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The PicoPi Pro Robot Here’s one for kids from 7 to 77; whether a raw beginner or a dab hand! It’s a small, two-wheeled robot which you put together from a kit, then program to perform a variety of tasks. For example, you can get it to follow lines, detect edges, play music and much more. They’ll “learn by doing” using a visual programming language and an inbuilt LCD screen. It’s a great school holiday project but will keep them entertained all year! Play complex musical tunes with the piezo buzzer It can be up and running within a day of work 8-bit PWM motor speed control (0-255 steps) In-circuit programming with visual programming language Powered from four AA cells Line, edge and wall detection By Bao Smith Good for beginners to electronics Can move in eight directions = 86 86  S Silicon Chip Australia's Australia’s electronics magazine siliconchip.com.au T o build the PicoPi Pro robot, you need to do some basic soldering, a little bit of mechanical assembly and some simple programming. It is a good project for children 7-8 years and older. This kit would make a good gift for someone who wants to get into microcontrollers and robotics but doesn’t want to learn C/C++ or Python programming languages (as would typically be used with an Arduino or Raspberry Pi-based robot). It consists of about seven different modules which can be built separately and then combined to form the final robot. The total cost is $110.00 (or $93.50 without the LCD module) and it can be built and running within a day. You’ll need a soldering iron, side cutters, glue, Blu Tack, four AA cells and a programming cable. The micro is supplied pre-programmed, but you need to use a programming cable to load software onto the robot so it can perform different actions. The latest version of the kit can be programmed using a PICkit 3 or sim- Parts List 1 circular piece of laser-cut acrylic, 125mm diameter 2 wheels with rubber tyres 12 M3 x 10mm plastic pins 12 M3 x 10mm screws 8 M3 hex nuts 2 velcro strips 2 metal gear 300rpm motors with semi-D shafts 2 motor housings 1 plastic case for the driver module 1 large steel bearing ball & housing 1 16x2 backlit serial LCD module 1 3-wire cable with plugs at each end Driver module 1 driver PCB, 45 x 28mm 1 PIC16F506-E/P microcontroller 1 L293D motor driver IC 1 1N4148 small signal diode 1 1µF 25V tantalum capacitor 1 180kW resistor 1 4 x AA battery holder 1 2.5mm jack socket 1 16-pin DIL IC socket 1 14-pin DIL IC socket 1 3-way screw terminal block 1 3x7-pin header 2 4-pin header siliconchip.com.au ilar via a 5-pin male header, and we would recommend that you take that approach since you will then have a programming tool that’s suitable for other uses. The slightly older version of the kit that we built is instead programmed using a proprietary USB programmer that connects to a 2.5mm 4-pole jack socket on the robot. This programmer costs $26.40 as a kit or $41.03 pre-made. Either way, the programming is done “in-circuit” (ie, with the robot completely assembled), making it easy to experiment with the robot. Building the modules All the parts come organised in individual bags, as separated in the parts list. You will need a soldering iron with a fine-tip and a Phillips head screwdriver, plus a pair of side cutters to trim the leads after soldering the components. When soldering, it’s generally best to start with the items that have the shortest pins or pin spacings, as these are more difficult to solder if the board is already partially populated. Polarised components Some components are polarised and it does matter which way around they are placed in the circuit. This includes the one diode, the LEDs, the tantalum capacitors and the ICs. The diode has a black stripe at one end marking its cathode and this is lined up with the white stripe printed on the PCB where it is soldered. Each LED has one shorter and one longer lead. The longer lead is the anode (+), and the shorter lead the cathode (-). Make sure the cathode goes to the square hole on the PCB. Make sure the notch on both the IC socket and the IC matches what’s shown on the PCB. The tantalum capacitors are polarised and will be printed with a stripe on the body, indicating the positive lead (which may also be longer). So when fitting these capacitors, the positive lead goes into the pad closest to the positive symbol printed on the PCB. When soldering the components to the PCBs (printed circuit boards), many of them are not polarised and so it does not matter which way around you place them. All components listed here are included in the PicoPi Pro Robot Kit, available from PicoKit (www.picokit.com.au; phone (07) 5530 3095), for $110 inc GST and P&P 1 3-pin header 1 jumper shunt Microswitch modules (makes two) 2 microswitch PCBs, 20 x 11mm 2 snap-action microswitches 2 10kW resistors 2 3-pin