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PICAXE Part 1: Assembling your Schools Experimenter board In the first part of this new series, we look at how to build and test a very low cost experimenter’s kit based on the PICAXE-08M microcontroller chip. Next month, we will introduce some more formal programming exercises for schools to use in the classroom. D ubbed the “Schools Experimenter”, this versatile design allows simple exercises to learn the BASIC programming language using LEDs and simple sensors, but the board can also be used alongside a breadboard prototyping system for much more advanced experiments. What is a microcontroller? Microcontrollers are single-chip computers that are finding use in just about every electronically enabled device you care to name. Toys, mobile phones, microwave ovens and MP3 players are just a small sample of the consumer items now microcontroller equipped. The “PICAXE” system is a power- # About the Author: Clive Seager is the Technical Director of Revolution Education Ltd, the developers of the PICAXE system. 86  Silicon Chip by Clive Seager # ful, yet very low cost microcontroller programming system designed to simplify educational and hobbyist use of these devices. A unique feature of the PICAXE system is that no special programming hardware is required. Programs that you write on your PC using free Windows software can be downloaded straight into the microcontroller chip with a direct cable connection. This low-cost approach also means Table 1: PICAXE-08M Pinouts and Functions Pin 1 2 3 4 5 6 7 8 Function Description +V Power supply positive (4.5V to 5V only) SERIN Serial input for programming IN 4/OUT 4 General-purpose input/output 4 IN 3 Digital input 3 IN 2/OUT 2 General-purpose input/output 2 IN 1/OUT 1 General-purpose input/output 1 OUT 0 Output 0 (also used as serial output) 0V Power supply ground (0V) Use LDR input Switch input Green LED Yellow LED Red LED - siliconchip.com.au that students can use the whole programming system at home. Naturally, the easiest-to-use member of the PICAXE family, the PICAXE-08M, was chosen for use in this project. It is contained in an 8-pin dual-in-line (DIL) IC package. Two pins connect to the power source, two more are used for downloading the BASIC programs while the remaining four are general-purpose inputs and outputs. These can be used to control LEDs and relays, make sounds, read sensors, etc. Some pins have alternate functions, which we’ll explore in more detail in future articles. Schools Experimenter In short, the Schools Experimenter board provides a socket for the PICAXE-08M microcontroller as well as a series of simple devices (LEDs, switches, etc) that you can control and interrogate with your BASIC programs. A socket is also included for programming purposes. More detail is to be had from the complete circuit diagram in Fig.1. Red, yellow and green LEDs are connected to the first three outputs (outputs 0, 1 and 2) of the PICAXE. A 330W resistor in series with each output limits LED current flow to less than 10mA. A piezo transducer can also be connected to output 2 for making sounds and playing musical tunes. Not surprisingly, a miniature push-button switch (SW1) on input 3 and a light dependent resistor (LDR) on input 4 act as the on-board input devices. Each input has a 10kW pulldown resistor (to the 0V rail) to ensure correct operation; this will be explained in more detail next month. A serial download socket and 10kW and 22kW resistors make up the computer interface for programming. The PC board also contains provision for a 10-pin header strip (H1) that enables each of the input/output pins to be connected to a breadboard for more advanced experiments. The three holes marked “H2” are reserved for future use and can be ignored at present. Finally, a 100nF capacitor is included for siliconchip.com.au CALLING ALL SCHOOLS with electronics/technology courses: Want some FREE PICAXE PC boards? Here’s an offer you don’t see every day: FREE PICAXE blank project PC boards. Yes, free. Or gratis, zip, zilch, without charge, nothing... just as long as you qualify AND you’re quick! To celebrate the launch of our “PICAXE in Schools” column, Revolution Education Ltd has kindly donated 2000 “Schools Experimenter” PC boards, as used in this feature, to be given away, free of charge, to Australian and New Zealand High Schools. The first 200 teachers to email (NOT phone!) their full name, school, position and school address to siliconchipoffer<at>microzed.com.au will each receive not 1, not 2 but a whole 10 PC boards – absolutely free of charge! Your email will be acknowledged within 24 hours but please allow up to 30 days for delivery. * The fine print: limit 10 boards per school. Blank PC boards and programming sockets only supplied (ie, no components), as shown above. Strictly while stocks last, and in order of receipt. For special deals on kits of parts, visit www.microzed.com.au high-frequency power supply decoupling. Table 1 shows the function of each physical pin on the PICAXE08M chip and how it is used on the Experimenter’s board. Note that the 4-pole dual-in-line (DIL) switch on the PC board can be used to disconnect the LEDs, switch and LDR from the PICAXE input/outputs. This allows the input/outputs to be used for other purposes when experimenting with a breadboard. For the time being, all four contacts of the switch must be closed (set to the “ON” position). Putting it all together Assembly of the Schools ExperiMay 2005  87 Fig.1: the complete circuit diagram shows how simple it is – there are only about a dozen components! menter is quite straight-forward. Begin by soldering all of the resistors in place using the overlay diagram in Fig.2 as a guide. We’ve shown all the resistor colour codes (all three of them) in a table elsewhere in this feature. Alternatively (or as well as?), a quick check with your multimeter will also confirm resistance values. Next, install the IC socket for the microcontroller (IC1) followed by the two switches (SW1 & SW2). The 4-pole DIL switch (SW2) must go in the correct way around (see photos). The serial programming socket can be installed next; make sure that it is pushed right down on the surface of the PC board before soldering. Follow with the three LEDs, The completed schools Experimenter, ready for the addition of a 4.5V battery pack (ie, 3 x AA cells, NOT 4!) 