:1 SCALE FOR CLARITY (DOUBLE ACTUAL WIDTH & HEIGHT) 1 1.5k CON1 10k 10 100nF 28 1.5k IC2 100nF 5V 4.7 F 1.5k 1 1.5k 14 10k 1 10 F REG1 4.7 F CON2/3 15 5V 29 to indicate the cathode, we’ve seen LEDs where it indicates the anode. So to be extra safe (and avoid a lot of fiddly rotating of components later), it’s best to probe each end of the LEDs with a multimeter set on diode-test mode. When they light up, the red probe is on the anode and the black probe on the cathode. Finish up by soldering pushbutton S1 in place, followed by the headers, fitted to the underside of the board as shown. Testing To test the completed Explore-28, simply connect it to a USB port on your computer and program the latest firmware The Explore-28 is designed to plug into a standard into the Micromite as (solderless) breadboard for easy prototyping. Using the pre-assembled module, you can plug it into a described above (if your USB port on your laptop, and in a few minutes have Micromite chip wasn’t ala simple program running. ready programmed). Then check that you If there are bridges, apply some flux can get the MMBasic command paste and clean them up using solder prompt via a terminal emulator. If wick. Then solder the four large mount- you can, it means that everything is ing tabs, to hold the socket firmly to working perfectly. If you do not see the virtual serial the board. port created by the Microbridge on your With that done, you can continue computer, the first thing to check is that with soldering IC1; again, watch its orientation – pin 1 goes at the opposite the voltage regulator is producing 3.3V (measure between pins 13 and 8). end from the USB socket. If this is OK, then the Microbridge Then fit LED1 and LED2, with their chip is probably at fault, with the most cathodes (generally indicated with a green stripe or dot) towards the ‘K’ likely causes being poor soldering or an shown in Fig.6 (shown on the PCB itself incorrectly programmed chip. If you can connect via the USB-toas white squares). But note that while serial interface but you do not see the most LEDs have a green dot or stripe Where to buy the Explore-28... ... parts, kits and modules • A full kit, major parts or a complete pre-assembled module is available from the dedicated UK Micromite store at: https://micromite.org/ • Also visit the Rictech Ltd website for a downloadable construction pack with PCB and firmware: www.rictech.nz/micromite-products Micromite’s prompt, you should check that the Micromite was programmed correctly, that the capacitor on pin 20 is of the correct type and, of course, that your soldering is good. A handy check is the current drawn by the completed module. This is normally about 36mA. You would need to connect an ammeter between a 4-16V DC supply and the bottom row of pins on the board to measure this. If it is closer to 15mA, the Micromite chip is not running correctly, while a current draw of less than 5mA points to a problem with the voltage regulator. So, there you have it. The Explore-28 is an easy-to-use microcontroller module that you can use as the brains of your next project. It is a fun electronic building block to play with and an excellent way of learning to program in the BASIC programming language. Reproduced by arrangement with SILICON CHIP magazine 2020. www.siliconchip.com.au Micromite Resources Latest firmware versions, manuals and tutorials: ..................................................................................................... http://geoffg.net ‘Getting Started with the Micromite’ and ‘Micromite User Manual’: ........................... http://geoffg.net/micromite.html#Downloads The Back Shed forum, where many knowledgeable users can help newcomers: .... www.thebackshed.com/forum/Microcontrollers Microbridge Resources Firmware for the Microbridge (PIC16F1455) in the Explore-28: .............................. http://geoffg.net/microbridge.html#Downloads pic32prog, used to program new firmware into the Micromite (Windows):............. http://geoffg.net/microbridge.html#Downloads P32P, a user-friendly GUI interface for pic32prog.exe (Windows): .... www.thebackshed.com/docregister/ViewDoc.asp?DocID=21 Terminal Emulators Tera Term, the standard terminal emulator used with the Micromite: .................................................. http://tera-term.en.lo4d.com/ GFXterm, a terminal emulator designed specifically for use with the Micromite. It works with the Micromite’s built-in editor and supports a set of graphics extensions: ................. www.thebackshed.com/docregister/ViewDoc.asp?DocID=22 MMEdit, a complete IDE (Integrated Development Environment) specifically designed for the Micromite. It includes advanced features such as colour-coded text, formatting, download and run, and more: ............ www.c-com.com.au/MMedit.htm 30 Practical Electronics | September | 2020