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By Nicholas Vinen Based on Geoff Graham’s Micromite Plus & Micromite LCD BackPack The Micromite Plus LCD BackPack The Explore 64 and the Micromite LCD BackPack have had an illicit affair and here are the secret baby photos to prove it! It has its mother’s eyes and father’s brain. OK, that’s not really true; what we have done is taken the best features of each project and put them together onto a single board. Use it to supercharge your BackPack project or just as a convenient and cost-effective controller module. R EADERS WILL have noticed that we’ve published a number of projects based on the Micromite LCD BackPack, first described in our February 2016 issue. It’s a very convenient way of providing user control and feedback for a project and combines the user interface and control logic in a compact module. Because it doesn’t cost too much, we can integrate it into a larger project without making it overly expensive. And thanks to Geoff Graham’s MMBasic interpreter, constructors can easily upgrade and modify our designs. As it stands, the biggest problem with the BackPack is the limitation 64  Silicon Chip of the DIP (through-hole) PIC32 processor. It has significantly less flash memory and RAM and a much lower operating frequency compared to the surface-mount versions. The BASIC interpreter overhead exacerbates all of these. It also lacks the SD card and USB interfaces introduced with the Micromite Plus in the August issue. The micro used in the Micromite Plus Explore 64/100 projects puts the original to shame, with a much more generous helping of RAM and flash, much better speed (2.5 times as fast) and sufficient spare memory and pins to implement onboard microSD card and USB interfaces. But while the Ex- plore 64 can interface with many different displays, you have to wire it up yourself and the 5-inch touchscreen is quite expensive. So those projects can’t easily replace the LCD BackPack. But this one can! We have combined the convenience and low cost of the original BackPack with all those new Micromite Plus features. The Micromite Plus LCD BackPack uses the same 2.8-inch touchscreen TFT as before but has the enhanced processor and peripherals of the Explore 64. Backwards compatibility One of the main aims when designing the Plus BackPack was to make it siliconchip.com.au easy to improve projects that used the original BackPack. The original BackPack has three main connectors: one for 5V power and the serial terminal (CON1, four pins), one for the TFT interface (CON3, 14 pins) and one for interfacing to external circuitry (CON2, 18 pins). It also has an in-circuit serial programming (ICSP) connector for the microcontroller (CON4, six pins). On the Micromite Plus LCD BackPack, we have fitted identical connectors, with the same names, positions and sizes. The PCB is the same size too, with mounting holes in the same positions. So it’s largely a “drop-in” replacement. There are differences, however, in some of the pin numbers and properties assigned to these connectors. Going through each connector in turn, these differences are: • CON1: the pinout is still 5V/Tx/ Rx/GND, however the Micromite Plus uses pins 58 and 6 as the console Tx and Rx, compared to pins 11 and 12 on the original Micromite and the Micromite Mk2. However, the difference in these pin numbers should not affect usage at all. • CON2: we have kept the functions of each pin in this I/O header as close as possible to those for the original BackPack. However to keep the functions identical, we had to change most of the pin numbers. That means that you will need to change the software to use the new pin numbers – see Table 1 for a comparison. Note that this same information is also shown in the circuit diagram which is discussed below. There are only two small losses of function in this header (this was unavoidable). First, pins 8 and 11 are no longer 5V-tolerant and second, pins 9 and 10 can no longer operate as count inputs. But there are two extra benefits to the new configuration: four new analog-capable inputs at pins 5, 6, 8 and 11 and the SPI bus is no longer shared with the one driving the TFT and touch sensor. • CON3: this is intended to plug into the same ILI9341-based TFT display as the original BackPack. The pin functions are essentially the same although again, some of the numbers have changed and thus the display/ touch initialisation commands have changed (we’ll go over this later). Table 2 shows how the pins are connected to the display board on both the original and new designs. siliconchip.com.au Features & Specifications • Display: 65,536 colour, 2.8-inch (7cm) diagonal TFT LCD with 320 x 240 pixel resolution and software backlight brightness control • • Input system: resistive touchscreen • • Available memory: 100KB flash program space, 100KB RAM • • Digital I/O current capability: 15mA sink/source • • USB support: Integrated USB 2.0 interface with virtual serial port • Interpreter: Built-in MMBasic with support for 64-bit integers, floating point, strings, arrays and user-defined subroutines and functions • Standard Micromite features: includes built-in communications protocols, PWM and SERVO outputs, variable CPU speed, sleep mode, watchdog timer and automatic start & run • Additional features: built-in support for infrared remote receivers, temperature sensors, humidity sensors, distance sensors, numeric keypads and battery-backed real-time clocks • Graphics commands: CLS, PIXEL, LINE, BOX, RBOX, CIRCLE, TEXT and BITMAP, using the full range of colours • Advanced graphics commands: these include on-screen keyboards, buttons, switches, check boxes and radio buttons • • • Font support: six built-in fonts plus the ability to load custom user fonts • • Dimensions: 