88  Silicon Chip siliconchip.com.au Fig.2: Here’s how to place the components on the PC board. Use a socket for IC1. LDR and 10-pin header (H1). Note that with the flat (cathode) sides of the LEDs must be oriented as shown, while the LDR can sit about 5mm proud of the board surface. The last job is to solder the wires for the battery clip and piezo to their respective pairs of pads. Pass the wires through the adjacent strain-relief holes before soldering (see photos). Make sure that the positive (red) wires connect to the pads marked “+”! When inserting the PICAXE-08M into its socket, it is very important that the indented (pin 1) end is oriented as shown on the overlay diagram and photos. Your completed project should be powered from a 3 x AA alkaline cell (4.5V) battery pack or a regulated 5V DC supply. Never use a 9V PP3 battery, as this is way above the voltage rating of the chip. Take particular care that you have the power leads around the right way; otherwise, you’ll destroy the PICAXE chip! Programming introduction The easiest way to check that your board is working properly is to type in a short BASIC program and download it to the PICAXE micro, so let’s do that next. Those new to PICAXE programming will first need to download the Programming Editor software from www.picaxe.co.uk and obtain a low-cost download cable from their local distributor (see parts list). Connect the download cable to the serial port at the back of your siliconchip.com.au Yeah, we know, this photo is turned 90° compared to the overlay at left. But between the two, you should be able to identify and place all components. Parts List – PICAXE Schools Experimenter 1 1 1 1 1 1 1 1 1 1 AXE092 PC board 3.5mm stereo socket miniature pushbutton switch (SW1) 4-pole DIL switch (SW2) 8-pin IC socket miniature piezo transducer 10-pin SIL 2.54mm (0.1”) pitch header (H1) 100nF polyester capacitor (code 100n or 0.1mF) battery clip 3 x AA battery holder Semiconductors 1 PICAXE-08M 1 5mm green LED 1 5mm red LED 1 5mm yellow LED Resistors (0.25W 5%) 3 10kW 3 330W 1 miniature LDR 1 22kW Also required (not in kit) PICAXE Programming Editor software (v4.1.0 or later) PICAXE download cable (part no. AXE026) 3 x AA alkaline cells Obtaining kits and software The design copyright for this project is owned by Revolution Education Ltd. Complete kits (part no. AXE092K) or the PC board only (part no. AXE092) for this project are available from authorised PICAXE distributors – see www.microzed.com.au and resellers. Phone MicroZed on (02) 6772 2777. The PICAXE Programming Editor software can be downloaded free of charge from www.picaxe.co.uk or ordered on CD (part no. BAS805). May 2005  89 Sample Program main: high 0 pause 500 low 0 high 1 pause 500 low 1 high 2 pause 500 low 2 goto main ‘red LED on ‘wait 0.5 second (=500ms) ‘red LED off ‘yellow LED on ‘wait 0.5 second (=500ms) ‘yellow LED off ‘green LED on ‘wait 0.5 second (=500ms) ‘green LED off ‘jump back to start Fig. 3: a screen grab of the chip and port setup from the programming editor software. Make sure you set the details correctly or it won’t work! In the background is the sample program, again reproduced in Fig. 4 (above right). computer. Note that if you have a late-model laptop without a serial port then you will also need to purchase the USB to Serial Adapter (part no. USB010). After installing and running the Programming Editor software, select View -> Options from the toolbar and configure the software for “PICAXE-08M” mode (see Fig.3) Also, make sure the serial port number (COM1, COM2, etc.) corresponds to the physical port where the cable is connected and then click OK. Now type in the test program shown in Fig.4. Be sure to include all punctuation, including the colon (:) after the first word “main”; this tells the computer that you want the word “main” to be a label. This enables the program to later use the command “goto main”, i.e. jump back to the start. When the program is complete, click PICAXE -> Run to download the program into the PICAXE chip. Note that programming can only be successful if the cable is connected and power is applied to the PC board. All being well, the three LEDs will light in turn. Don’t be worried that the red LED on output 0 flickers during a download; this is normal, as the LED is indicating that the computer and PICAXE chip are communicating. Troubleshooting If the program fails to download, disconnect power and recheck all of your soldering and component placement and orientation. If no problems can be found, use your multimeter to verify that there is 4V The PICAXE has a maximum 5V supply and operates quite - 5V between the happily at 4.5V. For this you need either a special threepower pins (1 & cell “AA” battery holder, as shown here, or a four-cell 8) of the PICAXE modified to take three cells, to ensure that the 5V limit chip when power isn’t exceeded. is connected. Finally, check that the download look at how to write programs that cable is fully inserted in its socket respond to inputs (both digital and and that the serial (COM) port analogue) and how to make sounds chosen under the View -> Options on the piezo transducer. In the meantime, if you’re an menu matches the port that the electronics or technology student cable is physically plugged into. in an Australian or NZ school, make Summary sure you show this article to your Congratulations – you have teacher so your school can claim now assembled and programmed their 10 PC boards. Remember that it is strictly first your first PICAXE microcontroller SC project! Next time around, we’ll come, first served! Resistor Colour Codes o o o Qty. 1 3 3 90  Silicon Chip Value 22kW 10kW 330W 4-Band Code (5%) red red orange gold brown black orange gold orange orange brown gold 5-Band Code (1%) red red black red brown brown black black red brown orange orange black black brown siliconchip.com.au