USING SINGLE-CHIP COMPUTER SYSTEMS FOR EFFICIENT AND COST EFFECTIVE ENVIRONMENTAL MONITORING

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1 Engineering e-transaction (ISSN ) Vol. 5, No. 2, December 2010, pp Online at Received 30 September, 2010; Accepted 21 October, 2010 USING SINGLE-CHIP COMPUTER SYSTEMS FOR EFFICIENT AND COST EFFECTIVE ENVIRONMENTAL MONITORING O. Ahmad 1, L. Gani 2 and N. Makbul 3 1,2 University Malaysia Sabah, Kota Kinabalu 3 Telekom Malaysia Sabah, Kota Kinabalu Malaysia othmana@gmail.com ABSTRACT Single chip computer systems started with the Basic Stamp computer system that solders computer parts into a printed circuit board, the size of a large Integrated Circuit (PICAXE). Now, true single-ics, as small as 8-pin in sizes, can become a complete computer system with all hardware and operating system. These are the PICAXE systems based on the Microlab PIC microcontrollers. A sample datalogger design, with its Basic source code is provided in the Proteus Professional software, and this circuit is simplified so as to use the least component and source code. It is used as the basis to test a simple application where temperatures are taken at a regular interval and stored in the non-volatile EEPROM memory. 181 bytes out of 256 of the EEPROM is used up by the Basic program loaded into the PICAXE-08M, the smallest PICAXE with 8 pins. The 40-pin PICAXE- 40X2 has 4096 bytes of EEPROM. As a computer system, users can communicate with the PICAXE IC using a serial port, and these serial ports can be linked to other devices, such as serial EEPROM or other computers, using the I2C protocols for large networks. The networks can be linked wirelessly but the simpler serial protocol, the RS232, will be the default for bootstrapping and communication. The cost of these computer systems is less than RM30 each so it could be cheaper and more effective to just produce lots of them and collect their data to be downloaded to a central server. This paper reviews PICAXE systems for their suitability to log temperatures of outdoor cabinets of Telekom Malaysia. Keywords: Data logger; Environment; Eeprom; Microcontroller; Single-chip computer system. 1. INTRODUCTION Data logging activity is vital in many research activities especially in studying the environments. It is therefore vital for researchers to get reliable and yet cost-effective systems that will allow them to collect accurate and reliable data. There are various ways of collecting data at remote sites: specialised data logging devices, personal computers to collect data, singleboard computers and lastly single-chip computers. Specialised data logging equipment is usually bulky, power hungry and expensive. Personal computers are even more expensive and power hungry but extremely flexible. Single-board computers are slightly better in power consumption and cost while retaining customisation flexibility. Single-chip computer system is the best in terms of power and price, while retaining the customisation and additionally increasing security of data. Single-chip computer systems are environment and water proofed because data is stored in eeprom forms instead of electromechanical devices such as hard disks. Wireless networks can solve some problems but wireless links are subject to weather and therefore not completely reliable. This research reviews the state of the art in single-chip computer systems especially in their uses in data logging activities. Single-chip computer systems mentioned in this article is different from the single-chip computers that are usually referred in publications (Dejun and Minjian, 2010). These single chip computers are normal microcontrollers that have lots of input-output devices and peripherals but are not stored with operating system support. It is also different from microcontrollers that are loaded with operating system firmware that are limited to larger microcontrollers 48