50 x 86 x 27mm (same as original LCD BackPack) • Overall cost: similar to original LCD BackPack Processor: Microchip 32-bit 120MHz microcontroller with 512KB flash memory and 128KB RAM I/Os: 31 free input/output pins including 17 analog inputs, 14 5V-tolerant pins, hardware SPI and I2C buses, two (or three) serial ports, four PWM outputs, a PS/2 keyboard interface, three frequency counting inputs, a wake-up pin (for sleep mode) and an infrared input pin Communications protocols: SPI, I2C, asynchronous serial, RS-232, IEEE 485 and Dallas 1-Wire SD card support: handles cards up to 64GB with onboard microSD socket and SD card socket on back of display module Code editing: on-screen editor support when PS/2 keyboard is connected Power supply: 5V (4.5-5.5V) <at> 80mA (backlight off) up to 250mA (backlight at full brightness) Compatibility: connector positions and pin-outs compatible with original LCD BackPack As noted earlier, the SPI2 bus is used for the TFT (this is required by MMBasic) while the SPI1 bus is connected to CON2, for interfacing with external circuitry. This has a major advantage compared to the original BackPack as MMBasic’s use of the SPI bus for graphics commands and touch sensing will not interfere with SPI data sent via CON2. This is especially helpful when using touch interrupts or using the SPI bus or graphics commands in interrupt handler routines. Another major improvement over the original BackPack is the deletion of VR1 for TFT backlight control. The backlight is now driven by a Mosfet which can have its gate controlled via the PWM2A output for software-controlled dimming over a wide range. The backlight can be turned off entirely when not used, which is especially helpful for battery-powered devices as it typically draws most of the supply current. • CON4: the ICSP header is connected to PGED1/PGEC1 in both versions, which are pins 4 and 5 on the original November 2016  65 Table 1: CON2 Functions In Original BackPack vs Plus BackPack Pin Number Original BackPack Plus BackPack 1 RESET RESET 2 3 SPI OUT 8 SPI1 OUT 3 4 12 4 5 14 5 9 COM2:TX 11 COM2:TX 6 10 COM2:RX 13 COM2:RX 7 14 SPI IN 45 SPI1 IN 8 16 COUNT/WAKEUP/IR 51 COUNT/WAKEUP/IR 9 17 COUNT/I2C 44 I2C CLOCK CLOCK 10 18 COUNT/I2C DATA 43 I2C DATA 11 21 COM1:TX 15 COM1:TX 12 22 COM1:RX 59 COM1:RX 13 24 24 14 25 SPI CLK 50 SPI1 CLK 15 26 27 16 +3.3V +3.3V 17 +5V +5V 18 GND GND Note: blue indicates analog pin. Red indicate 5V-tolerant pin. Table 2: CON3 Functions In Original BackPack vs Plus BackPack Pin Number TFT Pin Original BackPack Plus BackPack 1 VCC +5V +5V 2 GND GND GND 3 CS-bar 6 PWM1C 29 4 RESET 23 23 COUNT 5 D/C 2 2 6 SDI (MOSI) 3 SPI OUT 5 SPI2 OUT 7 SCK 25 SPI CLK 4 SPI2 CLK 8 LED (backlight) to VR1 to pin 53 (PWM2A) via Q1 & Q2 9 SDO (MOSI) 14 SPI IN 47 SPI2 IN/PWM2B 10 T_CLK 25 SPI CLK 4 SPI2 CLK 11 T_CS 7 COM1:ENABLE 1 12 T_DIN 3 SPI OUT 5 SPI2 OUT 13 T_DO 14 SPI IN 47 SPI2 IN/PWM2B 14 T_IRQ 15 COUNT 3 BackPack and pins 16 and 15 on the Plus BackPack. On the original BackPack, these pins were also routed to CON2 and so the external circuit design had to take this into account if the chip could be re-programmed in-situ. In contrast, on the Plus BackPack, 66  Silicon Chip only pin 11 on CON2 (pin 21 of the micro, COM1:TX) is so affected. The other programming pin is routed to new header CON5 and will rarely be used. So in summary, to adapt software designed for the original LCD BackPack to the Plus BackPack, I/O pin numbers will need to be adjusted and you will need to ensure that you use the SPI1 bus and that pins 8 and 11 of CON2 are not required to be 5V-tolerant. New features Five new connectors have been added, with the following functions: • CON6: since the Micromite Plus has many more I/O pins than the original Micromite, we’ve added this extra 21-pin header to give access to most of those additional pins, for projects which may exhaust the connections available on CON2. This connector’s pin-out has some similarities to CON6 on the Explore 64. However, we’ve had to use a number of different pins here because the others were already in use for other purposes. In summary, the pins on CON6 consist of nine analog-capable inputs, 11 5V-tolerant digital inputs, four PWMcapable outputs, two pins which can be used to connect a PS/2 keyboard, two counting inputs plus the same 3-pin SPI bus which is wired to CON2. Note that besides this shared SPI bus, none of the other pins are used for any other purpose and thus you are free to do what you like with them (with one slight exception, see the following section). • CON5: this 3-pin header provides a convenient place to connect to the COM3 Tx/Rx pins (16 & 17 on IC1) as well as pin 33, if it is not being used as USBID (ie, if shorting block SB1 is not shorted). Unless you need to use the COM3 port, you’re unlikely to need this header and it can be left off. Note that pins 16 & 17 are already connected to CON4 and CON6 respectively, however since CON4 is for incircuit programming, you would not want to connect a COM port there. Note also that pin 33, USBID is only really needed for “USB on-the-go” (USB OTG) which would probably require a different connector for CON8 and thus is most useful as a 5V-tolerant general purpose digital input; it can not operate as an output. • CON7: this allows the use of the SD card socket on the TFT module. To use this, you need to fit a 4-pin female socket in this location and a matching pin header on the back of the TFT module. The SD card’s CS-bar, MOSI, MISO and SCK lines are routed to pins 21, 5, 47 and 4 on IC1 respectively. Since the latter three pins are SPI2 OUT, SPI2 IN and SPI2 CLK, this makes interfacing siliconchip.com.au with an SD card easy; the commands to do this are shown later. Power for the SD card on the TFT