right-angle headers 2 3-wire cables with plugs at each end Photodiode & IR LED modules (two) 2 photodiode sensor PCBs, 20 x 20mm 2 3mm photodiode sensors 2 3mm infrared LEDs (940nm) 2 photodiode/LED plastic holders 2 330W resistors 2 10kW resistors 2 3-pin right-angle headers 2 3-wire cables with plugs at each end Pushbutton modules (two) 2 pushbutton PCBs, 20 x 20mm 2 12mm tactile pushbutton switches 2 10kW resistors 2 3-pin right-angle header 2 3-wire cables with plugs at each end Australia’s electronics magazine Potentiometer module 1 potentiometer PCB, 20 x 20mm 1 50kW linear potentiometer & knob 1 3-pin right-angle header 1 3-wire cable with plugs at each end Buzzer module 1 buzzer PCB, 25 x 25mm 1 17mm piezo buzzer 1 BC327 PNP transistor 1 2.2µF 16V tantalum capacitor 1 10kW resistor 2 4.7kW resistors 1 3-pin right-angle header 1 3-wire cable with plugs at each end LED cables (two) 1 5mm blue LED 1 5mm red LED 2 180W resistors 2 2-wire cables with plugs at each end You will also need the PicoFlow USB programmer, PICkit or similar, four 1.5V AA cells, glue and/or Blu Tack. January 2019  87 Building the robot Step 1: assemble the driver module, fitting the parts where shown on the PCB. Step 2: assemble the two microswitch modules, fitting the parts where shown on the PCB. The microswitches mount on the edges of the two boards. Step 3: assemble the two photodiode/IR LED modules, fitting the parts where shown on the PCB. Feed the photodiode and LED pairs through the plastic mounting blocks and ensure the LED orientation is correct before soldering them to the PCBs. Step 4: assemble the two pushbutton modules, fitting the parts where shown on the PCB. Step 5: assemble the potentiometer module, fitting the parts where shown on the PCB. Step 6: assemble the buzzer module, fitting the parts where shown on the PCB. Step 7: assemble the two LED cables. Cut one of the leads of each cable in half. Then strip 5mm of insulation off the wires. Then trim the leads of the supplied 180W resistors short and solder them to the exposed ends of the wire (as shown below). 88 Silicon Chip You will end up with two cables with resistors soldered into the middle of one of the wires. Twist the wires together and plug the LEDs into one end of the cable, with the shorter lead (negative) going to the wire you soldered the resistor onto. You can trim the LEDs leads if you want, but make a note which lead is the negative (cathode). Step 8: peel the protective film off both sides of the laser-cut circular acrylic base. Step 9: attach the driver module to its open plastic case, using two short (~4mm) self-tapping screws. Step 9: attach the driver module (in its case) to the middle row on the base, using two short M3 machine screws and nuts. The notch for the programming socket should be seated near the outer rim of the acrylic base. Step 10: take the spare 2-wire cable and cut it in half, then remove the insulation to expose about 5mm of wire. Heat and apply a small amount of solder on the ends of the wire (tin them) and then push them through the holes in the tabs on the back of the motor and solder them in place. Do this for both motors. When soldering apply heat for only a short period, so that the soldering iron doesn’t burn the plastic on the motor. A pair of side cutters is the safest way to cut the off the end of the motor housing. The motor should fit tightly in the housing, otherwise use a file to widen it slightly. Step 11: the plastic motor housings supplied are a bit small to fit the motors. Use side cutters to completely open up the rear of each housing, where the vertical slot is located (see photo above). That will give enough room for the rear of the motor to fit and for the motor wires to poke out. Once you’ve cut the unnecessary plastic out, you can use sandpaper or a small file to smooth the edges and widen the motor housing slightly. Step 12: place the rubber tyres over the two wheels and then push the wheels onto the motor shafts. Step 13: place the motor into the housing so that it fits flush. You might need to force the motor in to get it to fit. Apply a small amount of silicone sealant or glue to the wires so that they are attached to the inside of the housing, preventing the wires from moving around and breaking the solder joints. Step 14: attach the completed motor housing to the base using two screws and nuts each. The wheels fit through the wide slots near the edges (see photos). Step 15: attach the leads from the two motors to the headers on the driver module labelled M1 (left wheel) and M2 (right wheel). Don’t worry about the orientation at this stage, since if one wheel runs backwards, you can easily swap them around later. Australia’s electronics magazine siliconchip.com.au Step 16: push four of the plastic pins into the holes around to outer rim of the base so that the photodiode & IR LED modules can