The Internet Power Line Adapter - University of Queensland
The Internet Power Line Adapter - University of Queensland
The Internet Power Line Adapter - University of Queensland
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Home Automation, <strong>Power</strong> <strong>Line</strong>s and the <strong>Internet</strong> Quenten Alick<br />
<strong>The</strong> chosen microprocessor must also have both an SPI (Serial Peripheral<br />
Interface) and an SCI (Serial Communications Interface). <strong>The</strong> SPI is needed to<br />
be able to communicate with the Intellon P300 network chip and the SCI<br />
interface is needed to communicate with the PC that will be running the web<br />
server. In order for the SCI interface to be able to communicate with the PC a<br />
RS232 transceiver must be used to convert the voltage levels from TTL to<br />
RS232 and vice versa. <strong>The</strong> MAXIM MAX232 RS232 interface should be able to<br />
perform this task with a minimum <strong>of</strong> extra circuitry.<br />
<strong>The</strong>re are a number <strong>of</strong> processors from the Motorolla range that are suitable. <strong>The</strong><br />
processors considered were from the MC68HC05 and the MC68HC11 range.<br />
<strong>The</strong> use <strong>of</strong> a MC60HC05C series would have been ideal since the Intellon<br />
development board already used one. <strong>The</strong> only drawback would have been the<br />
need to provide external ADCs since the MC68HC05C does not provide any<br />
internal ones. This would require more PCB space, making the board more<br />
expensive. However, the cost <strong>of</strong> purchasing another development kit for the<br />
microprocessor made this option non-feasible. Even if a development kit could<br />
have been found, the individual cost <strong>of</strong> $55 per microprocessor was also rather<br />
high. If this option had been taken, the cost would have risen about $310.<br />
This left the choice with the various MC68HC11 processors for which there<br />
were suitable development kits available. <strong>The</strong> microprocessor used in the<br />
development kits was the MC68HC11A1. This is an 8-bit processor with ADCs<br />
and a SPI and SCI interface and so meets the requirements. <strong>The</strong> 256 bytes <strong>of</strong><br />
RAM should be sufficient to store temporary variables, however the 512 bytes<br />
<strong>of</strong> EEPROM are insufficient to store data from the power meter.<br />
<strong>The</strong>re are several options available to address this problem. Firstly, the<br />
MC68HC11A1 development boards come with 8k <strong>of</strong> parallel SRAM, which is<br />
more than sufficient to store the required data. If necessary, the system could be<br />
demonstrated using the development boards. <strong>The</strong> preferred option would be to<br />
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