module comes from a 3.3V regulator (on the module) that draws from the 5V supplied via CON3. So one advantage of using that SD card socket is that it doesn’t reduce the current available from the 3.3V rail on the BackPack PCB. • CON8: the onboard USB socket which can be used as a serial console. It’s quite convenient since all you need is a USB Type-A to microUSB cable to communicate with the Micromite Plus. However as noted in the earlier articles on the Micromite Plus, it has the disadvantage that the console is reset whenever the micro is reset (eg, when S1 is pressed). However, our experience has been that this is not necessary very often so you certainly can program the Micromite Plus via this port. If JP1 is fitted, then the unit will be powered from this cable as well but take care that you don’t back-feed 5V into the USB port since this could damage your PC. In other words, only fit JP1 if you are not powering the board from any other source. The alternative to using CON8 for programming and communications is to use a USB/serial adaptor (as explained in multiple previous articles) and wire it up to CON1 (see Fig.3). This will allow the serial port to continue operating even if the Plus BackPack is reset. Power can also be supplied to the board via CON1, with the same proviso as above. • CON9: the onboard microSD card socket. This is wired in parallel with CON7 so if using this, you can’t use the SD card socket on the TFT module and vice versa. The card is powered directly from the onboard 3.3V supply (from lowdropout linear regulator REG1) and is provided with a 10µF bypass capacitor. The only additional connection is from pin 22 of IC1 to the card detect switch on the socket. Later on, we’ll show the command to configure the Micromite to use this pin to detect card insertions and removals. Circuit description The full circuit of the Micromite Plus BackPack board is shown in Fig.1. It consists mostly of microcontroller IC1 and its connections to CON1CON9, so essentially we have already siliconchip.com.au Parts List 1 double-sided PCB, code 07110161, 86 x 50mm 1 ILI9341-based LCD module, 320 x 240 pixels, 2.8-inch diagonal, with touch controller 1 right-angle, through-hole, tactile pushbutton switch, short actuator (S1) 1 20MHz crystal, low profile HC-49 (X1) 2 4-pin headers, 2.54mm pitch (CON1 & SD card connector on display module) 1 18-pin header, 2.54mm pitch (CON2) 1 14-pin female header, 2.54mm pitch (CON3) 1 6-pin right-angle header, 2.54mm pitch (CON4; optional) 1 3-pin header, 2.54mm pitch (CON5; optional) 1 21-pin header, 2.54mm pitch (CON6) 1 4-pin female header, 2.54mm pitch (CON7) 1 SMD mini USB type B socket (CON8) (Altronics P1308 or similar) 1 microSD card socket (CON9) (Altronics P5717 or similar) 1 2-pin header, 2.54mm pitch, with shorting block (JP1) 4 M3 x 12mm tapped spacers 4 M3 x 6mm machine screws 4 M3 x 8mm machine screws 4 Nylon washers, 3mm ID, 6mm OD, 1mm thickness 1 laser-cut jiffy box lid and UB5 jiffy box (optional) 1 USB-to-serial adaptor and jumper leads (optional, see text) described most of it above. But let’s go over a few details. IC1 has a 20MHz crystal connected between oscillator pins 39 and 40, with 22pF load capacitors. Its 100MHz or 120MHz clock signal is derived from this using an internal PLL (phaselocked loop) frequency multiplier that’s configured by the MMBasic software. A 10µF ceramic capacitor from pin 56 to ground stabilises its internal core supply rail. Display backlight control is via IC1’s output pin 53, referred to in MMBasic as PWM 2A. Note that the PWM 2B function is shared with SPI2 IN, which is already dedicated to the display in- 1 5V regulated power supply (see text) Semiconductors 1 PIC32MX470F512H-120/PT microcontroller programmed with 0710816A.HEX (IC1) 1 MCP1703A(T)-3302E/DB low-dropout 3.3V regulator, SOT-223 (REG1) 1 MCP120(T)-270I/TT 2.7V supply supervisor, SOT-23 (IC2; optional – see text) 1 DMP2215L P-channel Mosfet, SOT-23 (Q1) 1 2N7002 N-channel Mosfet, SOT-23 (Q2) 1 green SMD LED* (LED1) Capacitors* 4 10µF 6.3V ceramic, X5R or X7R 6 100nF 50V ceramic, X5R or X7R 2 22pF ceramic, C0G/NP0 Resistors (1% or 5%)* 2 10kΩ 1 470Ω 2 1kΩ 1 10Ω * Use SMD 3216 (1206 imperial) size; 2012/0805 sizes are also suitable but are not recommended for beginners Where to buy parts A complete kit for the Micromite Plus LCD BackPack will be available from the SILICON CHIP online shop, along with suitable laser-cut lids and separate items such as the PCB and programmed microcontroller. terface, so there is no issue with interaction between these two PWM functions that share the same timer. Pin 53 drives the gate of N-channel Mosfet Q2, which has a 10kΩ pull-down resistor so that it is held off when the microcontroller is powering up, reset or not operating for some other reason. When pin 53 goes high, Q2 switches on and this pulls the gate of P-channel Mosfet Q1 low. It is normally held high by a 1kΩ resistor from the 5V rail. When the gate of Q1 is pulled low, Q1 switches on, allowing power to flow from the 5V rail into the backlight LED anode pin, marked LED on CON3. The higher the duty cycle of the PWM sigNovember 2016  67 10 µF X5R Tx Rx CON6 +3.3V OUT IN PWM1B A 4x 100nF 10 µF GND X5R λ LED1 POWER/ CONSOLE Vdd 58 RF0 6 RG8/AN18 CON8 26 10 AVdd Vdd Vdd Vdd CON5 17 COM3:RX MICROMITE I/O RESET TO IC1 PIN 7 SPI1 OUT (3) 8 12 (4) 14 (5) (9) (10) (14) (16) (17) COM2:TX 11 COM2:RX 13 SP1I IN 45 COUNT/WAKEUP/IR 51 I2C CLOCK 44 I C DATA 43 2 (18) RB6/AN6 SDA2/RF4 SCL2/RF5 RE0 RE1 AN20/RE2 RE3 AN21/RE4 RG9/AN19 RB4/AN4 RB2/AN2 59 COM1:RX (22) 24 (24) 50 SPI1 CLK (25) 27 (26) IC1 PIC3 2 MX470PIC32MX470F512H RD3/AN26 RD10 AN10/RB10 RD5 Vdd Vss 62 PWM 1C AN23/RE6 RB12/AN12 AN27/RE7 AN8/RB8 MCLR PWM 2A Q1 DMP2215L SCK Q2 2N7002 LED SDO (MISO) SPI2 CLK