be attached to the underside, as shown in the photo below. We suggest you attach the two modules close to the driver module with the pin headers facing inwards, as we did. Step 21: attach the ball housing to the underside of the base, opposite the driver module, using two screws and nuts (see photo below). Step 22: attach the two microswitch modules to the underside of the base, one on each side of the bearing ball, using two screws each. Note the orientation of the switches in our photos. The switch levers should face towards the centre. Step 23: now everything can be wired up to the headers on the driver module. Fig.1 shows where each lead Step 17: using four more plastic pins, attach the two pushbutton modules on the top side of the base, near the wheels, facing inwards. You will need to bend the pin headers up slightly so there is enough space to plug the connecting leads on later (see below). Step 18: attach the buzzer module on the opposite side of the right-hand wheel using two more plastic pins, as shown in our photos. Step 19: attach the potentiometer module, on the opposite side to the buzzer module (behind the left wheel), using the same method. Step 20: push the steel bearing ball into the supplied housing (as shown directly right) as it provides extra support for the robot. It should be held in with friction. siliconchip.com.au Australia’s electronics magazine January 2019  89 goes and also indicates the wire colour which should go to each pin. Start by wiring up the buzzer, pushbuttons, potentiometer, LCD, LEDs and motor connections. Note that you will almost certainly end up with a mass of wires above the driver module. It can’t really be avoided (see photo below). In each case where there is a 3-wire lead to plug into a separate board, plug it in with the yellow wire closest to the square mark on that board. The exception is the photodiode/IR LED modules, where the yellow wire goes to the pin marked J2. To keep the wiring relatively neat, it’s a good idea to feed the leads between the two motor housings and pull the loose ends back towards the bearing ball end of the base. Note that two of the 3-wire leads pass from the top side of the robot to the bottom, through the slots, and connect to either the photodiode/IR LED modules or the microswitch modules, Fig.1: connection diagram for the PicoPi Pro Robot. Note the colour code on the seven 3-pin headers as they must match with the provided wires. The 36V connection is not used here – it’s only used to power larger motors. or a combination of the two, depending on which you want to use. Step 24: determine how you will mount the battery holder so that you can access the on/off switch, replace cells and fit the LCD screen. We attached the battery holder to the top of the two motor housings using a stick of Blu Tack split in half to create two rectangular stacks (see lead photo). The LCD screen is then attached to the front of the battery holder using the supplied velcro strips. I arranged it so that the power switch was facing up and next to the potentiometer module. You may be able to attach the battery holder using velcro as well; it all comes down to how your wiring is arranged. A more attractive method might be to cut two small wedge-shaped pieces of timber of around 15mm x 15mm, with a height varying between about 10mm and 13mm. These could then be glued to the top of the motor housings, with velcro glued on top of the timber strips, to attach the battery holder. Step 25: glue velcro to the back of the LCD module and glue the matching piece to the battery holder. You may find that bending the 3-pin header on the LCD module makes attaching the wire lead easier. Plug the other end of the wire onto the driver module as shown in Fig.1. Step 26: before attaching the battery holder, connect the red and black wires from the battery pack to the screw terminals on the driver board. As shown in Fig.1, the red wire goes to the terminal next to the jumper (6V), while the black wire goes to the middle terminal (GND). Step 27: place the jumper shunt on the 3-way pin header next to the screw terminals, in the position closest to the nearby IC. This selects low-voltage (ie, battery) operation. Step 28: insert four AA cells into the battery holder, making sure it’s switched off beforehand. Then attach the battery holder to the PicoPi Pro Robot. We found with our battery holder that it took quite a bit of force initially to get it to switch on properly. Be sure to give it a strong push if the LCD doesn’t light up. Step 29: the two LED cables are optional. You can place the LEDs wherever you want to. If fitting them, plug the wires side-by-side into the 4-pin header next to the programming interface on the driver module, with the polarity shown in Fig.1 (if they don’t work when you try them later, it’s easy to reverse the plugs). The Robot assembly is now