Saturday, June 6, 2009

Getting the tools part 2: a matter of levels

After choosing the main component of the project in a previous post, we also have to connect it :-)
On one side we have the CANbus connector, on the other (probably) a PC used to understand what informations are going up and down on the CAN. Unfortunately we can't connect PC directly to CANbus, due the lacking of a suitable peripheral on PC. So we choosed a PIC18F4682 to do the raw job. So is it all done?


Connecting directly CAN, PIC and PC probably will result in a big roast, with nothing to eat :( . So we will use these two tiny chips, ready on the breadboard:
Their work is to convert voltage levels in a suitable way.

MAX232CPE from Maxim is a level converter for RS232 (serial) protocol. It converts +12/-12 signals from PC serial port to +5v accepted from PIC, and do the opposite job on the other direction. To do this it needs some condensers, not yet installed, to produce the necessary voltages, cause it's main voltage is only +5V.

MCP2551 from Microchip converts CANbus signals (what is the voltage on Vectra CAN bus? we still don't know...) to PIC level. We HOPE that this interface chip will do the job, cause the real implementation of CANbus on Vectra (voltage, speed, protocols, messages...) is still totally unknown. MCP main voltage is also +5V.

On the left side of the first photo you can see a bunch of components and wires. This will be our 5V power plant. LM7805 with 2 condensers will give power to all our chips and components we will use in this project. Now it is time to connect everything: stay tuned!

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