T_CLK 1 T_CS 5 SPI2 OUT T_DIN 47 SPI2 IN/PWM2B T_DO 3 T_IRQ 21 ILI9341-BASED TFT DISPLAY CON9 PMA7/RB9/AN9 OSC2 AVss Vss 40 20 9 Vss 25 Vss 41 22 CS Vcap MISO 56 SCK X1 20MHz 10 µF CON7 X5R 22pF 1 2 3 DI 3V3 4 SCK 5 GND 6 7 8 CS MOSI DO +3.3V PGD CON4 1 2 3 4 5 PROGRAMMING (ICSP) HEADER PIN NUMBERS IN RED INDICATE 5V TOLERANT INPUTS 20 1 6 PIN NUMBERS IN BLUE INDICATE ANALOG-CAPABLE INPUTS 10 µF X5R MICRO SD CARD SOCKET IC1 1 SC  CD PGC Vcc GND MCLR CARD DETECT OPTIONAL D/C SDI (MOSI) TO SD CARD SOCKET RB1/AN1/PGEC1 22pF RESET 2 RB0/AN0/PGED1 39 GND CS 53 4 SCK2/AN16/RG6 CON2 100nF VCC 10kΩ RD2/AN25 470Ω 63 64 COUNT RB11/AN11 IC2 MCP120-270 RST 61 23 RF1 OSC1 RESET S1 32 60 RD9 RC13 15 55 31 29 AN14/RB14 AN17/RG7 10kΩ 54 PS/2 KEYBOARD DATA 1kΩ +5V 7 30 +5V RD11 AN22/RE5 16 52 PS/2 KEYBOARD CLOCK RB3/AN3 GND +3.3V 28 CON3 +3.3V +5V 50 COUNT RB5/AN5 COM1:TX (21) 42 46 18 48 49 28 52 30 54 55 31 32 60 61 62 63 64 49 SPI1 CLK TO IC1 PIN 50 VUSB 3V3 RD8 RD0 RB7/AN7 SOSCO/RC14 AN24/RD1 AN13/RB13 RD4 AN15/RB15 RD6 RD7 INPUT ONLY 48 COUNT 35 57 38 34 VBUS 36 D– 37 D+ 33 RF3/USBID SB1 EXTRA I/Os 18 100nF 1 2 3 X 4 16 46 +3.3V 19 COM3:TX 45 PWM1A +3.3V MINI USB TYPE B 33 17 PWM2B/SPI1 IN 1k 10Ω JP1 17 TO IC1 PIN 45 8 COM3:RX TO IC1 PIN 17 K GND 42 SPI1 OUT TO IC1 PIN 8 ADDITIONAL I/Os REG1 MCP1703A-33E CON1 5V MICROMITE+ EXPLORE 64 CATHODE DOT MCP120 LED Vin GND RST A MCP1703 Vss K Vdd Vout Fig.1: the complete circuit diagram for the Micromite Plus LCD BackPack. It’s primarily composed of PIC32 micro­ controller IC1, which is programmed with the Micromite Plus firmware, plus connectors CON1-CON9 which give access to the I/O pins, interface with the touchscreen and provide the USB, serial and SD card interfaces. Mosfets Q1 & Q2 provide display backlight dimming while REG1 derives IC1’s 3.3V supply from the externally supplied, regulated 5V rail. Pin numbers shown in parentheses refer to the original LCD BackPack. nal from pin 53, the brighter the backlight. Commands to control the backlight will be shown later. The MCLR reset input of IC1 is held 68  Silicon Chip high by a 10kΩ pull-up resistor from the 3.3V rail, preventing spurious resets. The chip can be reset either by pressing onboard tactile pushbutton switch S1 or by pulling pin 1 of CON4 low. A 470Ω series resistor limits the current drawn from this pin when S1 is pressed. siliconchip.com.au X1 20MHz 22pF 22pF 10 µF 100nF 07110161 RevC = 5V tolerant GND RX TX 5V GND 5V 3V3 27 50 24 59 15 43 44 51 45 13 11 14 12 8 RESET 10kΩ CON3 Micromite+ LCD BackPack S1 1 10 µF 33 10 µF 1kΩ 1kΩ CON9 microSD K K 1 42 8 17 45 46 18 48 49 50 28 52 30 54 55 31 32 60 61 62 63 64 CON5 17 16 CON8 USB 100nF IC1 PIC32MX 470F 512H 10 µF CON2 CON4 ICSP SB1 100nF 1 SD CON8 10kΩ CON5 1617 16 1733 33 CON1 LED1 (ALTERNATIVE) 470Ω 100nF Q2 2N7002 Q1 DMP2215L 10Ω MCP1703A-3302E/DB CON3 REG1 TOUCHSCREEN SILICON CHIP LED1 © 2016 5V TX RX GND Vbus RESET 8 12 14 11 13 45 51 100nF 44 43 15 59 24 50 27 3V3 5V GND JP1 Reset (IC2) (1 00nF) (MCP120-270) CON4 ICSP S1 CON7 CON1 CON2 CON6 64 63 62 61 60 32 31 55 54 30 52 28 50 49 48 18 46 45 17 8 42 CON6 Fig.2: follow these top and bottom overlay diagrams to assemble the Micromite Plus LCD BackPack PCB. Most of the parts are SMDs and are fitted to the top side which later faces the rear of the attached LCD module. I/O connectors CON1, CON2, CON5 and CON6, along with in-circuit programming header CON4, are fitted to the other side. Reset switch S1, USB socket CON8 and microSD card socket CON9 are accessed via the edges of the module. Like the LCD BackPack and Explore 64, the Plus BackPack has provision for IC2, an MCP120 2.7V supply supervisor which will reset IC1 should the nominally 3.3V supply drop below 2.7V. Normally, this is not necessary, however it may prevent the unit from misbehaving in a harsh environment. If you want to fit the MCP120, the only other component you need is fit is its adjacent 100nF bypass capacitor. Power supply The unit is intended to be powered from an external regulated 5V supply. The acceptable voltage range is 4.55.5V which means that the USB port of a PC or a USB charger is quite suitable for powering the Plus BackPack, either via CON8 or flying leads connected between pins 1 and 4 of CON1. Current drain is up to 250mA with full brightness on the display backlight and the Micromite running at full speed. With the display backlight off, the supply current is more like 80mA and this can be reduced if the Micromite is in sleep mode or running at less than maximum speed. Note that you must not use an unregulated 5V supply as these can easily reach over 6V which is the threshold for damage to REG1 and possibly other components (eg, the display module). REG1 is a 250mA 3.3V low-dropout regulator which can deliver the rated 250mA with just 3.925V at the input. Its own supply current is just 2µA with a light load. It has 10µF input bypass and output filter capacitors. IC1 has five 100nF bypass capacitors, located near its five supply pins, siliconchip.com.au with a 10Ω resistor to help filter its analog supply (AVDD). Finally, LED1 indicates when power is present and is fed with around 1mA thanks to its 1kΩ series current limiting resistor. Note that pads are provided to mount LED1 on either side of the PCB, depending on your preference. PCB design The Micromite Plus LCD BackPack is built on a double-sided PCB measuring 86 x 50mm which is identical to the size of the original Micromite LCD BackPack. Most of the components are on one side, which ends up facing the back of the display module. Fig.2 shows the details. Besides routing all the tracks from IC1 to the various connectors, our main goal was to keep high-speed signals separated to prevent cross-talk and to provide a low-resistance ground plane across the whole