complete and it’s time to program it to do something useful! Programming The PicoFlow USB programmer from PicoKit plugs into a spare USB What does each module do? Driver module – powers and controls all the other modules via digital and analog signals. Also controls motor speed and direction. Microswitch module – detects when the Robot bumps into something. Photodiode & IR LED module – detects whether the surface beneath the sensor is light or dark. This allows the unit to pick up and follow dark lines beneath it. Pushbutton module – gives you a way to control the Robot directly, eg, start or stop a program or manually move it in one direction or another. Potentiometer module – can control the motor duty cycle via PWM (or some other parameter in your program). Buzzer module – can be used to play sounds/music. LED cables – use the red and blue LED to indicate status, as headlights or just to make the Robot look nice. LCD module – displays debugging details and text. Resistor Colour Codes 90 Silicon Chip No. Value 4-Band Code (1%) o 7 10kΩ brown black orange brown o 2 4.7kΩ yellow violet red brown o 2 330Ω orange orange brown brown Australia’s magazine o 2 180Ωelectronics brown grey brown brown 5-Band Code (1%) brown black black red brown yellow violet black brown brown orange orange black black brown brown grey blacksiliconchip.com.au black brown port and is supplied with a 4-pole 2.5mm jack cable which plugs straight into the driver board and allows you to reprogram the onboard micro directly from their PicoFlow Alpha visual programming software. If you have the later version of the PicoPi Pro Robot with the 5-pin programming header, and a suitable programmer like the PICkit 3, you don’t need the PicoFlow programmer. The PicoFlow Alpha software is available for Windows only and can be used for free for two years. You can download it from the link at the bottom of this web page: siliconchip.com. au/link/aamb Once you have installed this software, launch it and we are ready to write our first program. It’s best to start with something basic. For example, one which sets the micro’s output pins to a static state which causes the motors to run, eg, causing the Robot to rotate in place. Having launched the PicoFlow Alpha software, double-click on the “output tool” (which looks like a blue microcontroller). A window will appear, as shown in Screen 1. This lets you set the pins to a high or low state. Screen 1 shows the simplest example program you can run on the PicoPi Pro Robot. The program has just two elements, the “Start” tool, which looks like a traffic light, and the “Dig- The PicoFlow USB programmer will need to be used to program the PicoKit if your robot only has a 2.5mm socket. Otherwise, you can use a PICkit 3 or similar. ital Output” tool, which looks like a microcontroller. Drag and drop components from the left-hand pane to the central pane to create this program. Then doubleclick on the Digital Output tool to set the output states. In our example, we have pin C4 set to high which causes the left wheel to rotate forward, making the PicoPi Pro Robot move in a circle. The motor control pins are as follows: C3 high – right wheel forward B5 high – right wheel back C4 high – left wheel forward C5 high – left wheel back Leave all the other pins in a low state. For example, setting C3 and C5 both to high will make the Robot rotate in-place. Once you’ve finished setting up the output states, make sure that its “output” is fed back into itself so that the program will keep the outputs in that state forever. You can right-click on the Assembly Code tab at the top of the window to export the program as an ASM or HEX file, but note that the HEX files produced by this program cannot be read by MPLAB IPE. So you will need to use PicoFlow Alpha’s programming support to upload code to the microcontroller. You can do this by pressing the big Program button at the top of the screen. Make sure that the right type of microcontroller is selected in the dropdown box; it should be set to “14 Digital 16F505” or “14 Analog 16F506”. The Robot also needs to be powered up before programming. Make sure that Screen 1: This is the simplest program you can use with the PicoKit. All it does is move the left wheel forward (C4 high). Make sure that on the Programming menu the value selected is “14 Digital 16F505” or “14 Analog 16F506”. siliconchip.com.au Australia’s electronics magazine January 2019  91 all the leads are connected securely as intermittent connections can stall the programmer. Note that the photodiode/IR LED modules can potentially interfere when programming, unplug them before you start programming. If you’re having trouble getting it to program correctly (freezes, fails or takes too long), try putting some pressure on the connection between the programmer and the board. We found that the 2.5mm jack plug didn’t always