2 only and has not programming support. Single chip high level language interpreter can be traced back as far as the firmware developed by Myke Predko called BASIC87X, quoted from his book BASIC87x, was written to run on a PIC16F877(A) with the internal Flash program memory used for storage of both the interpreter (with user interface) as well as the execution code (Myke, 2008). PIC16F877 is a large microcontroller requiring 40 pins but now similar BASIC interpreter can be loaded into 8-pin microcontrollers as shown by the PIXAXE family and its clone KICCHIP. Work on data loggers is active as shown by Dynamic environmental management, United States Patent , Leslie (2005) had used PICAXE for a mobile robot, but literature search failed to find prior use of PICAXE for data logging activity, although there are mentions of single-chip computers. These are just alternative terms for microcontrollers such as PIC (Goswami et al., 2010; Kumar et al., 2010; Kirk et al., 2004). Järvinen (2007) wrote in the Journal of Education Technology that PICAXE could be used by Secondary School students to design electronic systems. PICAXE data logger cards were reported by Lorenz (2008) in a NASA progress report. These cards were off-the-shelf PCBs, which are equipped with PICAXE-18X and I2C EEPROM and sensors. 2. METHODOLOGY The research started with identifying with the problems. The area of research concentrates first on the monitoring of Telekom Malaysia s outdoor equipment cabinets. Their engineers and technicians are interviewed for their views on the methods and problems of collecting data. Various data logging technologies are reviewed. The internet search is best at the initial stage, especially Wikipedia. Data in Wikipedia may not be completely reliable or accurate but they are a good place to start identifying with available systems and suppliers. Detail analysis was carried out on the web sites of these equipment suppliers. Nowadays, all the major suppliers have websites. Those that do not have any website will be ignored. This methodology may not be computer systems with operating system support and complete but it is the most cost effective and fast, and suitable for the objective of the focus of the research, data logging of temperatures of outdoor cabinets. Once the environmental range has been identified, circuits were designed using Proteus Professional and source codes evaluated and run in Proteus VSM via Proteus ISIS schematic capture software. Proteus VSM is capable of simulating the compiled codes for PIC and other microcontrollers in HEX or COFF format and linking to its source codes either in assembly or high-level language provided the debugging information is included when the object code was produced. ISIS provides a graphical animation of the simulation process, as well as provide virtual serial, RS232 terminal. Proteus VSM is also capable of simulating PICAXE but only in Basic source code format. Sample circuits and Basic source code from Proteus were modified to suit a particular situation and the results are compared for various versions of PICAXE. A sample circuit diagram using PICAXE14M as a data logger is shown in Figure 1. The sizes of program codes are determined by the Syntax facility in PICAXE Development Environment, the PICAXE Programming Editor, developed by PICAXE (PICAXE, 2009). Some simulation was also done using the PICAXE Programming Editor. There are some discrepancies in the result shown by PICAXE Programming Editor versus Proteus VSM. This can only be settled once the real circuit had been built. For the moment, the Basic language execution simulation by PICAXE Programming Editor is given more weight than that provided by Proteus VSM. Some results shown by Proteus are also suspect since it cannot allow parallel inputs. This is a necessity because PICAXE uses one port dedicated for Bootstrapping while using other ports for communication. It means that results need to be shown at another serial port. This is not acceptable in real-life operation because it requires different terminal ports for bootstrapping and communication, creating more complexities cost and size. 49

3 Fig. 1 Circuit diagram of a PICAXE14M data logger 3. RESULTS AND DISCUSSIONS This is just an informal survey of the requirements for a localised (Telekom Malaysia) TM unit at Kota Kinabalu, their competence level and their equipment level in Item 10 of shows that some of their equipments still use RS232 interfaces. Their notebooks had to be provided with USB to RS232 converter. They need this to configure their switches and routings. Table 2 summarises data logging systems that had been studied. Table 3 summarises important specifications of the various PICAXE. Table 4 shows current prices for the PICAXE without postage and packing costs. There is no reason why the special purpose data logger cannot be implemented using PIC but it will always be at a disadvantage if it were purpose built. If it were implemented as a data logger that can be programmed like a computer and the size of a USB, then this data logger will join the entry number 4 of. Item 5 is the centralised monitoring system. TM has this system but the location of the sensor is not easy to customise. It is fixed during installation and the O&M team at Kuala Lumpur keeps its data. Table 1 Needs and situations for temperature logging for TM Cabinets. No Feature Requirement 1 Absolute Accuracy Low (1 C) 2 Linearity High 3 Data Quantity Low (10) 4 Accessibility High (At road sides, 24 hours/day) 5 Storage High (70 C) temperature of data logger 6 Storage space for Low (Around 1000 cc) data logger 7 Maximum temperature expected 8 Number of temperature sensors 9 Location for temperature sensor 10 Communication protocol 11 Available of PIC programmers 12 Assembly and C programming ability 13 Availablity of notebook 100 C (Maximum IC temp.) 5 Unknown, to be determined from time to time RS232 (existing equipment and practice) None None Yes 50