board to minimise EMI and inductive coupling between tracks. As such, it is studded with numerous vias between the top and bottom layer ground planes, including many under IC1. CON3 and CON7 are located to plug straight into the display module and the four mounting holes are spaced to suit that module too. CON1, CON2 and CON6 can either be mounted on the back of the module or on the display side but using right-angle headers. CON5 can be left off in most cases and if you only need a few I/O pins, you don’t need to fit CON6 either. The microSD card socket, CON9, is best used for permanent storage such as graphics or program data; it may be possible to design a case to allow access to insert and remove this card from outside but it would be difficult. This would be easier to arrange with the SD card socket on the display module, as the larger full-size SD card protrudes much further. CON4 would normally be fitted as a right-angle header on the bottom of the board as shown on Fig.2, to reduce the overall height of the module, although there’s nothing stopping you from using a straight header should you wish. CON8 and S1 are easily accessed from the side of the module, despite being mounted between the two boards, although note that a cable plugged into CON8 may interfere with plugging a PICkit 3 into CON4 if using a rightangle header. Should you wish to mount some sort of “shield” on the back of the BackPack module (like we did in the Touchscreen Voltage/Current Reference in next month’s issue), the four mounting positions can be used to attach spacers on either side of the board. Construction Construction is quite similar to the Micromite Plus Explore 64 as we are using mostly the same parts. The only slightly tricky components to fit are IC1, CON8 and CON9 as these have relatively close pin spacings. The other components either have wide spacings or are conventional throughhole types. The essential tools are a good magnifier, plenty of flux and a steady hand. The magnifier needs to be at least x3 power and preferably x10. A jeweller’s November 2016  69 The Micromite Backpack PCB plugs directly into a 2.8-inch LCD. Note that this view shows a prototype PCB; the ICSP header (if used) goes on the other side of the PCB in the final version and there are other minor differences. loupe can be used but the best option is a stereo microscope and SILICON CHIP reviewed some good candidates in the July 2014 and November 2015 issues. The flux should be a good quality flux paste/gel such as Cat. H1650A from Altronics or Cat. NS3036 from Jaycar. Fig.2 shows the parts layout on the Plus BackPack PCB. The first step is to install microcontroller IC1. Apply flux to all of its pads, then position the chip so that its pin 1 (marked with a dimple) is lined up with the pin 1 marking on the PCB. Then hold it in position using a toothpick or tweezers and solder one corner pin. An alternative technique is to first apply solder to one pad, then heat the solder on that pad while quickly sliding the IC into place, after which you lift the iron off the board. This requires more practice but you can make several attempts, as long as you avoid spreading the solder onto adjacent pins. Now check that the IC is correctly aligned; if not, re-melt the solder while gently nudging it into position. Once it’s in position, apply more flux to all the pins and solder each one in turn, then recheck the first pin and add fresh solder if necessary. The technique here is simple; put a very small amount of solder on your iron’s tip, touch the tip to the solder pad and slide it forwards to gently touch the first pin. The solder should 70  Silicon Chip freely flow around the pin and the pad. You should then be able to solder at least 15 more pins (one side of the IC) before you need to add more solder to the iron. The secret is to be generous with the flux, as this will allow the solder to flow freely onto the pads and their corresponding pins. Alternatively, if you have a mini-wave tip or a very steady hand, with sufficient flux in place, you can drag solder across one side (16 pins) in a single movement. Often you will find that you are actually soldering two or more pins simultaneously but the solder will not usually bridge the pins. If it does, this is an indication that you have too much solder on your iron. If any pins are bridged, come back later with solder wick (and more flux) and remove the excess. The SD card connector is next on the list. It’s located on the PCB by two small plastic pins that match two holes on the board. Solder its four mounting lugs first, followed by the signal pins. These pins are soldered using the same technique as for IC1. Note that the SD card connector’s pins are fragile and the plastic they are embedded in will melt if too much heat is applied, so only touch the soldering iron to the pins for a very short time. As before, apply plenty of flux before soldering. The mini USB connector can now go in. It also has locating pins to position it correctly. You may have to push it down firmly for it to sit flush with the board. Once again, solder the mounting lugs first and then the signal pins. These are a bit of a challenge as they are partially under the connector’s body and you will need a fine-tipped soldering bit to reach them; we have extended the pads outside the body to make this easier. You can now solder REG1 in place. This has a large tab which connects to the copper ground plane on the PCB. Start by applying flux to all four pads, then slide it into place and solder one of the smaller leads before checking the positioning. Once you’re happy, solder the other smaller leads and finally the large tab. It may take a few seconds to heat the part and PCB up enough to get a good solder joint on that tab. Follow