make good contact with the socket and we had to hold it in to get the programming to work reliably. You should see the LED on the programmer rapidly flash while it does its job, which takes a few seconds. If it’s still going after 10 seconds, then something is wrong. The Music Editor can be accessed by clicking on Edit Music within a Sound tool. You can put notes into by selecting them as shown above, or you can load a musicXML file found online. A more advanced program Delay Tool (hourglass). Again, by double-clicking it, you’ll bring up a menu where you can set a time and units (from microseconds to years). We chose two seconds for our delay. Next, you need to place a Digital Output Tool to control the motors. Set C3 and C4 high similarly to how we did it in the previous example. That should make the Robot drive forwards (assuming its motors are wired up with the correct polarity). Add another Delay Tool (say about half a second), then use another Digital Output tool to bring those same two pins back to a low state. Create a final Digital Output Tool and connect this to the Sound Tool. Once again, double-click the icon and then go to the music sub-menu. This uses musical notation to determine the sound played on the piezo buzzer using a square wave. There are quite a few options you can fiddle around with if you are musically inclined, to create reasonably lengthy sequences of notes. It accepts musicXML files, so you can find sheet music online and load it up in this software to replay on the Once you’ve gotten the Robot to move, you can move on to some more advanced programs that take advantage of the different features of the PicoPi Pro Robot. Next, we’ll write a program that writes to the LCD screen, drives both motors forward, stops, plays a small tune on the buzzer and then restarts the motors again and repeats. First, we need a plain Start tool. Then, we create a Comms Tool (it looks like a serial port). Double-click on it and set it to transmit mode. Then go into the transmit sub-menu, set the source to literal, data-type to DEC (decimal) and value to 1. Most importantly, the size needs to be set to 9 bits and make sure the output pin selected is B4 (the pin connecting the LCD screen). That step clears the LCD screen before any text is written to it. Next, we create another Comms Tool set to transmit, but this time we set the source to text and again the output pin is B4. Here, you can enter whatever message you want to display, up to 32 characters long. Next, we use a 1-2 3 4 Silicon Chip More experimentation This Robot sample program and several others are available as a free download from the Silicon Chip website. Some of them take advantage of the infrared sensors on the front of the Robot to allow it to follow a black line. There’s also a program that will move a motor depending on which of the two pushbutton switches are pressed. You should be able to load each program, see how it works and start changing individual parts to see what does what. You can then start to modify your own, more advanced programs or even create them from scratch. Where to buy it The PicoPi Pro Robot kit is available for $110 from: www.picokit.com. au/Store/index.php?route=product/ product&path=2&product_id=122 You will need to make an account to view prices and make orders. Otherwise, you can contact them via telephone at (07) 5530 3095. 5 This shows the complete advanced program, which is available for free from the Silicon Chip website with a few other example programs. Use the screenshots shown at right to complete each major step of the program. 92 buzzer. The sound tool is fairly powerful, but it would help to know how to read sheet music. Australia’s electronics magazine 6 siliconchip.com.au 1 2 Connect the Start tool to the input of a Comms Tool, double click the Comms Tool and set it to transmit (left). Then in its transmit submenu (right) the source should be set to literal, data type to DEC with a value of 1 and its size to 9 bits. The output pin is then set to B4 of the micro. 3 4 A second Comms Tool (left) is linked to the output of the previous Comms Tool and also set to transmit, but the source is set to Text. You can then enter whatever 32 letter long message you want to display and set the output pin to B4. A Delay Tool of two seconds is then connected to its output (right). 5 6 A Digital Output Tool (left) is connected to the output of the previous Delay Tool, which brings pins C3 & C4 high, driving both wheels forward. This is connected to a 0.4s Delay Tool before going to another Digital Output Tool which brings these same pins C3 & C4 low again. After which it connects to a Sound Tool which outputs a small tune to the piezo buzzer, this Sound tool is then connected to the first two second Delay Tool to form an endless loop. SC siliconchip.com.au Australia’s electronics magazine January 2019  93