4 Table 2 Comparison of data logging systems No Type Cost Power Flexibility Security Sensors Comment 1 Specialised data logger High Medium Low Medium 1 Micro lite logger (8k samples) US$ 59 (RM195), Dealextreme SKU7003 US$ 8.80 (RM30) 2 PC based High High High Low High Weather station 3 One board Medium Medium High Low High Weather station PC based 4 One chip Low Low High High 5 PICAXE-14M (RM 10) computer 5 O & M High Low Medium Medium 1 Operation Room Table 3 PICAXE Summary and Sample Sizes PICAXE Inputs Lines of Code PIC PRO (byte) Data (byte) Samples (Test) Add memory 08M PIC12F None 14M PIC16F None 18M PIC16F None 20M PIC16F None 18X PIC16F C 28X PIC16F C 40X PIC16F C 20X PIC18F14K C 28X PIC18F C 40X PIC18F C Table 4 Prices from PICAXE Prices excluding Tax 08M M M M X 28X X X X X Figure 2 shows a printed circuit board, which is, can be bought from online suppliers to mount the PICAXE14M. Figure 3 shows the result of a simulated PICAXE14M programmed as a data logger. Figure 4 shows the utilisation of memory in PICAXE14M. 4. CONCLUSIONS For logging the temperatures of outdoor Fibre Optical Equipment, the PICAXE or its clone the KICCHIP will be recommended for TM purposes. As a computer, it needs skill in writing and modifying the Basic source Fig. 2 RKP14C with PICAXE-14M for (GBP 3.60 at Ebay) Table 5 Simulated terminal responses for an example of a PICAXE14M system Press address to read Address Temperature Upload comlete code but it is a much lesser learning curve than using Assembly or C compilers to do data logging as well as communicating with PCs and burning it to microcontrollers. 51

5 TM technicians and engineers have built-in experience and skill to be trained to modify the source codes. They are also well equipped with notebooks and serial RS232 connectors and ways of communicating with their equipment. It is this communication aspect, which makes it difficult to write and modify custom microcontroller codes. PICAXE has the routines already embedded and can be called via Basic source code commands. and technical monitoring. Availability of skilled engineers and technicians will not hamper their requirements for more programming expertise, although even the most advanced PICAXE system, the PICAXE-40X2 with its 256 bytes of data storage capacity, will not be sufficient for all data logging uses. If necessary, more memory can be added by using the I2C protocol but this will add to the size and cost of the whole system. REFERENCES Dejun, L. and Minjian, W., Design and Implementation of Data Acquisition System Based on Single-Chip Computer, Second International Conference on Computer Engineering and Applications Goswami, A., Bezborouah, T. and Sarma, K., An embedded design for monitoring and controlling temperature Indian J. Physics 84(1): 71-9 Järvinen, E.M., Karsikas, A. and Hintikka, J., Children as Innovators in Action A Study of Microcontrollers in Finnish Comprehensive Schools Journal of Technology Education 18(2): Fig. 3 Memory status shown by PICAXE Programming Editor for a PIXAXE14M For TM requirement, the cheapest PICAXE the PICAXE-08M is sufficient. With its capacity to store up to 72 samples, it should be possible to get halfhourly sample for 24 hours. However, the price difference between PICAXE-08M and PICAXE-14M is so small that the extra ports available will be useful for further customisations by adding extra features or sensors. USB data loggers may be getting smaller in size and prices but it is still too expensive. It may have advantages in ease of use and large sample sizes but its lack of customisation will be a major obstacle for many other data logging uses. Commercially produced single-chip computer system, like PICAXE, based USB data loggers are still not available. Even if it were to appear, it will not be cheap initially but that era is most welcomed. At present, custom-built PICAXE systems is still the most recommended data logging system for research 52 Kirk, M., Jane, K.H. and Royan, O., Environmental Sensor Networks, IEEE COMPUTER 1-6 Kumar, A., Singh, I.P. and Sud, S.K., Design and Development of Multi-Channel Data Logger for Built Environment, Proceedings of the International MultiConference of Engineers and Computer Scientiest Leslie, A., Mobile Robot Guidance and Navigation, Thesis for the Degree of Bachelor of Engineering (Control and Instrumentation), University of Southern Queensland Lorenz, R.D., A 20-station array of intelligent dataloggers to study terrestrial dust devils: preliminary trials,, Lunar and Planetary Science, Year 1 Progress Report NASA Award Number, NNX07AL32G Myke, P., Programming and Customizing the PIC Microcontroller, Third Edition, McGraw-Hill PICAXE, Revolution Education Ltd., PICAXE Manual Version /2009