with small Mosfets Q1 and Q2. These devices have wide pin spacings and heat up quite fast, so you should have them in place pretty quickly. If fitting the optional supply supervisor, IC2, which also comes in an SOT-23 package, whack that on now as well. Passive SMD components Soldering the passive SMD components requires a slightly different technique. Start by applying flux to one solder pad and then tin it by applying a thin layer of solder to it. That done, you have two choices. First, you can place the component in position and hold it still with a toothpick or tweezers while you apply the iron’s tip to the end sitting on the tinned pad and the component lead will sink into the solder underneath. Alternatively, you can slide the component into place while heating the solder on the pad. The second technique will probably require more practice but it may be quicker once you get used to it. Either way, once the component is secure, apply more flux and solder the other end before returning to the first to make sure that the joint is good. Once again, the secret is to use plenty of flux and don’t forget that it may have boiled off one of the pads while you were soldering the other end of the component, so keep reapplying it. Solder the six resistors and 12 capacitors using this method. LED1 (the power indicator LED) is the last SMD to be fitted. This device siliconchip.com.au USB USB-To-Serial Converter Micromite Plus BackPack PCB Fig.3: the Micromite LCD BackPack is connected to your PC using a USB-toserial converter. All programming and control of the Micromite is carried out via the console using a terminal emulator on the PC. Once the program is debugged and running, you can then disconnect the USB-to-serial converter. is polarised and should be marked with a bar or dot on the cathode end. Some LEDs might be different so it is a good practice to use a multimeter’s diode test facility to check the polarity. Solder it in place with the cathode towards the top edge of the board, as shown in Fig.2. It’s up to you whether to put it on the same side of the board as the other SMDs, where it will ultimately face towards the front of the unit (ie, aimed at the back of the TFT module) or on the other side, where it will be more visible but facing the back of the unit. Through-hole components Install crystal X1 using the usual method. PCBs supplied by SILICON CHIP will have solder mask over the top side of the mounting pads so it should be possible to push the crystal can right down onto the PCB surface before soldering it. Next comes tactile pushbutton S1, which is soldered into place with its actuator sticking out (barely) over the edge of the PCB. Push its pins all the way down before soldering them. Now you can solder headers CON3 and CON7 in place, on the same side as the other components. You may find it best to temporarily plug in the TFT module and attach it using the tapped spacers to ensure these are positioned correctly. Now you can solder CON1, CON2 and optionally CON4, CON5 & CON6 to the opposite side of the PCB. Make sure they’re all straight and flat on the board before soldering more than two pins. JP1 can go on either side of the board. We’ve shown it on the side that will face the TFT module but this does siliconchip.com.au make it difficult to change when the display module is in place (which may or may not be a good thing). Finally, it’s time to attach the TFT module. Use M3 x 6mm machine screws to attach M3 x 12mm tapped spacers to each mounting hole, with the spacers on the same side as CON3 and CON7. Then plug the module into both CON3 and CON7 (noting that you’ll need to fit the 4-pin male header on the TFT module, as it comes without it). Attach the module to the spacers using the slightly longer machine screws, with the Nylon washers under each screw head. These will be used as spacers later if you decide to attach the whole thing to the lid of a box or case. Loading the firmware Programmed PIC32s are available from the SILICON CHIP Online Shop and will be supplied with any Micromite Plus LCD BackPack kits purchased. If using a blank PIC32 chip, you will need to program it yourself. In this case, you will need a suitable programmer such as a PICkit 3 from Microchip. This can be used to program IC1 via CON4. The first step is to download the firmware from the SILICON CHIP website and extract the Micromite Plus hex file (ie, the firmware). It’s then just a matter of using your computer and the MPLAB software supplied with the PICkit 3 (or downloaded from Microchip) to program the hex file into the microcontroller; see page 26 of the February 2016 issue for further details. During this procedure, the PICkit 3 will verify the programming operation by reading back the data on the chip. If it reports a fault, you will need to fix that before progressing. Usually, though, the programming operation will be verified as OK, indicating that the PIC32 has been correctly programmed. Serial console To set up and use the Plus BackPack, you must connect a terminal emulator to its console. The console is a serial interface over which you can issue commands to MMBasic to configure the chip and edit or run programs. MMBasic also uses the console to display error messages. As mentioned earlier, the Plus BackPack actually has two consoles, one serial and one USB. A USB-to-serial converter is required in order to use the hard-wired serial console. One end of this converter plugs into a USB port on your computer, while the other end connects to the Micromite’s serial console – see Fig.3. To your computer, it will look like a serial port (via USB), while the connection to the Micromite Plus is a standard serial interface with TTL (0-3.3V) signals levels. JP1 must be installed if you want to power the Plus BackPack via CON8. However, it must NOT be fitted if you are powering the unit externally and if there’s any chance you will use CON8 to access the USB console. So check whether your fitting of JP1 is correct before proceeding. We recommend converters based on the CP2102 chip. These are available from the SILICON CHIP online shop at www.siliconchip.com.au/ Shop/7/3437 They are each supplied with a short DuPont female/female cable which plugs straight into the Plus BackPack board. Fig.3 shows how a CP2102-based November 2016  71 ner). This can be done using a logic probe, oscilloscope or, at a pinch, a moving coil multimeter. If you do see some activity, the fault is probably either an incorrect console connection or is in the USB-to-serial converter. User manuals Connectors CON1 & CON2 are mounted on the rear of the Backpack PCB as shown in the photo. CON4 & CON5 also go on this side of the board in the final version – see Fig.2. converter is connected to the BackPack (other types should be similar). Note that the converter feeds through the 5V supply rail derived from the PC’s USB port to power the Plus BackPack. When the converter is plugged into your computer and the correct driver is installed, it will appear as a serial port (eg, COM3 in Windows). You then need to start a terminal emulator on your computer. For Windows, we recommend Tera Term V4.88 which can be downloaded for free from http:// tera-term.en.lo4d.com You will need to set its interface speed to 38,400 baud and connect it to the serial port created by the USB-to-serial converter. Once that’s been done, hit the Enter key in the terminal emulator and you should see the Micromite’s prompt (“>”) – Fig.4. You can then enter, edit and run programs from the command prompt using nothing more than the terminal emulator and a USB cable. Testing If you don’t see the Micromite’s prompt, something is definitely wrong and you will need to go through the following troubleshooting procedure. The first step is to measure the current drawn by the Plus BackPack from the 5V power supply. With nothing attached to its I/O pins, this should be 60-80mA. If it is substantially more or less than this, it indicates that something is wrong with either the soldering, the microcontroller or its power supply. If this is the case, check that +3.3V is present on pins 10, 26, 38, 57 & 35 of 72  Silicon Chip IC1 and on various other components – see Fig.1. If this checks out, check that the capacitor connected to pin 56 (Vcap) of IC1 is correctly soldered and is the correct type; it must be a 10µF multi-layer ceramic type. A faulty capacitor will prevent the internal CPU from running and the current drain will be quite low (less than 10mA). A disconnected pin can also prevent the micro from running, so check the soldering on IC1’s pins. It’s easy to miss a pin and leave it floating just above its solder pad and without a decent magnifier and bright light, this may not be obvious. Another cause of low current drain is either not programming the Micromite Plus firmware into the chip or ignoring an error during this operation. Check that the micro has been correctly programmed. If the current drain is about right, the next step is to attach the Plus BackPack console to your computer or terminal emulator as shown in Fig.3. You could also try using the USB connector as the console. With the console connected, press the Reset button on the BackPack and you should see the start-up banner as shown in Fig.4. Note that you will not see this banner if you are using the USB console because resetting the Plus BackPack will also reset the USB interface. If you don’t see the start-up banner you should check the console Tx pin for some activity when the Reset button is pressed (this indicates that MMBasic is outputting its start-up ban- The Micromite Plus is quite an advanced device. After all, it is a full computer with a multitude of facilities. As a result, it has two user manuals which together add up to almost 200 pages. The first manual is called the “Micromite User Manual” and it describes the features that are standard across the whole Micromite range, from the original 28-pin version to the 100-pin Micromite Plus (featured in the September & October 2016 issues). The extra features of the Micromite Plus are described in the “Micromite Plus Addendum” which covers subjects such as the GUI functions, the SD card interface and other features that are only found in the Micromite Plus. Both manuals are in PDF format and available for free download from the SILICON CHIP website. Before you build and test the Plus BackPack, it would be worthwhile downloading and looking through them as they provide a lot more information than we can fit into these pages. Configuring the display While MMBasic for the Micromite Plus has inbuilt support for 10 different LCD panels, the Plus BackPack is specifically designed to attach to the 2.8-inch diagonal 320x240 display with an ILI9341 controller. For details on how to connect it to other types of display, see the Explore 64 article in the August 2016 issue (pages 70 & 71). Before configuring the display, you need to turn the backlight on or else it will be very difficult to see anything. Do this using the following command: PWM 2, 1000, 50 This sets the brightness to 50% (approximately). You can adjust this value later if required. Assuming you can see that the backlight is now on, proceed to configure the display as follows: OPTION LCDPANEL ILI9341, L, 2, 23, 29 To test the display, enter the command: GUI TEST LCDPANEL siliconchip.com.au You should immediately see an animated display of colour circles being rapidly drawn on top of each other. Pressing the space bar on the console’s keyboard stops the test. Note that once the display has been configured, you don’t need to do it again as the configuration options are stored in the micro’s flash memory. Configuring touch Once the LCD panel has been configured, you can set up touch sensing using the following command: OPTION TOUCH 1, 3 If you have connected a piezo buzzer to one of the unit’s pins via a driving transistor and want this buzzer to click when the screen is touched, you can add this pin number onto the end of the command (with a comma separating it from the final digit). As with other options, this command only needs to be run once and every time the Micromite is restarted, MMBasic will automatically initialise the touch controller. If the touch facility is no longer required, the command OPTION TOUCH DISABLE can be used to disable the touch feature and return the I/O pins for general use. Before the touch facility can be used, it must be calibrated using the GUI CALIBRATE command. The calibration process starts with MM­Basic displaying a target in the top-left corner of the screen. A blunt, pointed object such as a stylus is then pressed exactly in the centre of the target and held down for at least one second. MMBasic will record this location and then continue the calibration by sequentially displaying the target in the other three corners of the screen. Following calibration, you can test the touch facility using the GUI TEST TOUCH command which will blank the screen and wait for a touch. When the screen is touched with a stylus, a white dot will appear on the display. If the calibration was carried out successfully, this dot will be displayed exactly under the location of the stylus. Pressing the space bar on the console’s keyboard exits the test routine. Configuring an SD card Now that you’ve set up the display and touch interfaces, you can configure it to use an SD card. Assuming you have fitted CON7 and the matching header on the TFT module, you can siliconchip.com.au plug a full-size SD card into the socket on the back of the display. Whether or not you have done this, you also have the option of plugging a microSD card into the onboard socket. You can’t use both at the same time, though. We would have liked to provide separate CS lines so that both sockets could be used however the Micromite Plus software requires a reboot to change the CS pin, making this impractical. So for now, they are connected in parallel and only one can be used at a time. Before plugging in the card, you need to run the OPTION SDCARD command. Note that this must be entered at the command prompt and can not be used in a program. To set up the microSD card socket, use: OPTION SDCARD 21, 22 or for the full-size card socket: OPTION SDCARD 21 Unfortunately, the TFT module does not break out the card detect pin on the full-size socket, so you can’t change the card while the unit is running. After running either command, you will need to restart the Plus BackPack (eg, with reset button S1). After that, MMBasic will automatically initialise the SD card interface each time. SD card not required If the SD card is no longer required, the command OPTION SDCARD DISABLE can be used which will disable the SD card and return the I/O pins for general use. To verify the configuration, you can use the command OPTION LIST to list all options that have been set, including the configuration of the SD card. As another test, you can pop an SD card into the slot and run the command FILES. This will list all the files and directories on the card. Note that some SD cards can be temperamental and may not work so if you encounter a problem here, try a few SD cards before deciding that you have a fault. For example, some cards (especially high capacity, fast types) may demand more current than the power supply on the Plus BackPack can provide. USB interface The USB interface on the Plus BackPack doesn’t need configuring. MMBasic monitors the interface and if it de- Fig.4: this is what you should see in your terminal emulator when you press the reset button on the Micromite Plus LCD BackPack. If you don’t see this, the probable reason is that the USB-serial converter is not connected correctly. tects a host computer, it will automatically configure it for serial emulation over USB. A Windows-based host computer (versions before Windows 10) will require the installation of the “SILICON CHIP Serial Port Driver”, which can be downloaded from the SILICON CHIP website. Macintosh and Linux based computers do not need a device driver, as support is built into the operating system. Windows 10 should not require any drivers to be installed. Once configured, the USB interface works just like a serial port that’s connected to the console. You can start up a terminal emulator such as Tera Term for Windows and tell it to connect to the virtual serial port created by the Micromite Plus. Anything outputted by the Micromite Plus will be sent out on both the USB interface and the serial console. Similarly, anything received on either of these interfaces will be sent to MMBasic. One benefit of using the USB interface as the console is that you can disable the serial console. This allows you to use the I/O pins allocated to the serial console for other duties, including use as a fourth serial I/O port. This is described further in the “Micromite Plus Addendum”. Further details We’re publishing further information on how to use the graphics, GUI, SD card and touch functions of the Micromite Plus in two feature articles, one in this month’s issue (p58-62) and the second in next month’s issue. For further details, refer to the Micromite user manual and addendum, available for free download from the SILICON CHIP website, Geoff Graham’s website at http://geoffg.net and The Back Shed forum at www.thebackshed.com SC November 2016  73